Week 9: Species, Speciation and Extinction

Question 1

How many species are there?

Answer 1

2 million species described - estimate 5-10 million

Question 2

Describe mosquito speciation in underground London

Answer 2

Culex pipiens - above and underground - morphologically similar but behaviourally different in feeding and breeding patterns - no gene flow in nature - in lab - hybrid cross produced no viable offspring.

Question 3

What is the species problem?

Answer 3

1) how to define a species 2) how to identify species in nature and delineate boundaries between them?

Question 4

What are the 5 main species concepts?

Answer 4

evolutionary, phenetic, biological, ecological, phylogenetic.

Question 5

Describe evolutionary species concept

Answer 5

a lineage of populations which maintains its identity from other lineages and which has its own evolutionary tendencies and historical fate.

Question 6

Describe phenetic species concept

Answer 6

delineates species based on phenotypic similarity. Pros - can be used on extinct species (using fossils), can use genetic data in similar way. Cons - doesnt include evolutionary history (traits could be same due to convergent evo and not due to shared evolutionary history), fails when within-species variation is high or between-species variation is low.

Question 7

Describe biological species concept

Answer 7

delineates species based on reproductive isolation. Species are groups of actually or potentially interbreeding populations which are reproductively isolated from other such groups. If two individuals breed and produce fertile offspring - they are same species. identifies mechanism of speciation to be patterns of gene flow. Cons - extinct species, asexual species, hybridization events.

Question 8

Describe ecological species concept

Answer 8

delineates species based on niche. Individuals of same species compete most closely with each other. Evolution is underlying mechanism (need to get away from competitor - evolve new niche). Pro - can be used for asexual species - possibly for extinct species. Con - doesnt work well on species with different morphs.

Question 9

Describe phylogenetic species concept

Answer 9

based on shared evolutionary history - members of species share common evo history and common fate - distinct from other species. The smallest monophyletic group distinguished by a shared derived character. Puts a scale on species delineation - all mammals have fur and mammary glands but mammals are not all same species. Cannot use polymorphic traits - wont form a clade (ie. flower colour), can use shared derived traits (by definition). Concept may delineate too finely based on shared derived traits.

Question 10

Describe Cattail case study

Answer 10

Broad-leaf (Native), Narrow-leaf (non-native), hybrid cattail (hybrid).

Biological SC - F1 hybrids readily formed, hybrids are fertile but it is reduced compared to parents. Once formed, hybrid has greater clonal growth than parents

Phenetic SC - They do delineate based on morphology of leaf width - also height, gap, spike width and spike length.

Ecological SC - share niche based on water depth

Phylogenetic SC - T. latifolia is monophyletic, T. angustifolia is paraphyletic or polyphyletic

Question 11

Why do species concepts matter?

Answer 11

Why species concepts matter - use taxonomy to make conservation decisions, one of first criteria for COSEWIC is “is it taxonomically valid”, for eastern wolves, it is a public opinion, currently Canis Lycaon cf. - cf means things are complicated

Question 12

What are modes of speciation based on?

Answer 12

Biological species concept - reproductive isolation; caused by genetic divergence

Question 13

What are the 3 modes of speciation?

Answer 13

1. Allopatric - speciation in different places - geographically isolated
2. Parapatric - speciation in populations adjacent to each other
3. Sympatric - speciation in same place.

Question 14

What is the vicariance model of allopatric speciation?

Answer 14

one very large pop subdivided into two large populations. Drift unlikely due to large size of subpopulations - different selective pressures.

Question 15

What is the peripheral isolate model of allopatric speciation?

Answer 15

division of populations that are diff sizes - one large and 1+ small. Founder effects and drift occur in small subpops - still different selective pressures.

Question 16

What is an example of allopatric speciation?

Answer 16

Example: Vicariance in Alpheus shrimp - Isthmus of panama creates physical barrier between seas. Species from opposite sides formed sister species. Mating yielded 1% viable offspring between sister species vs. 60% within sister species.

Question 17

What is parapatric speciation?

Answer 17

Speciation in absence of geographic barrier. Diverging populations form a cline - spatial gradient the frequency of phenotypes or genotypes. Different selective pressures along the cline. Gene flow between diverging populations results in hybrid zone. Hybrids usually selected against - not well suited to live anywhere on cline.

Question 18

What is an example of parapatric speciation?

Answer 18

hybrid zone in sweet vernal grass - grows on mine - soil contaminated with lead and zinc - grows on adjacent pasture where soil is not contaminated. Some gene flow between pasture and mine - interpopulation hybrids - not much. Pasture plants outcross more, flower earlier. Mine plants highly selfing. Differences in reproductive traits greatest closest to pasture-mine boundary.

Question 19

What is a ring species?

Answer 19

populations connected in a circle/ring. Evolved directionally such that those at the ends have no direct gene flow. ie. salamanders in Cali

Question 20

What is sympatric speciation? What drives it?

Answer 20

Divergence with geographic overlap - no geographic boundary. ie. cichlids in Nicaragua’s Lake Apoyo. Hypothesis that arrow cichlid evolved from ancestral population of Midas - supported by phylogeographic, genetic, ecological and morphological evidence.

Resource competition model - competition drives it.

Question 21

What happens when incipient species comes back into contact? How does it reinforce reproductive isolation?

Answer 21

Reinforcement and secondary contact.

Secondary contact and low hybrid fitness reinforces reproductive isolation.

Question 22

What is reproductive character displacement?

Answer 22

when reproductive traits are most dissimilar between species in areas of overlap (sympatry). If hybrids at a disadvantage, ability to mate with other species should be most strongly selected against where hybrids most likely to form ex. reproductive character displacement in snails.

Question 23

What are reproductive isolating mechanisms?

Answer 23

prezygotic (before fertilization - deter or prevent mating, prevents fertilization, mechanical, temporal, behaviour, habitat). Postzygotic (after fertilization - deter or prevent viable offspring from being born, lack of hybrid variability, infertile offspring).

Example: isolation through pollinators - many plant-pollinator relationships are obligate - one pollinator for one plant. Reproductive isolation between plant species due to specialist pollinators. Different flower shapes, pollinators, limit gene flow between species.

Question 24

What are the genetics of reproductive isolation?

Answer 24

• Isolation through changes in chromosome number (ploidy)
• Isolation via Dobzhansky-Muller incompatibility
• Isolation through Haldane’s rule
• Ploidy - error in meiosis yield unreduced gametes. Species with different ploidy levels can often interbreed but hybrids are sterile. Common in plants - self-fertilization while waiting for viable mates - increased ploidy = larger cells, larger seed sets and larger pollen grains.
• Dobzhansky-Muller Incompatibility - Reproductive isolation is result of negative interactions between alleles that arose in diff genetic backgrounds - hybrids selected against because alleles from parent - postzygotic - species (or pops) incompatible - maintains reproductive isolation between parent species (or pops).
• Haldane’s Rule - Among hybrid offspring - if one sex is rare or sterile it is the heterogametic sex. The heterogametic sex is at a fitness disadvantage - creating a bias for reproductive isolation
  Copious evidence supports idea
  Example: almost all surviving hybrid howler monkeys are female (homogametic sex).

Question 25

What is Scala Naturae?

Answer 25

Historically extinction what thought to be impossible - Scala Naturae - Great Chain of Being - extinction not accepted in 1700s

Question 26

What were the first fossils assumed to be?

Answer 26

Humans found fossilized teeth from L’animal de l’Ohio and American Mastodon - believed their were from animals that were still alive.

Question 27

What did George Cuvier do?

Answer 27

demonstrated that African and Indian elephants were distinct species. Fossilized bones from mastodons were from a distinct species that no longer existed. 1790’s - proved animals could go extinct (expert in skeletal anatomy - conducted detailed comparisons of fossil animals with extant ones)

Question 28

What is the concept of extinction?

Answer 28

species becomes extinct when all individuals have died out and left no living descendants. When extinctions occur - phylogenetic diversity lost can vary. Ex. tuatara lizard shares similar features to iguanas but represents a very deep node of only two species - loss would be significant phylogenetic diversity loss.

Question 29

What does the fossil record give?

Answer 29

History of life on Earth

Question 30

How are fossils dated?

Answer 30

up to 75,000 ybp radiocarbon dating is reliable. 14C isotope decays to 14N at a constant rate. Every 5730 years, half of the 14C will decay in 14N (half-life). After death - no more uptake of 14C so the ratio of 14C/14N gives estimate age.

Question 31

What is background extinction?

Answer 31

rates aren’t that high - - 95% of all extinctions are due to them - Caused by predation, competition, disease, combo of factors. - Endemic - native to only one area - extinctions more common - Endemic hotspots - regions that have numerous endemic species.

Question 32

What is predator induced extinction as a subtype of background extinction?

Answer 32

145-66 mya bivalve family Inoceramidae were prominent - then they went extinct with timing consistent with rise of brachyuran crabs (expert shell crushing predators that went through a radiation event), thought to be only animal capable of creating marks on bivalve fossils - currently 7000 species of brachyuran crabs.

Question 33

What is invasive predator extinction as a subtype of background extinction?

Answer 33

feral cats have contributed to extinction of 60 species - leading cause of death for birds in Canada.

Question 34

What is predation on islands as a subtype of background extinction?

Answer 34

introductions on islands have large impacts - ecological balance upset - potential for unintended downstream impacts.

Question 35

What is introduced predators and island extinctions as a subtype of background extinction?

Answer 35

rats introduced to 80% of global island groups - responsible for extinction of at least 100 insular species.

Question 36

What is competition and extinction as a subtype of background extinction? What did Andrew Knoll do?

Answer 36

Evolutionary lineages with improved adaptive traits can lead to competitive exclusion. Ex. NS for plants better adapted to capturing and processing sunlight and/or transporting water and key nutrients found overlap between dominant species in decline and new species that replace it as the dominant species. The new species has adaptations that allowed improved light capture and nutrient transport

Question 37

What is disease and extinction as a subtype of background extinction?

Answer 37

chytridiomycosis in amphibians in 2000s - caused by chytridiomycete fungus - interferes with ability to transport chemicals across epidermis - wiped out 30 species in Panama and problem in Australian rain forest.

Question 38

What is compounding effects and extinction as a subtype of background extinction?

Answer 38

two waves of human colonization of Hawaiian islands - 4000-1500 years ago from East Indies and 1500s from Europe. 90-110 of 125-145 bird species extinct since. Compounding effects of disease introduction, predator/competitor introduction and hunting by humans.

Question 39

What is mass extinction?

Answer 39

>50-75% of species lost across all major taxa across broad geographic range - caused by widespread phenomena - climate change, meteor strike etc. - At least 5 - maybe 8 over past 600 my - Some wiped out 90% of species - Most agree 6th mass extinction is occurring

Question 40

What are the Big 5?

Answer 40

``` Crustaceous (aka K-Pg) (~65 mya) Triassic (~200 mya) Permian (~250 mya) Devonian (~375 mya) Ordovician (~450 mya) ```

Question 41

Describe the crustaceous

Answer 41

Most recent mass extinction 50% of all genera disappeared including dinosaurs Iridium (rare on earth but common in asteroids) in rock layers at K-Pg boundary Caused by impact of 10 km diameter asteroid - caused particulate in air - blocked sun.

Question 42

Describe the permian

Answer 42

Largest mass extinction - 90% of all animals went extinct - land and sea. Thought to be caused by massive volcanic eruptions in Siberia - caused increase in Co2, global temp increased by 6C, increase in ocean acidity Organisms adapted to low oxygen levels survived.

Question 43

Describe the ordovician?

Answer 43

Second largest mass extinction - 85% of species and half of all marine species disappeared. 2015 - new evidence implicates changes in ocean chem associated with decrease in oxygen that caused an increase in dissolved metals.

Question 44

What is phyletic gradualism?

Answer 44

Darwin - Adaptations are result of slow gradual process where beneficial variant slowly increases in frequency - eventually leads to formation of new species ie. equine evolution. New species arise from gradual transformation of ancestral species through slow, constant change

Question 45

What is punctuated equilibrium?

Answer 45

Eldredge and Gould - Major evolutionary change occurs in rapid bursts of morphological and phylogenetic changes followed by periods of stasis (absence of change). ie. Cambrian explosion (543-490 mya) - spike in marine genera and species. Evidence from Burgess Shale in BC.

Question 46

Does punctuated equilibrium contradict Darwin?

Answer 46

No, it just suggests additional mechanism for evolutionary bursts.