TT_Diversity_of_Life Flashcards
(826 cards)
1
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Birds 1
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3
Q
When did all the key charcateristics of birds evolve?
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Before modern birds evolved themselves.
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Q
Birds have less variability than any other vertebrate classs, but…
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… have wider ranges and more diversity than any other class.
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Q
How many spcies of birds are recognised currently?
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11000
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Bird characteristics, none of which are unique to birds:
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Endothermy, feathers, powered flight, hard-shelled eggs laid into a nest, light bones and keratinaceous beaks with no teeth.
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Q
Birds have light bones.
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They are pneumatised– air-filled.
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Q
Birds are endotherms.
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Typical range: 40-42°C. High metabolic rates.
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What % of bird species are capable of powered flight?
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98%. Flight is a basal character of modern birds.
10
Q
When was the first specimen of Archaeopteryx discovered?
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1861, there were 11 subsequent specimens, but they were variable– are they even the same species?
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Archaeopteryx as a transitional form:
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Feathers on the wings, but heavier, with toothed jaws, unlike modern birds.
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Q
When do the Archaeopteryx fossils date back to?
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Jurassic, ~150 mya.
13
Q
In what % of cases do birds exhibit biparental care?
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> 90%.
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Archaeopteryx is the archetypal first bird, but no fully-formed bird emerged at a single point in time. Characteristics appeared more gradually.
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Hinge-like ankles, bipedal posture and simple, filamentous feathers emerged in the Dinosauria. The furcula emerged in the Therapoda. Vaned feathers emerged in the maniraptora. Wings emerged in the Paraves. The pygostyle (fused tail) emerged in the Pygostylia. The keeled sternum emerged in the Ornithoraces. The last two traist evolved after the origin of Aviales.
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Q
What features define a bird?
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This depends on when you think birds emerged, and vice versa.
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The dinosaurian origin of birds is useful for determing why bird features evolved.
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- Feathers vs. flight. 2. Evolutionary origins of parental care. 3. Genome structure.
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Feathers vs. Flight:
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Feathers pre-date the evolution of flight, so cannot have initially evolved to aid flight.
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Evolutionary Origins of Parental Care:
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Recent fossil evidence suggests that theropods brooded tehir eggs like modern birds, unlike any other reptile, which suggests the importance of parental care in birds may be an ancestral character.
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Explosion of fossil information in the early 1990s:
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Exceptional preservation from 130-120 mya (Cretaceous). E.g., Jehol biota from northeastern China.
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Q
When did birds first diversify?
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There have been multiple radiations of birds, beginning in the Creatceous.
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Entantiorthonines were a major Creatceous radiation.
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More than 90 genera. >50% of Cretaceous birds. None survived past the end of the Creatceous.
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Entantiorthonines Characters
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Largely arboreal, heavier skull morphology with toothed jaws, the toothed jaw evolved into a beak by the end of the Cretaceous (convergent with modern birds) and a unique feather structure.
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Unique Feather Structure in Enantiorthonines:
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Long, flat;extended feathers, unlike anything found in modern birds.
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Q
How was growth in Enantiorthonines different to modern birds?
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All modern birds grow in the first 1-2% of their lives, but this group had slow grotwh, overlapping with reproduction– unlike crown-group birds. Inferred from bone structure.
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Why did birds have a poor fossil record until recently?
Pneumatised bone, small and light.
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Modern Birds
Neornithes.
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When were Neornithes thought to originate ten years ago?
Most birds originated during the Creatceous based on DNA evidence.
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When is it now thought that most birds originated?
Immediately following the K-T mass extinction event in an explosive radiation (the Big Bang model). However, the origins of some groups did occur before the K-T extinction event.
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What Neornithe groups originated prior to the K-T extinction event?
Waterfowl, ostriches and Galliformes (chickens).
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What changed to transform our understanding of when most modern birds evolved?
More early fossils of ancestors of current birds, and an explosion of data from genomes, providing improved resolution.
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The Most Diverse Clade of Birds
Passeridae (finches, warblers; crows etc.) diversified most recently.
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Raptorial Life-History
I.e., obligate predatory behaviour evolved multiple times independently.
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There are multiple origins of the aquatic lifestyle.
E.g, pelicans, flamingoes, ducks and waders.
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There is a subset of birds that learn their song, and sing different songs under different conditions.
Multiple origins of vocal learning in birds, e.g., songbirds, parrots and hummingbirds.
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There are two older clades of modern birds.
Paleognathae (~95 mya) and Galloanseres (~80 mya).
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Paleognathae
The oldest group of modern birds. Few species, flightless or poorly-flying. Tinamous and Ratites. Primitive birds with semi-differentiated sex chromosomes.
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Ratites
Ostrich, cassowary, emu and kiwi.
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Tinamous
47 species found in Mexico, Central and South America. Crytipc and difficult to spot. Derived lineage within the Paleognathae. Can fly!
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Many Paleoganthae species were extant until human colonisation.
E.g., Aepyornis/elepahnt bird and Moas in New Zealand.
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How was Paloegnathae originally thought to have diversified?
All extant Paleognathae are found in the Southern hemipshere, so this and the assumption of monophyly has been used as evidence that they diversified when Gondwana broke up-- an example of vicariance leading to speciation.
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Current Hypothesis for Plaoegnathae Diversification
Early ratites flew the lost flight at least 3 times as a response to the freeing of niches vacated by dinosaurs. Ratites represent a case of convergent evolution.
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Evidence for the current hypothesis for Paleognathae diversification:
Tinamous can fly, so the ratites are not monophyletic. Strict parsimony doesn't apply as flight has been lost multiple times, but never gained as far as we know. The mtDNA-based phylogeny differs form the phylogeny expected under the vicariant model, e.g., elephant birds are the most recent ancestor to the kiwis despite differences in their geographical distribution. Dating suggests divergence within the ratites occurred mostly after the K-T boundary.
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Large Body size in Ratites
Evolved multiple times independently.
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Birds exhibit restricted body form in comparison to other vertebrate groups, e.g., minimal vraiation in body weight.
5 log units between the smallest and largest birds in weight (beee hummingbirds and ostriches).
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Not much more variation in fossil and sub-fossil birds.
Dromornis stirtoni, Dinornis and Phorusrhacoids were similar in body weight.
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There is much more variation in body weight within other vertebrate groups.
Mammals: 8 log units. Reptiles: 7 log units. Fishes: 10 log units. Amphibians: 6.5 log units.
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Birds are invariant in terms of reproductive biology.
All birds are obligately oviparous/all birds lay eggs. Mammals can be placental, nonplacental, or lay eggs. Reptiles and fishes are both oviparous and placental.
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Flight was thought to be a constraint on avian form.
Hence, light bones, and low mass. High basal metabolic rate may place alower limit on body size due to excessive heat loss with a large surface area:volume ratio. Obligate egg-laying as a consequence of flight?
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Why should features of modern birds not be used as reasons why modern birds are invariant?
Most of these tarist evolved in dinosaurs, and there are only a few evolutionary transitions to work with.
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Birds have huge ranges.
Their altitudinal and geographical ranges are the largest of any animal.
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Birds' Altitudinal Range
Ruppell's vulture: 11.3 km. King penguins can dive uo to 0.5 km deep!
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Birds' Geographical Ranges
Kittiwakes have a large geographical range due to migration. The south polar skua is found at 90° S.
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Birds' Altitudinal Range (Breeding)
Alpine chough: 5.8 km. House sparrow: -0.6 km deep as they can breed in coal mines.
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When was the first full genome sequence of a bird?
2004
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Chromosomes in Birds
Females are heterogamous: ZW. Males are ZZ. Birds have micro- and macro-chromosomes.
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Bird Genomes
Conserved organisation. High rates of recombination (2-20-fold higher than in mammals). Similar number of genomes to mammals (20-23,000). Overall size is small: 1.05 billion base pairs compared to 2.5 in mice and 3.1 in humans. Fewer repetitive elements (10% of teh genome comapred to 40-50% in mammals).
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Why do birds have small, compact genomes?
Small genome size enables a small cell size. Large Sa:V ratio of cells enables elevated metabolic rates.
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Small genome size was thought to be an adaptation for flight.
Flight is very metabolically demanding, and bats have smaller genomes than other mammals.
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Organ et al., (2007)
Studied cell nuclei in osteocytes in animals and dinosaurs, and found that small genome size pre-dates the evolution of flight as small genomes were found in dinosaurs before modern birds evolved. It is now thought that small genome size didn’t enable flight to evolve, but evolved as a consequence of flight.
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Birds 2.
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Key adaptations enabling avian diversity.
Adaptive flexibility through the use of keratin (feathers and beaks). Long distance movement through flight.
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Contour Feathers
Have a plumaceous section at the bottom for insulation, and a pennaceous section at the top for the mechanical structure as well as carrying pigments and structural colouration.
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How many different types of feather?
7
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What allows great flexibility as well as flexibility in feathers?
Movemnet of distal hooklets (barbicels) in proximal barbules.Barbules have barbicels on one side and grooves on the other. The hooklet/barbicels and grooves interlock, which creates a planar, laminar surface.
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Modification of Feather Microstructure
typically modifies characters associated with thermal properties, waterproofing and aerodynamics.
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Modification of Feather Macrostructure
Typically modifies sructural or directly functional properties of feathers, e.g., the thickness of the central rachis is often modified.
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Number of feathers are also subject to modification.
The number of primary feathers is usually invariant (9-11 in the outer wing), the number of secondary feathers varies hugely. E.g., the Rufous hummingbird has 6, but the Laysan albatross has 40.
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Sandgrouse
15 species that breed in the desert.
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Young sandgrouse have higher demands than adults. How do they get water to the offspring?
The male soaks its belly feathers in watering holes, which have high retention due to the coiled structure of the barbules.
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Success of Water Transport by Sandgrouse
Allows for water transport up to 30 km with ~60% successfully transferred to the offspring.
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How does the helical structure of the barbules confer high water retention?
The helical barbule structure uncoils when wet, forcing feather expansion as the uncoiled barbules force the barbs apart, and hence, water retention.
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Silent Flight in Owls
The serrated leading edge, and long, filamentous barbs on the trailing edge break up larger air vorticles over the wing into many smaller ones. This reduces the air turbulence and the sound produced.
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Large-scale feather structure modification in woodpeckers:
They sue a highly thickened rachis as a support for balance, when pecking at trees.
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Anti-icing properties of penguin feathers:
Penguins have very fine barbules on the end of feathers.
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Feathers as items for sexual display:
The marvellous sptauletail (a hummingbird) has a modified tail feather on each side with barbs and barbules only at the end. The standard-winged nightjar have a much longer and thicker central rachis on secondary feathers.
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Consequences of Feathers for Avian Evolution
1. Annual cycle governed by the need to replace feathers during moults. 2. Diversity of shapes, forms, colours and structures that feathers allow may have have facilitated high rates of speciation. 3. Enabled worldwide dispersal, and migration to exploit seasonal and ephemeral and seasonal habitats.
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Why is moulting of feathers required?
Feathers are inert structures that are non-living once they stop growing. They wear.
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Moulting is related to the flight behaviour of individual species.
E.g., waterfowl lose all their feathers quickly, so are temporarily flightless, but can escape feathers on the water. Whereas, birds that fly long distances often moult almost constantly somewhat. Most birds moult in the summer after they've bred as it's hot enoygh that they don't need to thermoregulate well, and food is typically abundant.
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How many different cone cells do birds have?
4
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Biochrome Pigments
Melanins (black, brown and rufous), carotenoids (orange, yellow) and porphyrins (purple, green).
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From where are biochrome pigments obtained?
Melanins and porphyrins are synthesised by the birds themselves, whereas carotenoids must be obtained from the diet, e.g., from fruit.
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Structural Colours
E.g., blue. Work by alteration of incident light, e.g., by coherent scattering from nanoscale particles such as melanin granules.
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Diversity of feather structure was higher in the past than it is now.
There are at least 4 feather morphologies found in theropods, but not in modern birds. All current types of feather are also found in theropods.
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When did feathers originate?
The earky origin of feathers: ~250 mya. The late origin of feathers: ~165 mya.
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What may push back the origin of feathers even further?
Some pterosaurs have been found to have feathers.
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Developmental Pathways Controlling Feather Development
Homologous to those that control scale, denticle and hair development from epidermal placodes. These pathways involve expression of Fibroblast Growth Factor (FGF) and Sonic the Hedgehog (Shh).
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Default State in Birds
Feathers.
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Beak Structure
A guide to feeding specialisation, and is key to how access to resources is partitioned in an ecosystem-- ecological differentiation.
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Probers
Beak morphology ranges from deep to shallow.
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Surface Feeders
Beak size ranges from small to large.
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Other type sof beak morphology related to feeding:
Pickers and sweepers.
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How are adaptive radiations often most obvious?
In terms of divergence in beak morphology, e.g., honeycreepers in Hawaii (~5 mya). Darwin's finches are similar other than in beak size.
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How did Lack hypothesise that the adaptive radiation of finches could be explained?
By species evolving to exploit vacant niches-- the nicjes suggested by the variation in beak size and shape.
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What has changed in fimches?
Underlying the changes in the keratin structure in beaks, skull morphology has also changed.
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What have recent phylogenomic analyses revealed regarding radiations of finches?
Diversity in finches is young (~1 mya), and multiple lineages provide evidence of extensive introgression (gene exchange) via hybridisation.
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What controls beak length?
Calmodulin. Over-expression of Calmodulin in chicken embryos leads to elongated bill length.
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What controls beak depth?
MP4.
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How many birds take part in annual movements?
~25% of all individual birds. 5 x 10^10 individuals.
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What implies migration is due to seasonal changes (predominantly)?
Migration is mostly north-south not east-west.
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Geolocators
Enable more accessible tracking of birds than ringing. Clock and light sensor enables estimation of position by +/- 100km.
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Ringing of Seabirds
Biased as it depends on where the sea birds wash up.
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Swifts
Spend the first 3 years of their lives in the air, before they breed. Swifts migrate from Europe through West Africa to Central Africa.
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What did geolocator tracking of Manx shearwaters reveal?
Their looping migration between Europe and South America with stop-off points in the Atlantic. No sleep. Metabolic rate 8-10x greater than normal continuously. Speed from 1,067-1480 km per day. Non-stop tracking distance ranged from 7,008 to 11,680 km with flights from 5.0 to 9.4 days.
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Bar-Tailed Godwits
Migrate from Alaska to New Zealnd, so positioning during flight has to be very accurate. Satellite tags on these birds gave direct measurements of tehir flight speed and capacity.
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What birds carry out the largest migration of all birds?
Arctic terns migrate from the Arctic to the Antarctic to exploit solar energy fluxes, though they do stop to feed along the way. They track the region with the highest solar energy.
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What can be used to predict the movement of migratory birds?
Vegetation growth.
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What do migratory patterns often reflect?
The evolutionary history and the effect of past climate on a species.
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Leapfrog Migrations
A widely-distributed species where the northern populations winter furthest south, e.g., foxtails or swallows. Swallows northern Sweden winter furthest south in Africa.
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Migratory Divide
The population shows a split in its migratory direction, e.g., the willow warblers where two different subspecies meet in a hybrid zone in northern Sweden. They were split into refugia during the last glaciation, thus their different migratory routes reflect range expansion.
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Non-Adaptive Migratory Routes
Species migrating unnecessarily far such as Wheatears that colonised North America, but still migrate 11,000-18,000 km to Africa.
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Blackcap Bird
Breeds in the UK (and the rest of Europe) in summer when they are insectivorous, and migrates to north africa in the winter when they are herbivorous (mostly frugivores).
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Migratory Timing and Direction
Strongly inherited.
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In the 1950s, blackcaps began to winter in the UK.
Ringing experiments suggested these had migrated from central Europe.
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Patterns of Blackcap Migration from Europe
Birds breeding in north and west Europe migrate south west. In Austria, there is a migratory divide at 14 °E, east of which point, birds migrate to the south east. A small proportion of central European birds migrate northwest (e.g., to the UK).
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Plant-Plant Interactions
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Positive Effects of Plants on Each Other
Accumulation of nutrients, provision of shade, or protection from herbivore. However, they may compete for resources. The relative importance of competition and facilitation vary.
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Mechano-Stimuli
Can acts as cues for neighbour presence.
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Volatile Organic Co,pounds
Secreted by fruits, flowers and leaves, and used in defence responses.
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Root Exudates
Secrete a variety of organic compounds into the rhizosphere that may indicate kinship.
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Root Choice Test
A maize seedling in a Y-shaped inverted tube. The primary root of the seedling grew significantly more towards the growth solution of the plant that had not previously been stressed.
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Plant Repsonses to Neighbours
Can be modified by above-ground stresses, and are mediated by below-ground interactions.
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Types of Plant-Plant Interactions
Competitive, commensal or asymmetric.
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Competition
Neither partner gains, e.g., between crops and weeds.
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Commensal
Facilitation at the interspecific level, e.g., epiphytes. Cooperation resulting in adirect benefit to one partner at the intraspecific level.
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Asymmetric
At the interspecific level, it can be alleopathy, or parasitism. At the intraspecific level, it's altruism: preferential help is given to other individuals in the same populations.
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Facilitation
The 'helper plant' provides benefit to another plant, but does not incur any cost.
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Cooperation
E.g., swamping predators by masting: producing tonnes of seeds simulatneously at not cost to the producer, but seeds may be eaten, so would benefit others.
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Allelopathy
One partner benefits at the cost of the other. Release of inhibitory allelochemicals via the roots to affect the growth of neighbouring plants of other species.
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Parasitisim
Plants that derive nutrients at cost to their host.
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Altruism
A plant community supports a more elongated, taller plant in a dense stand, which both receives more light and shades its neighbours.
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What % of angiosperms are parasitic?
1.2%, i.e., 4750/ 369,000. Evolved 12 times across the angiosperms. Morphologically diverse: from parasitic trees to endoparasites.
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Obligate Parasites
Require a host to complete their lifecycles.
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Facultative Parasites
Can complete their lifecycles without a host, but will do better with one.
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Holoparasites
Take all of tehir food at cost to their host. Derived parasites. They don't even produce leaves.
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Hemiparasites
Derive nutrients from tehir hosts, but still make some of their food themselves. E.g., misteltoe has no roots, but still has leaves.
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Hemiparasites will not grow on all the plants in a complex community, e.g., a meadow.
Grasses are susceptible to the parasites as they have no defences to stop it attaching to their roots, whereas forbs (e.g., clover, broad-leafed plants) carry out lignification to seal off the parasite and eject it.
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Hemiparasites can be ecosystem engineers that suppress the dominance of grasses.
This has an indirect effect on neighbouring plants as there will be more nutrients for the surrounding plants. When the parasitised grass dies, more nutrients are available for wildflowers, forbs etc..
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Parasitic plants can also be problematic weeds.
Witchweed (Striga) kills over $10 billion worth of cereals and legumes each year. Broomrapes (Orobanche and Phelipanche) are problematic weeds of various crop species in southern and eastern Europe, the Middle East and north Africa.
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Cistanche
The stem is deep below ground. Trees are planted in long lines, shelter forests, to prevent tehd esert spreading by dust storms. Cistanche can be grown on these trees as parasites,w hich require minimal irrigation and could be a future food source.
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Plastid Genomes of Parasitic Plants
Highly reduced as well as highly conserved in structure and gene content.
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The first palstid genome of a parasitic plant was sequenced in 1992.
This plant, Epifagus virginiana, lacks all the genes for photosynthesis and chlororespiration found in the chloroplast genomes of typical green plants. The 70,028-base-pair genome contains only 42 genes, at least 38 of which specificy components of the specify components of the gene expression apparatus in plastids.
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Cytinus hypocistis
Has an extremely divergent genome that is among the smallest sequenced to date (194 kb). Only 23 genes.
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Why are chloroplast genomes filled with junk DNA?
They are no longer photosynthesising, and have undergone relaxed evolution.
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Possible loss of the chloroplast genome in the parasitic plant, Rafflesia:
None of the indentified plastid genomes had intact open reading frames. Phylogenetic analyses suggest ~33% of these remnant plastid genes may have been horizontally transferred from the host plant genus.
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Haustorium
A specialised, multicellular organ in parsitic plants that forms a physiological bridge to the host from which it will draw down nutrients. Hormones, viruses, proteins and mRNA transcripts can also be transported via the haustorium. Xylems, and sometimes also phloems, connect in the haustorium.
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Endoparasitic
Endophytic holoprasite. Plants that live within plants.
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Why were Rafflesia's evolutionary origins difficult to discern?
It's difficult to preserve.
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Rafflesia is an endoparasite.
It only emerges by breaking out from its host to flower and seed. It goes straight from its embryonic phase to its flowering phase. It spends most of its lifecycle as a string of cells instead of in a vegetative state.
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Selective Advantage of the Endoparasitic Mode for Plants
May be to avoid herbivores, and live in a constant environment.
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Endoparasitism evolved independently in at least 4 lineages.
Rafflesiaceae, Mitrastemonaceae, Apodanthaceae and Cytinaceae.
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What demonstrated that endoparasities evolved by convergent evolution?
mtDNA places Rafflesiaceae and Mitrastemonaceae in different orders: Malpighiales and Ericales respectively.
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Key difference between hemi- and holoparasites:
Hemiparasites still have chlorophyll, whereras holoparasites don't.
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Distribution of Parasitism
Broad distribution throughout the angiosperm phylogeny.
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There is one parasitic gymnosperm.
Parasitaxus usta. It grafts onto its host, and is found in the New Caledonian islands.
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Hydnora
Fly- and beetle-pollinated parasitic, basal angiosperm.
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Prosopanche
Basal angiosperm parasite that has a Rhizome with cable-like roots to attach to the host.
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The Family Orobancheaceae
Hemi- and holprasites both belong to one family. Used as a model for studying parasitic plant and plastome evolution. Parasitism evolved just once in this family. Chlorophyll was lost 5 times in this family.
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Disintegration of the Family Scrophulariaceae
Previosuly one of the largest families, but DNA sequencing indicated it was polyphyletic. Previosu divisions palced hemiparasites in the Scrophularaiaceae,a nd holoparasites in the Orobancheaceae.
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What did phylogenetics equencing reveal about hemi- and holoparasites?
They are all monophyletic,a nd should be classed as a family, along with the autotroph Lindenbergia. Parasitism evolved only once in the lineage.
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Why were endoparasites erroneously grouped close to their hosts?
Horizontal Gene Transfers (HGTs) can make up a large proportion of the mitochondrial genes of parasitic plants. Close contact of the mitochondria at the host-parasite interface may have facilitated HGTs.
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What did plastid data indicate about Rafflesiacaeae?
They are derived from Euphorbiaceae.
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How large was the increase in flower diameter on the stem lineage of Rafflesiaceae?
79-fold, which represents one of the most dramatic cases of size evolution among eukaryotes.
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The more derived the parasite, …
… the greater the loss of genes.
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Gene loss shows convergence across unrelated plant groups.
These convergently lost genes are enriched in fucntions involving photosynthesis, defence and stress response, suggesting a common evolutionary pathway for parasitic plants. Especially high gene loss in Sapria (includes Rafflesia).
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What may contribute to host specificity in parasitic plants?
Multiple layers of incompatibility.
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Mycoheterotrophy
The ability of a plant to live on fungal carbon. Plants obtain photosynthates from other plants via mycorrhizal symbionts.
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Mycoheterotrophy has evolved multiple times…
… especially in monocots such as orchids.
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Levels of plant-fungal exploitation exist on a spectrum:
Fungi that steal from the plant, e.g., the honey fungus. At the other extreme, plants steal from the fungus. In-between is mutualism.
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Rhizanthella
The orchid that flowers underground. Discovered in western Australia in 1928. all known species were found by accident. Pollinated by termites, and dispersed underground by marsupials.
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Roles of Parasitic Plants
Weeds, keystone species or even future foods in a changing climate.
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Plant-Animal Interactions
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Theophrastus
Enquiries into plants.
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The basis for the radiations of animals
The resources provided by plants. Plants are primary producers that autotrophically energise the planet.
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An oak tree may host several hundred insect herbivore species.
Each of which may be utilised by 10-20 species of carnivore or parasite.
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Predation of Plants by Animals
Plants consumed by animals without benefit to the plant.
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Predation of animals by plants.
Plants attract, trap and digest animal prey. E.g., carnivorous plants.
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Pollination by Deception.
Plants dupe animals with olfactory or visual deception into pollinating them with no benefit to the animal. E.g., bee orchids, sapromiophily.
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Symbioses between plants and animals.
Species-specific plant-animal relationships. E.g., pollination, seed dispersal and completion of lifecycles. Myrmecophytes.
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Sapromiophily
Plants that mimic odours of rotting to attract flies as pollinators. The flies are looking for a place to lay their eggs.
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Inflorescence
Not one flower, but many small flowers, as have all the Asteraceae.
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Helicodiceros muscivorum (dead horse arum)
Found in the Balearics, where there are lots of dead gulls. Has a hairy spathe, a ring of male flowers at the top, a ring of sterile flowers/spines then a ringe of female flowers at the base.
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How is H. muscivorus pollinated?
The female flowers are cross-pollinated by the pollen brought by the flies. Overnight, the female flowers are no longer receptive to avoid self-fertilisation. The flies try to escape, but can't as they slip off the spines. The male flowers then produce pollen, so teh male and female flowers are also separated temporally.
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The flies don't benefit, so how is sapromiophily mainateained evolutionarily?
Flies reproduce so rapidly, and have such a strong drive to find a place to lay their eggs.
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What are the compounds that mimic the smell of rotting flesh?
Oligosulphides.
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How many visits do flies make to carcasses vs. dead horse arums?
The same number. Composition of volatiles from flowers and carcasses were so similar that pollinators respond in the same way to chemicals from both sources.
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How was the role of oligosulphides revealed?
Oligosulphides are only produced on the first day of flowering. When these compounds were artificially restored, the flowers became attractive to the flies again.
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Sapromiophily evolved to exploit insects as unrewarded pollinators. How was this demonstrated?
Using electro-antenna-graphic detection.
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Lizards thermoregulate on H. muscivorus flowers.
Lizards eat the flies and disperse seeds.
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Sapromiophily has evolved…
… convergently multiple times across the plant kingdom. Different plants emit different groups of compounds, e.g., some smell like dung.
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Rafflesia
Exhibits sapromiophily.
197
Why do some plants attract flies?
In some environments, sapromiophily is better than producing carbohydrate-rich nectar to attract bees.
198
Epipactis helleborine
Flowers in late August when wasps are abundant. Wasps pick up microorganisms when pollinating orchids that they then bring to the orchids.
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The micoorganisms on E. helleborine produce ethanol by fermentation. Why is the advantage of this?
When subsequent wasps visit the flower, they are drunk/uncoordinated, so spend more time on the flower, and struggle to remove the pollenia, facilitating cross-pollination.
200
Carnivorous Plants
Attract and capture prey with a leaf-derived trap, kill and digest prey, absorb the nutrients from the prey and benefit from the nutrients.
201
Evolution of Carnivory
Has evolved independently multiple times by convergent evolution in at least 6 major clades and mre than 600 species.
202
In what environments has carnivory evolved?
It has evolved in response to nutrient economics in waterlogged, acidic and mineral-poor conditions. It has always evolved when nutrients are scarce, usually nitrogen and/or phosphorous, because the traps are expensive to create, thus if nutrients were abundant, the plants wouldn't benefit.
203
Stereotype Trap Forms
Snap, pitfall (pitcher) and sticky.
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Convergent Evolution Among Pitcher Plants
Cephalotus, in the Oxidales order (Australia), Nepenthes, in the Caryophyllales order (Southeast Asia) and Sarraceniaceae, in the Ericales order (North America).
205
Common Features of Pitcher Traps
The peristome (rim), the pitcher chamber/vessel and the lid (for attraction and preventing dilution by rainwater).
206
The Peristome
Has extrafloral nectar glands to attract insects, and is made up of channels of cells, so the insects fall back down into the visco-elastic fluid at the bottom of the chamber. There is also a layer of fluid on the peristome surface.
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Visco-Elastic Fluid
At the bottom of the pitcher chamber. It has a drag force, so pulls the insect back down into the trap.
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Waxy Layer
On the inside of the chamber, so insects slide back down when trying to escape.
209
Givnish's Theory
It pays to invest in photosynthetically inefficient traps in environments where there is plenty of light anyway,a nd nutrients in the soil are scarce, which can be supplemented by insects.
210
Where is the leaf in a pitcher plant?
The leaf is the entire trap part. The lamina is what looks like a leaf, but is actually the lamina that evolved from the petiole to photosynthesise to compenstae for the lack of photosynthesis due to the trap.
211
Caryophyllales (Order)
6% of all eudicots. 33 families. A Venus fly trap (Dionaea), a sundew (Droseraceae) and a pitcher plant are all found in this order. Angiosperms incl. cacti and carnations. There are also non-carnivores and plants that a part-carnivores in this order.
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Carnivory evolved from a gland.
In Nepenthes, there are sunken, embedded glands that absorb nutrients from the prey.
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The Nepenthes pitcher evolved from the folding of a glandular leaf.
1. Adhesive glands. 2. Precursors to tentacles. 3. Foliar folding and marginal fusion.
214
How do sundew traps work?
Insects are asphyxiated with glue from the gland.
215
How do snap traps work?
Touching trigger hairs multiple times to exceed a threshold activates mechano-sensitive ion channels. These mechano-sensors generate an electrical signal that acts as an action potential, which activates motor cells.
216
Bio-Electrochemical Signals
Present in all plants, but are generally not noticeable. Like nerve impulses in animals.
217
Drosophyllum
Example of a sticky trap.
218
Triphyophyllum
A 'missing link' taxon with multiple leaf forms (normal leaves and sticky traps) on one plant.
219
Nepenthes gracilis
Ant-specific, raindrop-driven trap. It has evolved a unique, semi-slippery wax crystal surface on the underside of the horizontal and stiff lid. Pitchers secrete more nectar under the leaf and less on the peristome, thereby mainly directing the prey towards the lid. Utilises the impact of raindrops to flick insects into the trap.
220
Nepenthes albomarginata
A termite-specific trap.
221
Nepenthes ampullaria
Detrivore, catches leaf litter from the canopy. Mosquito larvae live in the phytotelma where they compose the leaf litter.
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Nepenthes rajah and Nepenthes lowii
Trap shrew faeces. Lost the features that make it such an effective insect trap because it's attracting mammals. Geometry aids the comfort of the shrew when it's defecating. Flattened large-scale ridges. Reduction in small-scale ridges.
223
Nepenthes hemsleyana
Geometry atttracts bats that leave droppings on the plant. At least 4 species display adaptations for mammalian faecal capture.
224
Why are there so many different shapes and forms in the Nepenthes genus?
Adaptations to differences in local prey assemblages may drive such divergence, and ultimately, speciation.
225
Myrmecophytes
Ant-plant mutualism. Plants with modified structures that host ant colonies in return for defence and/or nutrients. Evolved across ~50 families. Any predators of the plants would be attacked by the ant armies inside it.
226
Characteristics of Myrmecophytes
Domatia (structures that house the ants), extrafloral nectar (provided for the ants in exchange for nutrients the ants bring and defence) and food bodies (extra food for the ants as a reward).
227
Types of Myrmecophyte Interactions
1. Opportunistic and facultative interactions, including protection against herbivores. 2. Seed dispersal by ants attracted to elaiosomes. 3. Obligate interactions such as ant-plant symbioses. Cultivation mutualisms have evolved where plants have domesticated ants.
228
Elaiosomes
Seed-associated food bodies.
229
Fanged Pitcher Plant
Nepenthes bicalcarata. A carnivore and an ant plant. Produces swollen tendrils inside which ants live. The ants feed on excess prey caught in the pitcher. The ants have evolved to move in and out of the visco-elastic fluid.
230
Obligate Ant-Plant Interactions
Balloon-like structures in the leaves can be dissected, revealing that ants live within the plants, then they plant the seeds of the plant to establish future homes for the ant colonies. The ants then patrol their seedlings, and protect them from harm.
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The Unique Reproductive Biology of Angiosperms
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When did angiosperms diversify?
The tertiary.
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EJH Corner
"Even an orchid carries a recollection of its marine ancestry." He's referring to the gametophyte.
237
When will the alga come onto land?
450/470 mya.
238
Ferns
Homosporous. The amphibians of the plant world.
239
Water
Required for sexual reproduction in all early land plants for the motile sperm.
240
Archegonia
One of the key innovations of life on land. Evolved relatively early on.
241
Seed Plants
Major evolutionary transition preceded by the heterospory.
242
Ovule
The megagametophyte enclosed by integuments and nucellus. Not dispersed in angiosperms and gymnosperms.
243
When were seeds evolved?
In a heterosporous lineage in the Devonian.
244
Eggs
Sit inside the female gametophyte inside the archegonium.
245
Gymnosperms have no co-sexual reproductive structures.
Gymnosperms are either monoecious or dioecious.
246
There's an evolutionary drive to optimise sexual reproduction in the air, on land.
Hence, the reduced gametophyte, and reduced reliance on water.
247
Water in Angiosperms
Virtually eliminated in reproduction.
248
Water is still required in gymnosperms:
The pollen droplet that catches the pollen grain, and allows it to grow a pollen tube.
249
The Abominable Mystery
Fossilised angiosperms suddenly appeared in the modern form.
250
Angiosperms are hermaphrodites…
… with co-sexual flowers (though a few are monoecious or dioecious).
251
Androecium
Stamens altogether.
252
Stamen=
Stalk + filament + anther.
253
Colpus
Elongated aperture of the pollen grain wall.
254
The pollen grain in angiosperms can be shed in two ways by which all angiosperms can be categorised:
Bicellular or tricellular pollen grains.
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Bicellular
One round of mitosis, but still technically a gametophyte. Big cell: vegetative cell. Small cell: generative cell.
256
Tricellular
The generative cell has undergone another round of mitosis to form two sperm cells. This also happens in bicellular pollen, but after it has landed on the stigma.
257
The pattern on the outside of the pollen:
Can depend on the family, or even species of the plant. E.g., Astaraceae have a spiky pollen structure.
258
Gynoecium
Carpel + pistil.
259
Apocarpous
Free carpels.
260
Synocarpous/Connate.
Fused carpels.
261
Embryo Sac
Female gametophyte in angiosperms.
262
Synergids, Central Nuclei and Antipodal Cells
Haploid.
263
Micropyle
Pollen tube growth occurs through here.
264
Callose Plugs
Isolate the cytoplasm of the vegetative pollen tube cell. The active part of the pollen grain is at the tip.
265
The Pollen-Pistil Interaction
Cellular events on the stigma and within the style prior to fertilisation.
266
List of events in the pollen-pistil interactions:
1. Pollen capture by the stigma. 2. Pollen adhesion. 3. Pollen hydration. 4. Pollen germination. 5. Pollen tube penetration of the stigma. 6. Growth of the pollen tube towards the ovule. 7. Entry of the pollen tube into the ovule leading to fertilisation.
267
Implications of the pollen-pistil interaction:
1. Evolution of pollen discrimination systems. 2. Pollen competition.
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Evolution of Pollen Discrimination Systems
Incompatibility systems: intraspecific self-incompatibility systems and interspecific incompatibility systems.
269
Pollen Competition/Gametophytic Selection
Some pollen grains grow faster, so will be fitter than other pollen grains. This adds another lsayer of selection to the natural sele tion of the final sporophyte that is produced. 60-80% of the genes expressed in the microgametophyte are also expressed in the sporophyte, so are subject to selection in the pollen-pistil interaction.
270
When is selection more effective?
When it's working on one copy of the gene-- haploid.
271
How does the pollen tube find its way to the ovule?
Gradient of water potential, various chemical pollen tube attractants in the stigma and style and the synergid peptide signal (LURE).
272
Gradient of Water Potential
Created by the srface lipids of the stigma or pollen coat. Pollen grains are dehydrated, and stigmas are fully turgid.
273
Various Chemical Pollen Tube Attractants
E.g., TTS (Transmitting Tissue Specific Arabinogalactan Glycoprotein), GABA (Gamma-Amino Butyric Acid), chemocyanin and Le-STIG1 (cysteine-rich stigma-specific protein 1).
274
The Synergid Peptide signal (LURE)
The only method shown to be universal in all groups. Attracts the pollen tube to the ovule as a prelude to fertilisation. There are receptors in the pollen tube that bind to LURE.
275
Triploid Endosperm
2 maternal and 1 paternal, but a diploid embryo.
276
What did confocal microscopy by Higashiyama reveal?
The pollen tube penetrating one of the synergid cells, then rapidly releasing the two sperm cells. The cytoplasm is stripped from the sperm cells, one fertilises the egg and the other fertilises the two haploid central nuclei. In some angiosperms, the central nuclei are already fused.
277
The endosperm 2m:1p ratio is critical for seed size.
If you manipulate that by adding more maternal genome, the seeds get smaller. If you add more paternal genome, the seeds get larger. This represents the conflict between the two genomes.
278
Ovule -->
Seed.
279
Ovary -->
Fruit.
280
What % of everything humans consume comes from seeds?
0.7
281
Nuclear Endosperm
The most common form. Fertilisation followed by repeated nuclear-free divisions. Liquid endosperm (lots of nuclei, but no cell walls), e.g., coconut milk. If a cell wall forms. It will do so later, e.g., cereal and beans.
282
Cellular Endosperm
Fertilisation followed by normal cell divisions with cell wall formation, e.g., Petunia, Datura and Impatiens.
283
Helobial Endosperm (Rarest Form)
A cell wall is laid down between the first two nuclei, after which one half develops cellular endosperm and the other half nuclea, e.g., Muscari, Saxifraga, Echium and Asphodelus.
284
Progenesis
The angiosperm sporophyte develops from 7 cells with 8 nuclei, instead of the multicellular gametophyte as in gymnosperms.
285
Integuments
Harden to become the seed coat.
286
Various Parts of the flower Around the Seed
Develop into the fruit.
287
Why is there such a diversity of fruit?
Fruit evolved to attract frugivores.
288
Guavas
The fruit develops from the ripening, swollen ovary.
289
Plants want to get the fruit through the animal to prevent the digestion of seeds.
Hence, many fruits contain a laxative, especially in figs.
290
In gymnosperms, there's more investment in the gametophyte.
It's multicellular, and packed with nutrients. Angiosperm seeds utilise maternal resources more efficiently than in gymnosperms. They delay investment of nutrients until after fertilisation
291
292
Angiopserm Mating Systems and Pollination
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294
Mating (Breeding) System
The way in which a group of organisms is structured in relation to its reproductive behaviour.
295
Why are the majority of flowers co-sexual?
To optimise animal pollination as a pollinator can bring in and take away pollen in the same visit. Sessility has driven the evolution of co-sexual flowers.
296
Darwin
Wrote 8 books on plant biology, particularly on plant-animal interactions.
297
Primular vulagris and cowslips
Their mating systems were studied by Darwin. Primulas have two morphs: a pin and a thrum, 50% of individuals belong to each morph.
298
Pistil
Female organs of a plant. Stigma + style + ovary.
299
Pin
The long-styled morph, where the pistil is prominent in the corolla.
300
Thrum
the short-styled morph, where the stamens are prominent in the corolla.
301
What was the reason for the pin and thrum morphs in Primula, according to Darwin?
To increase the likelihood of outcrossing.
302
Darwin manipulated pollen, so that he selfed each morphotype. What did this reveal?
Legitimate and illegitimate unions. He identified a physiological discrimination system that distinguishes between the pollen of the two morphs.
303
Legitimate Unions
Thrum to the stigma of a pin gives seeds, and vice versa.
304
Illegitimate Unions
Pollinating pin with pin, or thrum with thrum, does not give seeds.
305
Mating Systems
Structure and physiological features of the flower. Extremely diverse in angiosperms.
306
Pollination Systems
Structural features of the flower, or the inflorescence-- adaptations to pollination. There is overlap between mating and pollination systems.
307
Factors influencing mating system evolution:
Immobility, inbreeding depression, reproductive asssurance and optimal allocation of male and female reproductive effort.
308
Immobility
~96% of angiosperms are hermaphrodite (flowers are co-sexual or unisexual, e.g., monoecious).
309
Inbreeding Depression
A reduction in fitness due to selfing or mating with a closely-related plant. One of the strongest selective pressures for outcrossing, hence most angiosperms outcross albeit to different extents.
310
Reproductive Assurance
Driver of selfing. If mates or pollinators are scarce, it is better to reproduce asexually (apomixis) or to self to produce offspring, rather than no offspring at all.
311
Optimal allocation of male and female reproductive effort:
Particularly important in the maintenance of sexual polymorphisms such as dioecy, gynodioecy, etc..
312
Dioecy
Individuals are either male or female throughoit their lives.
313
Gynodioecy
Very rare. Both females and hermaphrodites exist in the population.
314
Cleistogamy
Flowers that don't open, but are self-fertilised.
315
3 Extremes to the Triangle of Mating System Interfaces
Obligate outbreeding, autogamy/inbreeding and asexuality.
316
What influences which vertex of the triangle is favoured?
Inbreeding depression and reproductive assurance as well as local pressures.
317
The majority of plants with co-sexual flowers outcross, but…
… with co-sexual flowers, self-pollination is always possible.
318
What can increase the likelihood of selfing?
Bees are not always precise, and large, nectar-feeding bats. Hence, the evolution of pollen incompatibility systems involving chemical signals.
319
Adaptations to avoid self-fertilisation:
Dichogamy, herkogamy, dicliny and self-incompatibility.
320
Dichogamy
Separation of sexual organs in time: protandry or protogyny. The male and female phases are de-synchronised in the same flower to decrease the risk of selfing.
321
Protandry
Stamens mature before the carpels/pistils.
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Protogyny
Carpels/pistils mature before the stamens.
323
Herkogamy
Common in orchids. Separation of sexual organs in space, e.g., style length polymorphisms such as distyly and tristyly, and bizarre flowers.
324
Dicliny
sexual polymorphisms: plants are male or female (dioecious), or unisexual flowrs on the same plant are male or female (dioecious), or combinations of unisexual and co-sexual plants (e.g., gynodioecious), or unisexual and co-sexual flowers on the same plant (e.g., gynomonoecious).
325
Self-Incompatibility
Plants are able to recognise and reject their own pollen.
326
Pre-Zygotic Barrier
Incompatible pollen is recognised or rejected before it reaches the ovule. It's a haploid-diploid interaction as it occurs between the pollen tube and the female part of the sporophyte. Depending on whether it is self or non-self, the pollen is rejected or encouraged actively.
327
What % of hermaphrodite angiosperms use self-incompatibility?
~65%.
328
The S Locus
The most polymorphic genetic locus in angiosperms.
329
By what is self-incompatibility usually controlled?
A single genetic locus, the S locus, with multiple alleles, e.g., S1, S2, S3 etc..
330
To what is the S locus equivalent?
The mating system loci in fungi, or the mating types in algae.
331
With what is the S locus analogous?
The major histocompatibility system as both are highly genetically polymorphic.
332
The S locus is highly polymorphic:
Populations maintain ~40 S alleles, but some populations of clover can have ~130 alleles!
333
What maintains this level of polymorphism?
Negative frequency-dependent selection: an allele that is rare in the population is advantageous because the carrier can mate with lots of other individuals in the population with different alleles. This means rare alleles rarely go extinct, and newly-evolved alleles are at an immeditae selective advantage.
334
If the alleles at the S locus in the pistil and pollen genotypes are different, …
… seeds are set, and they're compatible.
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If the alleles at the S locus in the pistil and pollen genotypes are the same, …
… seeds are not set, as they are incompatible.
336
Two main types of genetic self-incompatibility (SI):
Gametophytic SI, and Sporophytic (SSI).
337
Gametophytic SI
The incompatibilty phenotype of the pollen is determined by its own haploid genome. S alleles are co-dominant in the pistil.
338
Sporophytic SI
The incompatibility ohenotype of the pollen is determined by the diploid genome of its parental plant (sporophyte). S alleles exhibit dominance in the pistil and in pollen. Eevn though the pollen is haploid genetically, it behaves with a diploid phenotype in terms of incompatibility. E.g., from an S2, S2 individual, all the pollen will be carrying the proteins associated with S1 and S2.
339
There tends to be the same type of incompatibility system in…
… the same family.
340
Families with Gametophytic SI
Solanaceae (potato family), Rosacaeae, Plantaginaceae, Campanulaceae, Papaveraceae (poppies) and Poaceae (grasses).
341
Families with Sporophytic SI:
Brassicaceae, Asteraceae, Convolvulaceae, Betulaceae, Caryopphyllaceae and Malvaceae.
342
Pollen tube behaviour in GSI:
The pollen tube tends to grow a relatively long way before inhibition.
343
Pollen tube behaviour in SSI:
The pollen tube growth soon after, or even before, germination.
344
Prevalence of Distyly
Present in 155 genera from 25 families.
345
Distyly in Primula
388/426 species of Primula exhibit distyly.
346
Primula has SSI, but uses the minimum number of alleles for an incompatibility systems tof ucntion.
One allele is completely the domiannt, whilst the other is completely recessive. Pin: ss. Thrum: Ss.
347
Distyly mirrors sex determination:
50% are ss (pins), and 50% are Ss (thrums).
348
The heteromporhic S locu is a supergene.
It controls SI and other morophological charcateristics, e.g., style length, stamen position.
349
What promotes pollination by lock and key in Primula?
Different sizes of epidermal cells, and shapes of pollen scultpure, on the pins compared to thrums. In pin stigmas, there are large, domed epidermal cells, and smaller sculptures on the pollen grain. The opposite is the case on the thrums.
350
Arabidopsis
A habitual selfer, like 20% of angiosperm lineages.
351
What % of angiosperms are able to self-fertilise?
35-40%.
352
Autogamy/selfing:
The balance shifts away from maintaining genetic variation towards producing offspring within the plants' lifespans.
353
Evolution of Selfing within Outcrossing Groups
Common across all angiosperm lineages.
354
Mixed Mating Systems
Some populations will be outcrossing, whilst others are selfing.
355
Genetic consequences of selfing.
25% of offspring from a heterozygous parent will carry the recessive allele. This offspring is then a candidate for inbreeding depression. The amount of gentically-determined variation will decline with time.
356
What drives selfing?
Reproductive assurance.
357
Why don't habitual selfers suffer from inbreeding depression?
Deleterious alleles are purged, dominant alleles are fixed in homozygotes, and habitual selfers are hmozygous at most loci.
358
What happened when the obligate outcrosser Senecio squalidus was forced to self?
This created a range of mutants, e.g., one without vacsular tissue that flopped over, or one that produced leaves instead of flowers. The converse of that is that there are indivisuals concentrating the dominant alleles during this process of increasing homozygosity. these individuals survive, but the mutants don't.
359
Deleterious/recessive alleles are purged:
The less-fit individuals carrying the recessive alleles die out. Individuals that are adapted to the environment remain with homozygous dominant alleles.
360
Advantages of Selfing
Removes male expenditure and costs of outbreeding, e.g., producing large flowers or lots of nectar, and optimises reproductive assuranec when pollinators are scarce or unreliable, plants are pioneers or colonisers (Baker's Law), or when populations pass through bottlenecks.
361
Baker's Law
Small populations are more likely to evolve selfing.
362
Eichhornia paniculata
Brazil= outcrossing population. Nicaragua= selfing population. Once selfing was establihsed, selection favours reduction in flower size and pollen and nectar production, and a disappearance of adaptations for herkogamy, dicliny and dichogamy. In the outcrosser, heterostyly is an adaptation to outcrossing that is lost when selfing. The selfers hae homostyly (the stigma and stamens are of equal height).
363
Disadvantages of Selfing
Decreases genetic diversity, plants cannot adapt to changing environmental conditions and it's an evolutionary 'dead end'.
364
Why are branches of selfing lineages on a phylogenetic tree shorter?
The fixed homozygotes created by purging in selfing can't really adapt to a changing environment, so die.
365
Typical Properties of Plants in Selfing Populations
Annual, fast-cycling plants that get seeds made under difficult conditions, and survival of seeds, e.g., in sand dunes, ensures genes continue to the next generation.
366
Apomixis/Agamospermy
The production of fertile seeds in the absence of fusion between gametes.
367
Where is apomixis common?
In Rosaceae. Blackberries are the product of apoxmixis.
368
Demonstrating Agamospermy in the Dandelion (Taraxacum officinale)
Cut the dandelions to emasculate the bud by cutting off the stamens, and seeds are still produced. These agamospecies/microspecies are good 'biological species' as all offspring are clones, so are reproductively isolated.
369
Advantages of Agamospermy
Reproductive assurance, avoids cost of meiosis, transmits 100% of the mother's genes to the offspring, fixes well-adapted genotypes, and it's particularly common in hybrids and polyploids as it frequently maintains or fixes hybrids and polyploids.
370
Disadvantages of Agamospermy
No recombination, so Muller's Ratchet occurs. Unable to recombine advantageous mutations. Very narrow niche tolerance. Inability to adapt, so it's an evolutionary 'dead-end'.
371
Gametophtic Agamospermy
The embryo sac is diploid. There is diploid devlopment of the female gametophyte, then the diploid egg that is entirely maternal turns into the embryo. In some Rosaceae, you still need fertilisation for the two central nuclei to form an endosperm, so pollination is still required. Or in dandelions, the diploid central fuse to give a tetraploid endosperm.
372
Sporophytic Agamospermy
The embryo sac is haploid. The female gametophyte develops normally, there's pollination and fertilisation, and then another diploid cell from the nucellus that encloses the gametophyte invades, and takes over the embryo. This will then have the genetic form of the female that produces it. The sexual embryo aborts, and the diploid embryo forms from one or more cells of the nuclelus.
373
Why are agamospermous GM crops being engineered?
They reduce/restrict transgene flow from GM crops into natural relatives.
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Pollination Mechanisms
376
377
The Diversity of Flowers and Inflorescence
Reflects diverse adaptations to pollination.
378
Orchidacaeae are the largest family of flowering plants.
There are 25,000-30,000 species.
379
What is the key to the abominable mystery?
The transition from the unisexual cones of gymnosperms to the co-sexual flowers of angiosperms.
380
Honey Guides
Feature of orchids that inidcates that nectar is produced.
381
Where is nectar often held, e.g., in orchids?
In a spur.
382
Darwin's study of purple orchids:
Put a pencil into the opening of the orchid, so the pollinia gets stuck on the end of the pencil.
383
The tropic movement of pollinia:
Pollinia have adhesive pads, so when they are first stuck on, they are vertical. They then undergo a tropic movement, so are moved 90° into the prime position to deposit the pollen on another plant.
384
Orchid pollen is held in a pollinia.
Pollinia sit on a receptacle, and are analogous to mobile stamens.
385
Why is all the orchid pollen shed at once?
The pollinia are shed.
386
What polination syndromes did Darwin document?
Bee pollination of flowers, flowers that have long corolla tubes or long nectar spurs attract butterflies with their long probooscises and plants pollinated by moths are often white, and intensely scented.
387
Adaptations to animal/biotic pollination:
Primary attractants (rewards), and secondary attractants (advertise the presence of a reward).
388
Primary Attractants
1. Pollen-- rich in protein, starch and fats. 2. Nectar-- sugary exudate from nectaries, also amino acids and fats. 3. Oil-- fat oil from elaiophores, e.g., Orchidaceae, Schropulariaceae. 4. Protection and a brood-place, e.g., Calluna and thrips; figs and fig wasps. 5. Sexual attraction, particularly Orchidaceae.
389
Secondary Attractants
1. Odour-- night-flowering plants, 'rotting meat' flowers; sex pheromones. 2. Visual attraction-- colour, shape, UV, honey guides; reflection. 3. Temperature-- heliotropic flowers in colder climates. 4. Motion-- poorly understood; flickering of large inflorescences.
390
Insects can see in UV.
This often provides a contrast between the petals and the centre (where the nectar is).
391
What was recently identified as the pollinator of the Madagascan orchid?
Crickets.
392
Pollination Syndromes
Insects, vertebrates and abiotic syndromes.
393
Insect Pollination Syndromes
1. Beetles (Cantharophily). 2. Flies (Myophily). 3. Bees (Melittophily). 4. Wasps. 5. Butterflies (Psychophily). 6. Moths (Phalaenophily). 8. Ants.
394
Vertebrate Pollination Systems
2. Birds (Ornithophily). 2. Bats (Chiropterophily). 3. Possums. 4. Others such as mice, lemurs and lizards.
395
Abiotic Pollination Syndromes
1. Wind. 2. Water.
396
Water-Dwelling Angiosperms
Have adaptations for water-pollination, e.g., 'boats' to transport pollen, e.g., seagrass.
397
Length of Nectar Spurs
Correlated with the elngth of the tongue/proboscis of the pollinator.
398
Madagascan Star Orchid (Angraecum squalidus)
Darwin believed it was pollinated by a moth due to its long nectar spurs, white colour and intense scent at night. Contemporary entomologists didn't believe him.
399
In 1909, what was discovered that proved Darwin correct?
The long-tongued hawk moth, Xanthopan morganii praedicta, and Morgan's sphinx moth.
400
Why aren't all pollination syndromes so specific?
The relationship is fragile as the specialist pollinator could become extinct.
401
Hoverflies
Common pollinators of daisies.
402
Generalist Pollination systems
Tend to involve large, open flowers. Common in the carrot (Apiaceae) and daisy (Asteraceae) families.
403
Stebbin's Most Effective Pollination Principle
A plant should specialise on the most effective and/or most abundant pollinator, when pollinator availability is reliable. Generalisation is favoured when the availability of even the most effective pollinator is unpredictable from year-to-year.
404
Specialisation
There are lots of pollinators to facilitate outcrossing. Pollinator-rich regions: tropical rainforests, sub-tropics, Mediterranean and warm temperate.
405
Generalistion
Pollinator-poor regions: boreal, alping, cold temperate and deserts. Pollinators are scarce, so apomixis and selfing are more common in these regions.
406
The Genus Dracula
Orchids in this genus are all monkey-faced.
407
What % of the pollination mechanisms in orchids involve cheating?
Well over 50%. up to 60%.
408
Pollination in Orchidaceae
1. Nectar rewards. 2. Traps. 3. Deceit, either by mimicking female insects, or nectar reward flowers. 4. Provision of a brood hole, or resting place.
409
Mimicry of Nectar Reward Flowers
E.g., Anacamotis morio resembles Orchis anatolica, but unlike the latter, the former doesn't produce nectar-- a nectar cheat. In A. morio, the insects spend longer searching for the reward, wheras in O. anatolica, the insects sometimes reach the nectar before the pollinia ate deposited. this is only possible because the cheats are so rare.
410
What do monkey-faced orchids mimic?
The gills of fungi to attract fungus gnats tahta re looking to lay their eggs. The orchid also produces a fungus-like aroma.
411
Bee Orchids
Ophrys: 160 species.
412
Why are the speculums of bee orchids only visited by males of the species Campsoscolita ciliata?
Males attempt to mate with the flower then get pollinia stuck on its head because these flowers produce a scent that is almost chemically identical to the scent produced by the female bees. The first-releaser is olfactory.
413
Orchids have diversified by mimicking different pheromones.
Hence, there's a 1:1 relationship between the orchid and its pollinator.
414
Beyond scent, how else do bee orchids attract their pollinators?
The iridescent speculum resembles the wings of the female. The furriness of the bellum, a petal-like structure at the base, is a tactile stimulus.
415
Ophrys orchids produce a super-optimal response:
When given the choice between a flower and a female, the bee chooses the flower!
416
Ophrys sphegodes dummy
Induces pseudocopulatory behaviour in male Andrena nigroaenea. The false pheromone is extracted from the orchid. Material is soaked in it, and put on a stick. The pollinator then tries to mate with it.
417
Ophrys Orchids in the UK:
Late and early spider orchids, bee orchids and fly orchids, but they are more diverse in the Meditteranean and North Africa.
418
Pollination in Figs
There is a clear symbiosis between the fig and its Agaonid wasp (fig wasp) pollinator-- co-evolution.
419
Classification of the Fig
Family: Moraceae, that includes cannabis, jackfruit/bread fruit, mulberries and hops. Genus: Ficus, one of the largest angiosperm genera. 800-1,000 species.
420
Cultigens
Edible figs don't grow in the wild; they only grow when cultivated.
421
Female fig wasps have pouches.
Found on the underside of the thorax. Can carry 2,000-3,000 pollen grains.
422
Figs have synconia:
When the green syconia are cut open, flowers are found inside.
423
3 Types of Flowers Found in Fig Syconia
Neuter flowers/short0styled female flowers that eventually become galls, long-styled female flowers and male flowers.
424
What has been used to observe wasps inside the fig synconium?
Observational windows, or fibre-optic cameras.
425
Fig wasps exhibit sexual dimorphism:
the male is a smaller, more muscular version of the female. The males have muscular legs, no wings, poorly-developed antennae and are virtually blind. Females have wings to mate with different males in fig synconia.
426
Female fig wasps deliberately pollinate female and neuter flowers.
pollination is deliberate as the female loads her pouches with pollen after leaving the synconium, in which she mated. The muscular males dig a hole for the female to let her out post-mating. She lays her eggs in another synconium-- the brooding syconium. To get into the syconium, She forces her way through the narrow ostiole that impedes the entry of other insects. She may lose wings, antennae, or even a leg. After oviposition, she uses her forelegs to remove the pollen from the pouches, and place it on the stigmas. Then she dies because she can't get out.
427
Why can the female fig wasp only get effective oviposition on the short-styled female flower/neuter flower?
In the long-styled flowers, the ovipositor doesn't reach.
428
How many different wasp species may be contained within the syconium of Ficus sycomorus?
5
429
Parasites in the Fig System
Parasites with long ovipositors deposit their eggs in a random way through the side of the syconium to exploit the fig-pollinator system. When the grubs of the parasite hatch, the grubs of the legitimate pollinators fight them, and usually the legitimate pollinator grubs win.
430
Examples of Parasites of the the Fig Wasp System
In Ficus sycomorus, Ceratosolen arabicus is the legitimate pollinator that fights back against Sycophaga sycomori that enters the syconium, and lays its eggs on the female flowers with its long ovipositor. There are 3 other wasps that don't enter the syconium, but have lomg, piercing ovipositors to lay their eggs on the neuter flowers from the outside.
431
Fig Syconia are Microcosms
The dead wasps in the fig syconia are food for nematodes inside the fig. When the nematodes die, they become food for the Pseudomonas bacteria in the fig syconia.
432
433
Mammals: Origin and Diversity.
434
435
Synapsids
Diverged from the amniotes, which diverged from the Sarcopterygians.
436
Non-Mammalian Synapsids (Mammal-like Reptiles, Extinct)
Pelycosaurs, Therapsids and Cyconodonts. All diverged before extant mammals.
437
When did mammals originate?
In the Permian, pelycosaurs and therapsids originated. There was a radiation of mammals with homogenous body forms in the Mesozoic, specifically Triassic.
438
Tertiary Radiation
When the dinosaurs became extinct, there was an explosion in body form.
439
Megafaunal Extinction
Occurred in the Tertiary.
440
Archeothyris
One of the earliest non-mammalian synapsids (pelycosaur). It had a large temporal fenestra.
441
Temporal Fenestra
A bilaterally symmetrical hole in the temporal bone through which jaw muscle passes through. Defining feature of synapsids. A larger temporal fenestra indicates a greater volume of jaw muscle, so more food is eaten per day, and metabolic rate is higher.
442
Pelycosaurs tended to be carnivorous, but some were herbivorous.
Herbivores had blunte teeth, and a broad gait toa take in lots of vegetation.
443
Dimetrodon: a carnivorous pelycosaur.
Most derived pelycosaur. Arched palate, which is the first step towards separation of the mouth and nasal passages, which in turn, indicates higher metabolism and faster movement by enabling simulatenous eating and breathing.
444
Dimetrodon had elongated neural spines into a sail.
This was likely for temperature regulation, not display, as there was no sexual dimorphism.
445
Therapisds
More derived than pelycosaurs. Appeared in the fossil record as 9 groups in the late Permian, but this was likley preceeded by a slower ardiation in the early Permian. Found mainly in Gondwana. Increased metabolic rate. Flexible neck for differences in locomotion.
446
Therapsids had a trough in the roof of the mouth, instead of an arched palate.
This indicates the evolution of adedicated airway, separate from the rest of the oral cavity.
447
What does differentiation in teeth type in therapsids indicate?
More ecological variation.
448
Titanophoneus
A carnivorous therapsid with more slender limbs, more freedom of movement in the shoulder joint and a larger stride than pelycosaurs.
449
Gorgonian Therapsides
carnivorous. Like modern big cats. Differentiation of teeth, and the hindlegs provide speed.
450
The Advanced Cyconodont
Very derived. Smaller body size than most of the other Therapsids. Gave rise to mammals. Had an enlarged infraorbital foramen.
451
What does the enlarged infraorbital foramen suggest?
A highly innervated face, perhaps with a sensitive muzzle or whiskers.
452
Teeth Specialisation
Broader ecological range.
453
Loss of Lumbar Ribs
Suggests a diaphragm, and greater respiration rates.
454
Limb position
Limbs come underneath the body, instead of the broad gait, for flexibility.
455
Evolutionary Trends in Synapsids
1. Larger temporal fenestra. 2. Greater teeth specialisation. 3. Development of a bony secondary palate. 4. Limb position. 5. Dual gait locomotion. 6. Loss of lumbar ribs. 7. Increasing ability to regulate internal temperatres and environments.
456
Cenozoic
The age of mammals, but 2/3 of mammalian history was the radiation of Mesozoic mammals.
457
Feature of the Earliest Mammals
Tiny, derived features of the skull reflecting the large brain and inner ear. Evolution of lactation and suckling. Hair. Specialised Harderian gland.
458
Why might the earliest mammals have evolve dfur?
For insulation due to their high surface area : volume ratio.
459
What is the function of the Harderian gland?
To produce oil. The mammal then wipes the oil on its body to insulate the fur.
460
Why did mammals radiate after the dinosaurs became extinct?
There was unlikely to be competition between the mammals and the dinosaurs, but the dinosuars did prevent mammals entering a variety of niches. These niches became available after the mammals became extinct.
461
Megafauna
Giant Irish elk (2.5m tall), Smilodon, Megatherium and Phoberomys (a 700 kg rodent).
462
Why did all these megafauna become extinct?
Humans became more efficient hunters.
463
Mammalian Charcateristics
Endothermy underpins a lot of the other characteristics. Reproduction, lactation, hair, high blood pressure, high O2 uptake, high metabolic rate, water regulation (the loop of Henle), improved locomotion and improved sensory systems.
464
Why can't a high level of homeostasis be achieved by the juvenile of a small mammal?
Their surface area : volume ratio is too high, and it takes time to develop the control systems, e.g., in the brain. Hence, the mother provides an externally-controlled environment where temperature, nutrients etc. are controlled.
465
Lactation allows…
… mammals to separate the time of year from breeding. Reproduction can happen at any time of the year. Young can be born at a relatively undeveloped stage, and cared for outside the uterus,
466
Occlusion
Teeth fit together precsiely.
467
What consequences did the evolution of lactation have?
Newborns don’t need teeth,s o there was shift from the continual replacemnet of teeth to diphyodonty. Thus, occlusion could evolve, which facilitated the diversification of early mammals to exploit a greater range of food and feeding strategies than seen in any other vertebrate group.
468
The Ability to Suckle
Uniquely mammalian. Fleshy seals formed agaisnt the boy, hard palate with the tongue and the epiglottis, isolating the functions of breathing and swallowing. These cahnegs in the palate bone structure are only in the most derived cynodonts.
469
Facial Muscles
Charcteritic of mammals, eventually enabled facial expressions.
470
Hair
For insulation, camouflage, sensation via vibrissae (whiskers, key to nocturnal mammals) and communication.
471
Mammalian Sensory Systems
Large brains and neocortex. More reliant on hearing and olfcation, and less on visual systems, than other amniotes.
472
Why is visual sensitivity mor eimportant than acuity for mammals generally?
Mammals evolved as nocturnal. Cones in the fovea enable acute vision in one small section of the retina.
473
Non-Cursorial Locomotion
Basic mode of mammal locomotion. The hindlimb, larger thena the forelimb, provides all the thrust. The pelvic girdle is fixed rigidly to the sacral vertebrae, with the foot as an extra extensible unit.
474
Non-Cursorial Mammal Locomotion vs. Reptile Locomotion
Non-cursorial locomotion is neither faster nor more efficient than that of a similar-sized reptile.
475
Joint Formation
Constrains mammalian locomotion capabilities.
476
Fossorial Locomotion (Digging)
Limb bones are short and stout with muscle attachments well away from the joints, providing powerful, but slow movement of the limbs.
477
Cursorial Locomotion (Running)
E.g., horses have elongated limbs. Power comes from the muscles at the top. Tendons give flexibility and additional propulsion.
478
Gaits Evolved
E.g., walk, trot, canter and gallop in horses. This gives extra flexibility over different terrains.
479
Fast Big Cats
Have extension and retraction across the spine, where there's lots of muscle.
480
Specialised Forms of Locomotion
Saltatory (jumping), arboreal (e.g., sloths, gibbons), knuckle walking in gorillas, bipedality in humans, aerial (e.g., the flying lemur, but the only mammals capable of true flight are bats) and aquatic mammals, e.g., seals and whales.
481
Of what is much of mammlian diversity a reflection?
The isolation of different groups on different land masses, and cliamte change in the Cenozoic resulte din different habitats and associated adaptations, e.g., grassland.
482
3 Main Lineages of Extant Mammals
Monotremata, Marsupialia and Placentalia. The manner of reproduction is the greatest difference between them.
483
Where do Montremes occur today?
Australia and New Guinea.
484
Monotreme Reproduction
They lay eggs (ancestral). Young hav a reptile-like egg tooth to escape from the egg.
485
Cloaca
The single hole used by monotremes for both reproduction and excretion.
486
Monotreme Development
The small egg develops to form a rapidly dividing outer layer that envelopes the egg. The uterus secretes a double-layered porous shell about the embryo. Unlike reptiles and birds, the egg then grows. Meroblastic cleavage.
487
Meroblastic Cleavage
The early divisions are incomplete. The same as in birds.
488
The mode of sex determination in the platypus is unclear.
It has multiple sex chromosomes. The male has 5X and 5Y.
489
The Maternal Immune System
Protects the embryo in placental mammals.
490
Why does the platypus have an enormous genome?
The maternal immune system can't protect the embryo when it's in an egg, so the genome has a large expansion of natural killer cell proteins, certain antimicrobial peptides and other components of the innate immune system.
491
The platypus is one of only a few venomous mammals.
These venoms came by duplication of genes for other functions, and subsequent divergence. The amles have a venomous spur on the heels of their hindlegs, perhaps used in premating combat, or for defence.
492
The platypus bill is filled with electroreceptors for electrolocation.
It can determine the direction of an electric source by comparing differences in signal strength across the sheet of electroreceptors.
493
Echidnas
Have very sticky tongues. Use fossorial digging to burrow through ants' nests.
494
Where do the 500 or so specie sof Marsupails occur?
Australasia and South America, which were once part of the same continent.
495
Marsupial Development
The thin shell membrane is added after fertilisation, then retained trhoughout most of gestation to protect from the maternal immune reaction. The egg sac expands, forming a bilaminar blastocyst. The mesoderm inavdes and vascularises the embryo to create a trilaminar part of the embryo sac. The yolk sac wall has lots of mitochondria nd villi for uterine secretions.
496
Kangaroo Neonates
Very underdeveloped, e.g., underdeveloped CNS, facial muscles etc., when they are born. The only thing fully developed is their sense of smell to climb towards the nipple. They use tehir front claws as a holdfast, and the shoulder arch aids climbing by acting as a brace, but constrains later development.
497
Egg Size
Intermediate between monotremes and placentals.
498
Marsupials are given milk for longer, and its composition changes as the marsupial develops.
In the milk, fats increase over time. Oligosaccharides decrease, and are replaced with monosaccharides over time. Proteins increase slightly over time.
499
Examples of Marsupials
The Marsupial mole, sugar gliders, possums, opossums and Tasmanian devils (link to BaP).
500
Placental Development
The eggs are even smaller than marsupials'. No shell membrane at any time. The allantois expands into a large placenta.
501
Larger Live Young
Mean placentals have a larger opening at the base of the pelvis than other mammals.
502
Placental Sensory Systems in Water
light has been readily absorbed, visibility is poorer and there's turbidity. Sound travels further and faster than light.
503
Vision in Water: Elephant Seals.
Elephant seals feed at depths of 300-700m, so have eyes that adapt to poor light faster than any mammal tested. Nonetheless, they must still rely on other senses at the bottom of their feeding range.
504
Harbour Seals
Use vibrissae to track the hydrodynamic trails left by fish. When tested by tracking a submarine, the harbour seals relied solely on the whiskers as auditory cues were removed with headphones.
505
Echolocation: Dolphins.
Dolphins send out clicks, concentrated by the melon, then it bounces back, and the dolphin detects the perturbations.
506
Humpback Whales
communicate via sound. Have local dialects in different populations.
507
Underground Sensory Systems: the Star-Nosed Mole.
Has eleven rays moved by tendons attached to facial muscles. Each ray contains hundreds of mechanoreceptive Elmer's organs innervated by the infraorbital nerve.
508
Bat Echolocation
Has evolved multiple times indepndently in different bat lineages by convergent evolution. It also evolved in shrews and dolphins. Call features, such as frequency, bandwith, duration and pulse interval, are all related to ecological niche rather than phylogeny.
509
Co-evolution Between Long-Eared Bats and Moths:
The long-eared bat listens for moth movement, filtering out other sound. It uses echolocation to navigate obstacles, then stealth mode to catch the moth. The moths engage in an evolutionary arms race: Aartiid moths hear the clicks of echolocation, then proudce their own sounds, using a tymbal organ on the metathorax, to disturb the sensory systems of the bat.
510
511
What is a mammal? Structure and Function: Homeothermy.
512
513
Class Mammalia
A group of animals with backbones, and bodies insulated with hair, which nurse their infants ith milk and share a unique jaw articulation.
514
How many bones did mammalian ancestors have in the lower jaw?
3/4, some of which have migrated to make the ossicles.
515
Characteristics of Extant Mammals
A single bone in the mandible, two occipital condyles, long bones with eiphyses for determinant growth, four-chambered heart with left aortic arches, dentition, the middle ear with 3 ossicles, epidermis with hair, vivparous (except monotremes), mammary glands and tehy are endothermic with a higher metabolic rate (central to the other characteristics).
516
The Smallest Mammal:
At ~2g, it's the bumblebee bat/Kitti's hog-nosed bat.
517
The Largest Mammal:
The Blue Whale may have a mass of up to 100 million times as much as Kitti's hog-nosed bat.
518
Some Mammals Are Long-Ranging:
The African Wild Dog may roam a home raneg of up to 2,500 km^2.
519
Other Mammals Are Sedentary:
Naked mole rats never leav eteh burrow, and have 28 pups per litter!
520
Some Mammals Are Slow-Developers:
Elephants take 22 months to gestate a calf, and live 70 years.
521
Some Mammals Are Short-Lived:
The male of the brown atechinus never sees a second season, and dies before the first and only litter it has fathered is born.
522
In the subclass Prototheria, there is the order…
… Montremata: they diverged first, and are egg-laying. 5 species in 2 families in 3 genera.
523
When did the subclass theria diverge?
At the end of the Triassic. They are the live-bearers, so exclude the Monotremata.
524
The Infraclass Marsupialia
(Formerly Metatheria). Diverged 70 mya. In Australasia and South America.
525
How many superorders of Placentalia are there?
Afrotheria, Xenarthrans, Euarchontoglires and Laurasiatheria.
526
Afrotheria:
E.g., dugongs, hyraxes and elephants. Diversity of forms.
527
Xenarthrans
E.g., anteaters, sloths and armadillos. Mostly South and Central America, and some in North America.
528
Euarchontoglires
Lagomorphs, tree shrews, colugos, primates and rodents.
529
Laurasiatheria
Carnivores, pangolins, shrews, bats, moles, hedgehogs, whales, dolphins and ungulates.
530
What does endothermy allow mammals to do?
Live in cold environments and be active at night.
531
Basal Metabolic Rate
Metabolic activity required for minimal resting lifestyle with no spontaneous activity, digestion or stress.
532
Mammals have high basal metabolic rates:
7-10x higher than in ectotherms, so have higher food requirements.
533
Mammals have high aerobic metabolic scope:
5-10x higher than in ecotherms.
534
Mammals have high internal and constant temperatures:
28-42°C +/- 2°C.
535
Mammals exchange heat with the environment in different ways.
E.g., receiving solar radiation, radiating heat by thermal radiation and losing heat by evaporation etc.. The whole body may not be at the same temperature.
536
Winter Survival Mechanisms: Avoidance.
Body size, insulation, appendages, colouration, migration (marine mammals), microclimate modification (by communal nesting, or elaborate nests), food hoarding, reduction in activity, reduction in body mass and dormancy.
537
Bergmann's Rule (1847):
Larger species are found further north, and smaller species are found further south.
538
Mayr (1956):
Within species, larger ones are found in colder climates, further north, and smaller ones are found further south.
539
There's a positive correlation between hair length, and…
… its insulating value.
540
What is the coldest temperature Arctic fxes have been able to survive?
It's -70°C (it's critical temperature is -40°C)!
541
Blubber:
A matrix of fat and collagen for insulation in marine mammals.
542
Blubber thickness must be managed seasonally.
This creates seasonal variation in body mass. In some species, blubber may comprise up to 40% of their body mass in winter.
543
What stimulates seal sweat glands?
Waving their flippers. They may also pant, or reduce activity to cool down.
544
Appendage Adaptations:
Regional heterothermy, and countercurrent heat exchange.
545
Countercurrent Heat Exchange:
Arteries cool the blood as it passes away from the core, but in species in colder environments, the arterial blood gets cooler, and blood returning in the veins gets warmer because the blood vessels are closer together.
546
Regulation of Temperature in Caribou:
The core temperature is 36°C, but the limbs may only be 9°C as the meshwork of veins and arteries keep the temperature of the limbs near that of the environment, so that less heat is lost.
547
Allen's Rule (1877):
Mammals (and birds) living in cold climates have shorter and thicker appendages than close relatives in warmer environments.
548
Microclimate Modification:
Voles in the taiga dig deep nests to keep themselves separate from the surface conditions. Air temperature can decrease down to -20°C, and snow can become increasingly deeper, but the nest temperature below ground is much more constant than the external conditions.
549
Gloger's Rule (1833):
Species or subspecies or races in warm and humid areas are more heavily pigmented than those in cool, dry areas.
550
Seasonal Change in Colouration:
White winter coats in Arctic foxes.
551
Colouration and Differential Heating in Springboks:
Springboks orientate their long axis towards the sun, so their their pigmented backs absorb heat on one side, and release it on the other.
552
Euthermia:
Normal body temperature.
553
Winter Survival Mechanisms: Reduction in Activity and/or Basal Metabolic Rate.
Reduction in activity, e.g., shrews, reduction in body mass, dormancy, torpor and hibernation.
554
Reduction in Body Mass
Dehnel's Phenomenon. General overwinter mass decline, e.g., voles and shrews.
555
Dormancy: temporary abandonment of eutheria.
Reduced metabolic rate, and lowering of body temperature. Exhibited in 7 orders: marsupials, insectivores, elephant shrews, bats, primates and carnivores. Dormacy has evolved multiple times independently in mammals.
556
Torpor
A milder form of hibernation. Body temperature, heart rate and breathing rate are lowered. Tolerable body temperature range: 10-20°C. daily torpor can occur in response to an immediate energy emergency.
557
Hibernation:
Winter torpor. Profound dormancy. Body temperature remains at 2-5°C for weeks. In some species during hibernation, there's a bounce-back in body temperatute every week or fortnight.
558
Some Mammals with Particularly Low Basal Metabolic Rates:
Marsupials, especially koalas, tenrecs, sloths and echidnas.
559
Examples of Species That Hibernate:
hedgehogs, ground squirrels; marmots (the largest to undergo hibernation).
560
Adaptations to Heat: Avoidance.
Majority of activity is nocturnal, avoid exposure to high temperatures and burrows during the day, or finds patches of shades, e.g., Fennec digs burrows, or the heat shield created by the tail of the Cape groumd squirrel.
561
Kangaroo rates emerge from their burrws to feed for ~15 mins; then they must release this heat. How?
By concentrating this urine using an extra-large loop of Henle, and producing very dry faeces to reduce water loss. They recirculate the air in their nasal passages to re-capture the humidity, and condense the water from respiration.
562
How do antelopes keep a cool brain?
They circulate their arterial blood to release heat into tehir nasal passages to keep their brains cool.
563
The Oryx doesn't change its behaviour in response to heat.
E.g., it is still active in the day. It doesn't even sweat! However, it has physiological measures such as reduced basal metabolic rates and higher body temperatures. Whereas, the Eland seeks shade, and grazes at night.
564
Resistance:
Expending energy.
565
Avoidance:
Saving energy.
566
Winter Survival Mechanisms: Resistance.
Increase in thermogenic capacity by increasing basal metabolic rate, non-shivering thermogenesis and shivering. Energy is spent-- a debt that must be repaid.
567
How did early mammal ancestors become endothermic with a high basal metabolic rate and insulation?
Two hypotheses: Nocturnalisation and Aerobic Capacity.
568
Nocturnalisation (Crompton, 1978):
Ancestors became adapted to a nocturnal, insectivorous niche. This involves early mammals evolving an insulating layer, but there are no fossils to illustrate this. Moreover, insulation could have caused ectotherms to overheat, so a higher basal metabolic rate wouldn't evolve.
569
Aerobic Capacity (Bennet and Ruben, 1979):
Higher metabolism, but a greater food requirement. However, this heat would be lost without insulation. Therefore, it is likely that high metabolic rate and insulation evolved concurrently.
570
571
What is a mammal? Structure and Function: Feeding.
572
573
Maintaining a high body temperature requires regular acquisition of food.
Feeding relates to the high energy requirement of mammals, their variety of habitats and their adaptive radiation.
574
Lions often hunt large prey:
e.g., elephants several times tehir weight in Chobe National Park, and giraffes in northern Namia.
575
Some mammals have small prey.
Whales feed on plankton; many insectivores rely on termites.
576
Enamel wears away with age, so…
… more dentine is exposed.
577
How can we understand eth life-history traits, habitats and feeding strategies of extant mammals?
By examining their teeth.
578
The Pulp Cavity
Brings irrigation to the tissue.
579
Tooth Positions
Incisors, canines, premolars and molars.
580
Diastema
The gap between the canines and pre-molars. Not present in all species, but is obvious in ungulates.
581
Dental Formulae
E.g., 3/3, 1/1/, 3/3/, 3/3. Top/bottom. Incisors, canines, pre-molars; molars.
582
Position of the mandibular condyle differs between herbivores and carnivores.
The condyles in herbivores are higher up for sideways instead of vertical movement.
583
Primary Chewing Muscles Also Differ Between Herbivores and Carnivores:
The temporalis muscle in the back of the skull has a stronger role in carnivores, and the masseters in herbivores enable sideways motion.
584
Molars in Omnivores:
For crushing hard, brittle or turgid material.
585
Molars in Herbivores:
For grinding tough, fibrous material. Wear of the dentine gives different shapes that contribute to the grinding process.
586
Molars in Carnivores:
For shearing soft, or tough, material. Blades to cut through tissue.
587
Occlusal surfaces differ between different groups of herbivores:
Bunodont surface: typical of pigs. Lophodont dentition: typical of elephants with cusps in the form of transverse ridges. Selenodont: deer teeth with crescent-shaped ridges. Incisiform canines.
588
There is continuous growth of teeth in elephants:
A conveyor belt to cope with molar wear and tear.
589
Basal Form
Insectivore.
590
As mammals evolved in the Mesozoic, teeth became specialised to perform different functions:
Several trophic groups can be recognised: insectivores, omnivores, carnivores and herbivores. Specialised modes of feeding evolved from these four basic plans.
591
Plankton Specialists
Teeth adapted for filtration.
592
Squid and Fish Specialists
Teeth all of a similar size.
593
How many mammalian orders exploit the insectivorous niche?
9, from the echidna and platypus of the order Monotremata to the aardwolf that feeds solely on termites, belonging to the order Carnivora.
594
The Tamandua
A specialised, long; worm-like tongue anchored to the sternum that can be protruded extensively to catch ants and termites. Large salivary glands provide the sticky fluid to trap insects.
595
Insectivore Adaptations to Digestion
No cecum, and a short digestive system.
596
Carnivore Adaptations to Digestion
Short digestive system with a small cecum.
597
Non-Ruminant Herbivore Adaptations to Digestion
Longer intestine, larger cecum, but still a simple stomach.
598
Ruminant Herbivore Adaptations to Digestion
Multi-chambered stomachs, long small intestine, a large cecum and a long large intestine.
599
Convergent Evolution of Insectivores:
The numbat, aardvark and giant anteater are insectivores from very different evolutionary lineages.
600
Giant Anteater Skull
Lack of teeth, very thin lower jaw, and a very elongated nose to enable the siphoning of ants.
601
Aardvarks
Similar skull to giant anteaters, but they still have some teeth, albeit having lost specialisation.
602
Carnivory
Feeding primarily on animal material. Terrestrial, aerial, e.g., vampire bats, and aquatic carnivores, e.g., baleen whales are filter-feeders.
603
Teeth of Vampire Bats
Blade-like upper incisors to cut through their hosts' skin, and drink their blood.
604
Within the Canidae, muscles, condyles and teeth are adapted to differing food intakes:
Wounding bites (African wild dogs), puncturing grip (side-striped jackals) and rapid chomping (bat-eared foxes). This relates to ecological niches.
605
3 Broad Categories of Relationships Between Predator and Prey Mass:
Mob operators (Social animals attacking prey larger than themselves), the middle-way groupers (more generalists) and spatial groupers (smaller prey).
606
Why did the long sabre tooths evolve?
Unknown. Could be to pierce flesh, or hold prey. Found in marsupials, smilodons and other mammals by convergent evolution.
607
Herbivores:
Feed on green plants. Base of the consumer food web. Foregut and hindgut fermentation.
608
Foregut Fermentation:
Ruminants. Digastric digestive system.
609
Hindgut Fermentation:
Monogastric system.
610
Specialisations in Herbivory:
Granivory (grains and seeds), folivory (eats leaves, e.g., koalas), frugivory, nectarivory (e.g., honey possums), gummivory (gum-eating, e.g., bush-babies, marmosets and lorises) and mycophagy (fungus-eating, e.g., sciurids, cricetids; Potoridae).
611
The Tube-Lipped Nectar Bat
Muscles link up to the tongue, and extend to the sternum, allowing the tongue to be extended and retracted to eat nectar.
612
Gnawing Mammals
Have large incisors to reach the tenders parts of the plant, and to nibble grass and shrubs.
613
Coprophagy (Refection)
Eating its own faeces. By processing the low-quality, cellulose-rich food more than once, they get more out of it. Difestion of cellulose in hindgut fermenters occurs in the lsrge, microbe-containing cecum. Has evolved in shrews, lagomorphs and rodents to cope with the large amounts of vegetation.
614
Omnivory:
Opportunistic, they eat everything. Relatively simple digestion system, and versatile dentition, e.g., bunodont cheekteeth. E.g., primates, opossums, pigs, bears and racoons.
615
What are the foraging constraints for ruminants?
The need for sufficient sodium intake, the size of the rumen and the need to acquire enough food.
616
Aquatic Plants
Bulkier, but contain more sodium than aquatic plants.
617
Skull Telescoping in Modern Whales:
In modern whales, the bones have extended posteriorly to overlap with the parietal bones. Nostrils have moved, migrating backwards. The nasal bone has become the predominant bone. Many modern whales have lost their teeth instead of keratin baleens.
618
Prey size varies in baleen and toothed whales:
From giant squid and fish to zooplankton and tiny copepods.
619
The arrangement of baleen plates in the upper jaw of Mysticetes:
The size and number of plates varies between species.
620
Dentition Patterns in Pinnipeds:
Most marine mammals are generalist feeders with well-developed cheekteeth, usually single cusp and peg-like.
621
There is some specialisation in dentition in Pinnipeds:
Filter-feeding Crabeater seals have modified cusps, forming a sieve to filter krill.
622
Sirenians (Manatees and Dugongs):
Have reduced dentition: one incisor at the top, and some molars at the back-- 1/0, 0/0, 3/3, 3/3. The rostrum and lower jaw are deflected downward to facilitate bottom-feeding. Suction feeding strategy to eat algae and plants.
623
Why do Sirenians have dense, massive bones?
To increase body mass to overcome the buoyancy of shallow, saltwater habitats.
624
Pink Fairy Armadillos
Have large jaws, and swim through sand dunes. Very rare.
625
626
To Hunger or To Thirst
627
628
What % of absorbed water is used for plant growth and metabolism?
0.5%. The other 99.5% is lost in transpiration?
629
How much water does a maize plant transpire per day on average?
2-4L.
630
Stomata
A pore that opens when guard cells are turgid. Entry points for CO2, and exit points for water vapour.
631
Water flow from the leaf to the air:
Through veins, from veins to stomata and out of stomata.
632
What determines leaf conductance?
Xylem and out-of-xylem conductance.
633
What determines xylem conductance?
Xylem conduit length and diameter, xylem conduit abundance and pit structure and density.
634
What determines out-of-xylem conductance (from the vein to the stomata)?
Conductance of non-vascular cells, path length from the vein to the stomata and stomatal density and aperture.
635
Out-of-Xylem Conductance
Water leaves the xyelm vessel, then moves into the surrounding bundle sheath cells and enters the symplast. Water can then flow via the symplastic or apoplastic pathways to reach the stomatal cavity.
636
No chloroplasts in the bundle sheath cells of C3 plants, but…
… there are in C4 plants!
637
What determines how quickly water flows into the stomatal cavity?
Aquaporin activities: osmotic adjustments, cell wall thickness and distance to stomata. It is faster for water to flow the apoplast, so plants can regulate whether water pass through this pathway.
638
What forces water to enter the symplastic pathway (at least initially), after exiting the bundle sheath cells?
Bundle sheath cells have suberin, like the Casparian strip, to prevent entry of pathogens and salts into tissues.
639
Why are veins thin?
To minimise the distance from the xylem to the stomata, so the evaporation of water out of the leaf is more efficient, thereby cooling the leaf.
640
Why are mesophyll cells close to the xylem?
To keep them hydrated/prevent their desiccation. The same applies to guard cells as they need to be turgid to open the stomata.
641
Veins in Dicots
Reticulate veins with increasing vein densities.
642
Veins in Monocots
Parallel veins at two different densities.
643
Veins in Angiosperms Generally:
Short patwhay from the xylem to the stomata for efficient cooling and water movemnet. Steady supply of water and nutrients to photosynthetic cells and guard cells.
644
Veins in Gymnosperms:
Simple venation. More conservative. Less efficient in photosynthesis and transpiration. Lower conductance. Larger path from the xylem to the stomata than in angiosperms.
645
Pine Needles
An extreme case. A single veinw ith two strands of xylem and phloem.
646
What happens when water reaches the stomatal cavity?
Heat from the plant's tissues is used to vapourise the water, which diffuses out of the stomata, and is released into the atmosphere, if the pore is open. This cools the leaf.
647
What affects the diffusion of water vapour?
Number and aperture of stomata.
648
Different sizes of guard cell…
… give different sizes of stomatal pores.
649
Different species have different stomatal properties:
The Asiatic dayflower, that grows in high humidity, has high stomal density and large stomata openings. Succulents, that grow in semi-arid environments, have small stomata and low stomatal density.
650
Trade-off between…
… water transport capacity and safety.
651
Moist Environments
High stomata density, high carbon uptake, large pore size, large xylem conduits, more efficient photosynthesis, higher rates of transpiration, fast-growing, but vulnerable to drought stress.
652
Arid Environments
Lower stomata density, lower carbon uptake, less efficient photosynthesis, low rate of transpiration, smaller xylem conduits, slow-growing, but more resistant to dorught stress.
653
Hydraulic Failure
Irreversible xylem damage caused by an embolism.
654
When can and can't the plant recover from embolisms?
If only a few vessels are affected, the plant can recover. But if the drought is sustained, the stem can collapse, due to the pressure from the liquid-filled vessels surrounding the empty vessel that suffered from an embolism.
655
What exacerabtes tree mortality due to drought and hydraulic failure?
Pests, e.g., bark beetles, and opportunistic pathogens.
656
Why are perennials particularly vulnerable to pests and hydraulic failure?
Their longer lifecycles. Whereas for annuals, the next generation could be better adapted to cope with drought.
657
If the pores are open wide, …
… lots of CO2 can be obtained, but too much transpiration could be detrimental.
658
If the pore is almost close, …
… photosynthesis is inefficient, but water is conserved.
659
The Optimisation Point
For an environment, there is an optimum point to maximise carbon gain, and minimise associated costs (water loss and hydraulic failure).
660
Water Use Efficiency
A measure of how effectively a plant uses water to produce biomass. It is the amount of carbon assimilated or biomass/grain produced per unit of water used.
661
Water Use Efficiency varies between species.
E.g., CAM palnst are more water-use efficient than C3 plants.
662
How is Water Use Efficiency achieved for a particular species?
A complex interplay between stomatal regulation and allocation of resources.
663
How are stomata regulated?
By different signals, e.g., light, CO2 and water availability.
664
Light
Induces stomatal opening.
665
CO2
High CO2 promotes stomatal opening.
666
ABA
Produced in water scarcity to induce stomatal closing within minutes.
667
Temperature
Strongly increases transpiration rates in an upward-sloping curve that plateaus.
668
In higher temperatures, what happens to the amount of water vapour the atmosphere can hold?
It increases. Hence, colder climates tend to be drier.
669
Vapour Pressure Deficit
The difference between the maximum value of water vapour the atmosphere can hold, and the amount it actually holds.
670
Why is the risk of desiccation higher in hotter climates?
Vapour Pressure Deficit is greater.
671
What % of greenhouse gases does water vapour comprise?
50%. It absorbs infrared radiation emitted from Earth's surface, warming the atmosphere. It's contribution to global warming will increase with global temperatures.
672
Only a fraction of the sun's energy is used for carbon assimilation:
PAR: Photosynthetically Active Radiation, 400-700 nm. 60% of wavelengths are not absorbed. Only about 5% ends up being used.
673
What % of solar energy is reflected (and transmitted) by plants?
8%.
674
What % of solar energy si dissipated as heat by plants?
8%.
675
What % of solar energy is lost in metabolism?
19%, e.g., in photorespiration, respiration and in maintenance/repair.
676
How do plants dissipate heat?
As infrared radiation (long-wavelength radiation from the surface), it can be lost to the air (sensible heat loss: conduction and convection to cool the air) and latent heat loss (evaporative cooling from water loss, up to 15°C below ambient temperature).
677
Leaf Radiation Balance
The equilibrium between incoming and outgoing radiation that determines the leaf's temperature, and thus, also transpiration, photosynthesis and overal plant function, e.g., by denaturing proteins.
678
Stomata in Hornworts
Found in the gametophyte and sporophyte.
679
Stomata in Moss and Tracheophytes
Found only in the sporophyte.
680
Evolution of stomata and their regulation was a fundamental step in land plant evolution.
Stomata and their regulation by ABA occurred early on in land plant evolution, e.g., fossils of Silurian stomata 420 mya.
681
The Earliest Vascular Plant
Cooksonia. In the late Silurian/Early Devonian. 430 mya. Small.
682
Rhynia
Early Devonian. Wood fossil. 410 mya. 15-20 cm. A vascular plant.
683
Archaeopteris, Cordaites and Lepidodendron.
Wood fossils from the late Devonian. 380 mya. Trees up to 35m tall! Wood allows for more efficient water transport with its rigidity.
684
What caused the massive decline in CO2 concentration in the late Devonian?
CO2 was absorbed directly via stomata, roots wore away the silicate rock, thereby releasing minerals that reacted with CO2 to form insoluble carbonates, e.g., CaMgCO3, and when these plants dies, much of this carbon was buried as coal, instead of returned to the atmosphere.
685
Drop in CO2 created a pressure for plants to evolve leaves to obtain more CO2.
Evolution of stems into microphylls, then into megaphylls increased light absorption and photosynthesis, decreasing CO2 further. This also increased stomatal density.
686
What does stomatal density mean?
Enhnaced transpiration, photosynthesis and cooling capacity.
687
Life-History Strategies for Survival in Arid Environments:
Drought-escape by leaf-deciduosness and dormancy, or seeds and a short lifecycle.
688
Seeds and a short Lifecycle:
E.g., ephemereals in Namaqualand, mostly belonging to the Asteraceae family. Upon rainfall, there is a very fast germination of seeds from the previous season. Quick reproduction ensures a new seed bank before the drought returns. They then complete their lifecycles quickly, and survive as seeds in the drought. They don't actually face the drought.
689
Drought-Deciduous Strategy
Leaf abscission: plants shed tehir leaves during drought, then are dormant as buds. Some of these leaves produce buds up to six times per year, requiring fertile soils. Before the leaves are shed, there's a remobilisation and collection of nutrients in the leaves. E.g., Fouquieria splendens (ocotillo) in U.S. deserts.
690
Morphological Adaptations to Drought
Cavitation-resistant xylem, small leaves, leaf surface characteristics, dimorphic roots, extensive deep root systems and variation in the size and number of stomata.
691
Phreatophytes
E.g., Shepherd's tree, ensure a constant water supply by growing very deep roots into the groundwater.
692
Dimorphic Roots
E.g., Opuntia.
693
Another Type of Dimorphic Roots:
E.g., Acorn banksia. A sinker/tap root grows into the groundwater (up to 15m deep!) to ensure a constant supply of water throughout the year, then the lateral roots absorb the water from hydraulic lift by the sink root. Cluster roots form in response to rain.
694
Cluster roots are ephemeral:
They facilitate the uptake of key nutrients by secreting organic acids, e.g., malate, oxalic acid, to solubilise the rock to extract nutrients,e g., phosphates.
695
Where is the Acorn banksia grown?
Nutrient-poor, sandy places such as the Sandplains of the Southwest Province of Western Australia.
696
Smaller Leaves
Less transpiration, but the higher surface area: volume ratio means more efficient sensible heat exchange with the air, cooling the leaves. E.g., Acacia in Madagascar, Ocotillo.
697
Heterophylly in Encelia farinosa:
Large, green winter leaves in the cool, moist season with low pubescence and high photosynthetic capacity by absorbing lots of light. Later in the summer, it produces small leaves with a much higher density of fine, reflective hairs. These reflect more sunlight, and keep the leaf temperature lower, and reduce water loss. Absorbance decreases from 0.8 to 0.3. If the drought intensitifies, drought-deciduosness occurs.
698
Hairs allow animals to maintain a cooler temperature on the head.
The Saharan silver ant has hairs on its head. It forages at 70°C, but its optimal body temperature is 48-51°C.
699
In the submerged roots of Mangroves:
High accumulation of solutes in root cells to enable water intake. Very efficient Na+ exclusion, e.g., there are aerial roots for respiration. Their water channels also exclude salt.
700
Salt Secretion and Abscission in Mangroves:
Salt glands expel salt. Salt accumulates in older leaves, which then undergo senescence and abscission.
701
Viviparous Seeds in Mangroves:
Seeds germinate on the tree to minimise salt exposure durinhs ensitive development. They only drop once they have established adaptations to survive in the environment.
702
Epiphytes
Collect water in a water tank, and/or have folair water uptake via specialised hairs-- trichomes. The dead cells in the trichomes form pipes/cavities to absorb water. They often also have a thick cuticle, CAM photosynthesis, aerial roots and pseudobulbs.
703
Epiphytic orchids have a velamen radicum.
A spongy layer of dead, specialised cells in the epidermis of the roots that absorb moisture and nutreints efficiently, and pass it to the inner layers.
704
Where is the cushion/rosette habitat found?
In Arctic and alpine environments. Examples include: Azorella compacta and Lobelia telekii.
705
The Cushion/Rosette Habit:
Boundary layer insulation: reduces wind exposure by creating a boundary layer of still air, insulating the plant from extreme temperatures. Heat retention: maximises energy input by irradiated during the day. Nyctinastic leaf movements maintain central meristematic meristem tissue above ambient temperature during the night, preventing the freezing of cellular water.
706
707
Plant Energy Balance and Ecological Diversity
708
709
Internal CO2
Can affect stomatal closure. Not just atmospheric CO2.
710
Why is it called C3 photosynthesis?
2 x C3 3-phosphoglycerate is the first product of carbon assimilation.
711
Calvin's Lollipop: Pulse Feeding with 14C.
C14 in hydrogen carbinate was fed into Chlorella algae. They then traced into which compounds the isoptope was incorporated. At specific time intercals, they aliquoted the algae into ethanol to stop the reaction. Those aliquots were then analysed with chromatgraphy to detect where the radioactivity was incorporated.
712
What did Calvin's lollipop detect?
The first products were 2x 3-phosphoglycerate. 30s later, TCA cycle intermediates and amino acids were detected.
713
Why were Calvin and colleagues initially confused?
They never detected a 2C molecule to which CO2 could be joined.
714
Calvin-Benson Cycle Summary:
Carboxylation: 3 CO2 are added. Phosphorylation: uses 6 ATP. Reduction: uses NADPH. 1 GAP is used for biomass production. 5 GAP are used for regenerating RuBP.
715
There is a fine balance between ATP and NADPH production in the light-dependent reactions, and…
… their consumption in the Calvin-Benson cycle. Thus, ATP and NADPH must regenerated. This balance is endangered by stresses, e.g., water stresses.
716
Rubisco
A large, multi-subunit enzyme, L8S8, requiring heavy investment in protein nitrogen. The plant requires lots of C and N to build this.
717
Rubisco has a very low catalytic rate:
It has a low turnover number (~3 s^-1). Hence, lots must be produced to compensate. Rubsico comprises ~50% of the soluble protein in tissues. It's the most abundant protein on Earth.
718
Rubsico Has a Low Affinity/High Km for CO2:
Only 50% are CO2-saturated in C3 plants under present-day conditions. It has relatively poor selectivity for CO2 over O2 under typical physiological conditions.
719
Rubisco can catalyse the carboxylation reaction with CO2, but it can also…
… react with O2 in an oxygenation reaction.
720
What is produced instead of one of the 3-phosphoglycerates in photorespiration?
2-Phosphoglycolate, which is less efficinet. 2-phosphoglycolate is also toxic, so must be recycled. It is recycled through chloroplasts, mitochondria and peroxisomes. This recycling process leads to the loss of CO2.
721
Rubsico has 100x higher affinity for CO2 than O2, but…
… O2 is 500x more abundant in the atmosphere, so the higher affinity for CO2 is hugely outweighed.
722
Photorespiration has some benefits under certain conditions:
E.g., nitrogen assimilation, protection from excessive light damage. It also helps to avoid the production and consumption of NADPH and ATP. However, under optimal conditions, photorespiration is mostly detrimental.
723
As temperature increases, the proportion of rubisco's activity dedicated to photorespiration over photosyntheiss increases. There is a two-fold explanation why:
The oxygenase activity of rubisco increases over the carboxylase activity. The concentration of dissolved CO2 in solution declines more than that of O2.
724
Even under optimal conditions, what is the % of CO2 lost through photorespiration?
20-25%.
725
Adaptations to cope with photorespiration:
C4 and CAM. They both increase the local concentration of CO2 around rubisco, but in different ways.
726
How was C4 discovered?
14CO2 pulse-chase labelling studies in sugar cane revealed a new carboxylation reaction. The first product wasn't 3-phosphoglycerate, but malate and other C4 acids.
727
C3 + CO2 --> C4
The initial carboxylation is done by phosphoenolpyruvate carboxylase (PEPC), not rubsico.
728
Most C4 plants have Kranz anatomy, revealing specialised functions:
The bundle sheath cells are larger, and filled with chloroplasts, then are surrounded by mesophyll cells. There is a much higher ratio of bundle sheath cells to mesophyll cells in C4 than C3 plants.
729
In C3 plants, rubisco is only found in the mesophyll cells.
In C4 plants, it's also in the bundle sheath cells.
730
C4 photosynthesis spatially separates carbon assimilation and fixation.
CO2 enters the mesophyll cells, and is converted to bicarbonate by carbonic anhydrase. PEPC uses this to carboxylate phosphoenolpyruvtae to form oxaloacetate. This C4 acid, or a derivative, diffuses across the plasmodesmata into a bundle sheath cell, where it is decarboxylated to release CO2. Rubisco uses this in the 2nd carboxylation, initiating the Calvin-Benson cycle. 3-phosphoglycerate diffuses back into mesophyll cells, where it used in regeneration of RuBP and making biomass.
731
Difference in CO2 concentration between the mesophyll cells and bundle sheath cells in C4 plants:
150 ppm in mesophyll cells. 2000 ppm bundle sheath cells. This maximsies the carboxylation reaction, and supresses the oxygenase activity of rubisco, almost elimiating photorespiration.
732
Why is there such a high CO2 gradient in C4 plants?
Phosphoenolpyruvate carboxylase (PEPC) has a higher affinity for CO2 (as bicarbonate) than rubisco does. PEPC is also more efficient, so the CO2 concentration in mesophyll cells is lower than in the bundle sheath cells because it's always being used up. thsi means teh CO2 gradient is greater, thereby enhancing the gradient of CO2 from outside the plant.
733
What makes C4 particularly advantageous in dry regions?
Even with half-open stomata, diffusion rate is double, so carbon can be gained as efficiently with half the loss of C3 plantsC4 plants have two-fold higher water use efficiency.
734
Why is C4 advantageous in heat?
Photorespiration increases with temperature, and C4 does less photorespiration.
735
Why is C4 advantageous in sunny regions?
Unlike C3 plants, carbon-fixation in C4 plants is not carbon-limited, so they are able to take advantage of the increased ATP and NADPH produced in higher light intensities. C4 photosynthesis is not saturated, even in full sunlight.
736
Natural C4 Biomes
Tropical savanna, and saline habitats.
737
Maize/Corn
The most economically important C4 plant, and the 4th-most economically important crop plant.
738
What is the second-most important C4 plant economically, and the sixth-most economically important crop plant overall?
Sugar cane.
739
Other Economically Important C4 Species:
Tef, pearl millet, foxtail millet and sorghum.
740
Total Number of C4 Species
8000. Present in >65 lineages. 2-3% of all angiosperm species.
741
Major Families of C4 Plants
Mostly grasses and sedges because these plants already had an anatomy pre-disposed to developing C4. E.g., larger bundle sheath cells. These also grow in habitats where C4 is advantageous.
742
Global Distribution of C4 Plants
Predominantly in tropical savannas and subtropical grasslands.
743
What ~% of terrestrial productivity do C4 plants contribute?
20-25%.
744
Two Main Ecological Groups of C4 Plants:
1. Tropical and subtropical grasses and sedges. 2. Highly stress-tolerant plants, e.g., haplophytic eudicots.
745
C4 has evolved mote than 60 times, mostly in hot, dry regions. What are the drivers for this?
Heat, drought, salinity and low atmospheric CO2. C4 photosynthesis increases biomass production in warm, dry and sunny regions. This strong advantage has beens elected for repeatedly.
746
All the enzymes required for C4 photosynthesis are present in C3 plants:
E.g., carbonic anhydrases, PEPC and decarboxylases. It has been relatively easy for plants to acquire the capability for C4 photosynthesis from the C3 ancestral state. It could be feasible to engineer features of C4 photosynthesis in C3 crop plants such as rice and soybean.
747
What is required to evolve C4 from C3?
Often gene duplication. Changes in gene expression patterns. Changes in subcellular localisation. i.e., expressing genes in different cells, and the anatomy for physical separation.
748
The transition to C4 can be studied in C4-inducible plants:
Eleocharis vivipara, an aquatic sedge, is a facultative C4 plant. Underwater, it does C3 photosynthesis, but when exposed to air or due to ABA signalling, it can change to C4 as this is more productive.
749
How was Crassulacean Acid Metabolism (CAM) discovered?
De Saussure (1804): cacti simultaneously take up CO2 and O2 at night. 1815: nocturanl acidification of tissues. Inverse rhythym of stimatal opening, i.e., open at night. Carbohydrate levels are inversely correlated with organic acids. Bonner and Bonner (1949), and Thomas and Beevers (1949) elucidated the reactions taking place.
750
How does CAM work?
1. CO2 uptake at night as stomata are open at night to reduce water loss. 2. CO2 --> HCO3^-1 by carbonic anhydrase. 3. HCO3^-1 is fixed by PEPC into an organic acid, e.g., malic acid. 4. C4 acids ae stored in the vacuole. 5. Daytime decarboxylation releases CO2 for use by rubisco.
751
What's the difference between C4 and CAM palnst when they both use a C4 intermediate?
In C4 plants, PEPC and rubisco are spatially separated into the bundle sheath cells and mesophyll cells. In CAM plants, the carboxylases are temporally separated as the PEPC is only accessible at night, but the CO2 is only available during the day.
752
Both pathways minimise photorespiration and conserve water, but…
… CAM is generally superior in water conservation, particularly in very dry environments, because the stomata in CAM plants are all the way closed, not half-open.
753
Economically Important CAM Plants:
Many orchids, including the vanilla orchid, aloe vera (used medicinally for centuries), many brmeliads, including pineapple, and agave plants (including Agave tequiliana, some grown as bioenergy crops and some grown for fibres (sisal)).
754
CAM is much more widespread than C4:
It's found in 37 families; there are 15-17,000 species.
755
What % of angisoperms are CAM plants?
5-7%, but they account for only 10% of the terrestrial NPP. They dominate in certain niches, e.g., deserts, as CAM plants are mainly xerophytes and epiphytes.
756
Many plants are facultative CAM, so use CAM when stressed.
Drought induced a switch to night-time gas exchange. As water is withheld, facultative Cam plants displayed decreased CO2 consumption in the day, then increased CO2 consumption at night. When water was returned, the pattern of high CO2 consumption in the day also returned. This is corroborated by tissue acidification.
757
Physiological Properties of CAM Plants:
3-6 times more water-use efficient than C3 plants, and at least as efficient as C4 plants, high tolerance of environmental stresses (e.g., drought, salinity, high irradiance; nutrient-poor soils), but maximum photosynthetic rates and growth rates are generally lower than C3 and C4. CAM is an adaptation for survival, not productivity.
758
3 Main Ecological Groups:
1. Desert and semi-desert regions (e.g., cacti, agave). 2. Rock outcrops, and high-altitude environments. 3. Tropical and sub-tropical forests (particularly as epiphytes, such as bromeliads and orchids).
759
When did C4 evolve?
When CO2 levels started to decline 65 mya.
760
When did CAM evolve?
5-20 mya.
761
What is expected to happen with regard to C3 vs. C4 vs. CAM plants under the conditions of current rising CO2 levels?
C3 plants are expected to benefit more from elevated CO2 levels compared to C4 and CAM plants. For C4 plants, no benefit is gained, if CO2 increases past a certain point, but for a C3 plant, this still makes a huge difference. Elevated CO2 levels increase water use efficiency.
762
Ambient CO2 Levels Today
>440 ppm.
763
764
Vascular Plants and Life on Land
765
766
Stomatal Conflict
There's a conflict between opening stomata for CO2, but plants also need to avoid water loss.
767
Why should it be referred to as the conquest of the highly-desiccating atmosphere instead of conquest of land (by plants)?
This is the greatest challenge for embryophytes.
768
Homiohydry:
Most vascular plants. The ability of plants to mainatin a cosntant internal water content by regulation. Their sensitivity to desiccation varies, but they are all desiccation-sensitive. Includes mesophytes and xerophytes.
769
Poikilohydry:
The ancestral strategy. The inability of plants to internally regulate their water content. Desiccation-tolerant, e.g., they accumulate protective compounds, so their tissues remain viable. Found in most bryophytes, and a few vascular plants, where it re-evolved.
770
What two climate axes help delineate the major terrestrail biomes?
Mean annual precipitation (mm), and mean annual temperature(°C). Earth's natural vegetation varies dependent on water availability and temperature.
771
Savanna
Transition biome between the forest and grassland.
772
How does annual Net Primary Productivity (NPP) vary with precipitation in different biomes?
In drier climates, annual NPP is almost a linear function of precipitation. However, in places with high rainfall, then other factors become limiting, e.g., light availability.
773
Water Potential, Ψw:
The sum of the osmotic potential (Ψπ), pressure potential (Ψp), the gravitational potential (Ψg) and others (e.g., matrix potential, which depends on the soil properties, Ψm).
774
Water moves through a soil-plant-atmosphere continuum. Why is it a continuum?
Water is cohesive, due to it being polar, so it can form columns of liquid.
775
3 Steps in Water Flow through the Soil-Plant-Atmosphere continuum:
1. Water uptake into the roots-- short-distance movement of water. 2. Long-distance transport in the xylem. 3. Short-distance transport through the leaf and into the air by evaporation. All rely on the principle that water moves from a high water potential.
776
Pure Water:
0 Mpa.
777
Apoplastic Pathway:
Water goes through cell walls as the cell walls of adjacent cells are connected. The cell wall is hydrophilic and highly porous. The speed is determined by diffusion. No crossing of the plasma membrane.
778
Symplastic Pathway:
Diffusion inside plant cells. Crosses the plasma membrane once, into the cell, then diffuses through the plasmodesmata.
779
Transcellular Pathway:
Crossing multiple plasma membranes.
780
Only in very tall trees, does…
… gravity play a role in water movement.
781
Short-distance water movement is just diffusion:
Water particles move down the water potential gradient towards the equilibrium.
782
In the symplastic and transcellular pathways:
The semi-permeable cell membrane (largely permeable to water, but not solutes) must be crossed by osmosis.
783
What enhances the passage of water across the plasma membrane?
Aquaporins: selective pores/water cahnnels that increase the permeability of the cell membrane to water. They can open, and close.
784
Osmotic Potential in Freshwater
~ 0 Mpa.
785
Osmotic Potential for a Typical Cell:
Approximately -0.8 Mpa.
786
Osmotic Potential for Seawater:
Approximately -2.5 Mpa.
787
Osmotic adjustments allow palnst to prevent water loss.
When plants are in high salinity, drought or frozen soil, the water potential of the cell is lowered, so water exits the plant. To prevent this, plants accumulate compatible solutes, e.g., sugars (e.g., trehalose, fructans, sucrose; raffinose), sugar alcohols (e.g., mannitol, sorbitol) and amino acids.
788
Fructans
Complex sugars, omoprotectants and probiotics. Accumulated by onions, Agave, wheat and chicori.
789
When did Fructan-accumulating taxa evolve?
30-15 mya, when seasonal droughts became more frequent.
790
Currently, Fructan-accumulating species are:
Almost absent in tropical regions, but are found in regions of seasonal drought.
791
Water diffuses into the root, then reaches the endodermis. What happens there?
It encounters the Casparian strip: this blocks apoplastic water flow, as all the cell walls of eth endodermis are impermeable through impregnation with lignin and suberin. This forces water to cross the cell membrane through aquaporins. This enables selectivity for water and nutrients (via transporters).
792
The plant's essential requirements: above-ground.
Sunlight and CO2.
793
The plant's essential requirements: below-ground.
Water macronutrients (N, P, K, S, Mg and Ca), and micronutrients (Si, Cl, Fe, B, Mn, Zn, Cu, Ni and Mo).
794
The concentration of different nutreints varies massively:
E.g., NA is required at high concentrations, as it's involved in maintaining membranes, whereas Molybdenum is needed in low concentration, because it's just needed as a co-factor for some enzymes. All the nutreinst are still needed though, so if they are not there, they are limiting. They all have transporters.
795
Soil properties affect the movement of water:
E.g., clay lacks O2, and is porous. It's formed of very small particles with high surface area : volume ratio, so water tends to stick to thes eparticles more strongly than in sand or silt.
796
The smaller the particle size, …
… the lower the matrix potential, so the lower the water potential.
797
Properties of the Root Affect Water Absorption:
E.g., fibrous roots systems, such as in grasses, vs. tap root systems.
798
Tap Root Systems:
Main vertical growth with lateral roots coming off it.
799
Other Factors Affecting Absorption by the Roots:
Angle of the roots, length of the roots, number of root hairs that increase the surafce area for water absorption; branching and density of lateral roots.
800
Root length varies hugely in different terrestrial biomes:
Shepherd's tree in the savanna has 68m-long roots to reach the groundwater all year round. Whereas in cropland an the boreal forest, the length of roots is ~4m.
801
Root length varies between different trees in the same biome:
In the seaonal amazonian forest, understory trees have <1m-long roots. Canopy trees have roots up to 8m-long to fulfill the high water demand (due to size), even in the dry season.
802
Root Systems in Cacti:
Roots only in the superficial layer, 1.5m-deep, but then they spread laterally 2-3m. Amny form de novo roots just after rain.
803
Ephemeral Roots Produced By Cacti After Rain:
These roots have characteristics for better water absorption and trasnport-- greater conductance. The water is stored. Once the soil dries, these roots are shed to minimise water loss.
804
Transport in the Xylem:
Evaporation of water generates a suction/negative pressure in the xylem that lowers the water potential, thereby driving the water upwards.
805
In short-distance transport, the time it takes for a molecule to diffuse is proportional to the distance it diffuses, according to Fick's law.
Time = Distance^2/4D, where D is the diffusion coefficient of the molecule (typically, 10^-9 m^2 s^-1).
806
Why can't diffusion account for long-distance transport of water?
Diffusion of water across a 50µm cell takes 0.6s, but diffusion across 1m would take 8 years.
807
Hydraulic Lift-Redistribution:
During the night, there's no transpiration, so dry soil draws water from lateral roots. This generates a suction in the xylem that draws water from the main deeper root. Water is now in the upper layers, so can be used by the lateral roots to absorb nutrients, and by other species. This is ideal for absorbing nutrients present in the upper layers, but not in the lower layers.
808
Maple Trees:
Have dimorphic roots:a tap root and lateral roots. They create hydraulic lift.
809
Shallow-Rooted Species, Such As Meadow Rue, and Wild Strawberries:
Can derive a significant portion of their water (up to 60%) from the water lifted by sugar maples during periods of drought.
810
Cells that become xylem:
Elongate, deposit lignin-rich cell walls that make them water-impermeable, so water cannot enter nearby cells, then cells undergo apoptosis to leave a hollow tube. Lignin minimises leakage of water as well as providing extra structural rigidity.
811
Evolutionary Origins of Wood:
Evidence of secondary xylem from the early Devonian ~400 mya.
812
Why wouldn't have wood evolved for structural support initially?
Early Devonian plants were small (<1m) with small cells, so wood would have evolved for water transport.
813
When did wood become more important for increasing height?
As CO2 levels decreased with the proliferation of plants, more stomata and more complex leaves evolved, so the structural aspect of wood became more important for increasing height.
814
Bulk flow through a tube is affected by the diameter of the tube.
Wider conduits have higher conductance (capacity to transport water), but the relationship between diameter and the flow of water is not linear. Flow increases with radius to the fourth power.
815
The xylem has two elements:
Tracheids, and vessel elements-- two different types of vessels.
816
Tracheids:
Found in gymnosperms and angiosperms. Closed end walls. Narrow (5-80 µm), so have low water conductance. Thick cell walls, so provide structural support in addition to transport. Short: 0.1-1cm. Perforated on the sides by complex pit membranes.
817
Vessel Elements:
Only in angiosperms. Wider diameters: 15-500µm, so have higher water conductance. Thin cell walls, so predominantly for transport. Length: 1cm-1m, as they can assemble into tubes/pipes. Perforated by simple pit membranes on the sides. Open (or perforated) end walls, so can form a tube.
818
Larger elements can transport more water, but…
… there is a greater probability of trapping an air bubble (an embolism/cavitation), because the larger column of water is more likely to break under high pressure.
819
What causes cavitations?
In drought, the rate of evaporation is exceeded by the rate of absorbance through the root, so the suction in the xlyem can break, and air can be generated inside the vessel. More likely in wider vessels, but can still occur in the tracheids.
820
Pits:
Parts of the cell wall that are just cellulose --not lignin-- that allow water to pass between vessels, but not air. Though this means less water can pass, it's safer for the passage of air. Pits act as safety valves.
821
No embolism:
Water on boths ides of the pit membrane.
822
Some pits are more embolism-resistant than others:
Embolism-resistant pits block embolism movement between conduits. Pits with a large torus can seal the pit membrane. Many desert plants have vestured pits with wall elaborations. Thick pit membranes can resitant embolism movement. The pit memebrane is pulled due to the tension/pressure difference between the two sides.
823
Conifers:
Have narrower tubes than lianas, so can transport less water.
824
Trade-off between the ability to tarsnport more water, and the risk it represents, i.e., the risk of acvitation in drought:
Large xylem diameter maximises conductance, whereas a small diameter minimises embolism risk, and maximises strength.
825
What is required to drive water up taller trees?
A greater negative pressure must eb exerted to overcome gravity. The taller the tree grows, the more gravity counteracts the flow of water.
826
Higher up in the tree, …
… it's easier to break the column, so the tree invest less in the leaves for photosynthesis: they are smaller with thinner vessels to reduce risk of embolisms. There's a trade-off between the ability to photosynthesise, and the aility to transport water with a lower risk of embolisms.
