Flashcards in Adaptations Deck (32):
what is an adaptation (noun)?
specialized features that enhance fitness
what is an adaptation (verb)?
the process by which features that enhance fitness are fixed in a population or species
what is crypsis?
implying that something can stay hidden/camouflaged
the ability of an animal to avoid observation or detection by other animals
it may be either a predation strategy or an anti predator adaptation
methods include camouflage, nocturnality, subterranean lifestyle, and mimicry
what are some types of adaptations?
1) feeding specializations
3) mate attraction or competition
what are examples of mate attraction/competition?
- bright colors on male birds
- male to male combat with deer
- peacock feathers
what qualifies something as an adaption?
- improve fitness such that organisms WITH the trait have higher fitness than those without it
- show correlation between the presence of the feature and the hypothesized selective pressure --> does its presence correspond to a specific selective regime?
True or False:
natural selection is the only known explanation for adaption
natural selection leads to adaptations
drift can't lead to adaptation because its random, it has nothing to do with organisms surviving or reproducing better
True or False:
adaptations should be the result of evolution by natural selection
what is the relationship of causation between reproduction and fitness?
differential reproductive success and survival are the effect of differences in fitness
because of linkage among traits (pleiotropy) and passage of time, it can be complicated to evaluate WHAT selection has selected FOR (and thus it can be hard to determine whether something is an adaptation)
what is pleiotropy?
linkage among traits
when one gene influences two or more seemingly unrelated phenotypic traits
how can adaptations be identified?
by comparisons of related species specialized for different niches
how long does it take for adaptation to occur?
adaptation is (usually) gradual
gradual evolution of complexity
ex. mollusk, eyeballs
what is the gradual evolution of complexity?
Computer simulation (Nilsson & Pelger 1994)
- allowed eye parameters (shape, focal length, etc) to change by 1% per “mutation”
- required intermediates
-used quantifiable properties to measure the acuity of each model eye
Conclusion: it takes 400,000 generations to evolve complex vertebrate eye
what is an analogous structure?
similarity due to convergent evolution, not common ancestry
- analogous structures have independent evolutionary origins --> the same type of adaptation can evolve more than once
functionally similar, but structural and historically different
ex. vertebrate eye and octupus eye
ex. bat wing and bird wing
- product of convergent evolution
what is convergent evolution?
convergent evolution is the process whereby organisms not closely related independently evolve similar traits as a result of having to adapt to similar environments or ecological niches
usually caused by similar selective pressures
ex. human and octopus eye
inverted retina causing blind spot vs. non-inverted with no blind spot
what do similar selective pressures between species do?
they can cause convergent evolution
ABSENCE of selective pressure can also cause break-down and loss of pathways like animals that live in caves lose their eyesight and pigmentation
what is a homologous structure?
traits inherited by two different organisms from a common ancestor
structural similar, but can be functionally different
ex. the pentadactyl limb is a mammalian homology
ex. dolphin’s flipper, bird’s wing, cat’s leg, and the human arm
- can be products of divergent evolution
what is divergent evolution?
the accumulation of differences between groups which can lead to the formation of new species, usually a result of diffusion of the same species to different and isolated environments which blocks the gene flow among the distinct populations allowing differentiated fixation of characteristics
what is evidence for natural selection?
"poor design" is evidence for natural selection
The panda’s “thumb” is not homologous with
the human thumb…it is a makeshift adaptation for stripping bamboo that has evolved from a small bone in the wrist…not a “perfect” thumb
what is the gardener's dilemma?
when you are watering plants and walk around a tree and run out of hose, the sensible thing is to walk back around the tree
natural selection found another way by buying more hose and attaching it to the end to make the hose longer
what is a real life example of the gardeners dilemma?
the male urogenital system
the vas deferens are the tube that carries the sperm from testicles to penis --> in cold blooded animals it lies deep within the body cavity --> for warm blooded animals this is bad because sperm is temperature sensitive so overtime the testes migrates out of the body cavity to the scrotum --> along the way the testes took a wrong turn past the ureter and the vas deferens got hooked there like the gardeners hose --> so instead of unhooking the vas deferens, selection just made it longer
not a great design but it works
what are evolutionary anachronisms?
Evolutionary anachronism in plants, refers to those fruit, flower, leaf and stem attributes that evolved as an interaction with animals that are now extinct
many plants with large, tough seeds are not well adapted for seed dispersal at present because they depended on large herbivore dispersers that are now extinct
selective pressure changes!
what are vestigial structures?
structures with little or no current function, retained due to common ancestry
ex. the emu, rhea, ostrich, and kiwi all have evolved to be flightless but still retain tiny, functionless wings
penguins are also flightless BUT their wings have adapted to a new habitat and have been modified for swimming
ex. humpback whales have pelvic bones
ex. lizard has eyes even though it can't actually see
what is pre-adaptation? (exaptation)
an existing feature contributes significantly to an increase in fitness when selective landscape changes
what is preadaptation?
an existing structure modified to serve a new function
what is exaptation?
an adaptation that has arisen via preadaptation
original structure --> bird feathers for thermoregulation
new exaptation --> facilitates the evolution of flight
original structure --> salivary glands in snakes used for digestion
new exaptation --> facilitates the evolution of venom
original structure --> sweat glands for thermoregulation
new exaptation --> mammary glands for lactation
what is the fitness landscape?
a significant shift in the phenotype might push organisms "off and over" the adaptive peak
the hills in the landscape are several possible "good" solutions to selective pressures but the hills are separated by valleys of "bad" solutions
what are genetic constraints on adaptation?
heterozygote advantage: the form with the highest fitness can't "breed true"
in crested newts, theres two variants of a chromosome, 1A and 1B --> only those individuals with one of each variant, 1A/1B heteromorphs survive, all homomorphs, 1A/1A or 1B/1B, die before birth --> in each generation, half of the reproductive effort is wasted because 50% of the offspring are homomorphs
what are developmental constraints on adaptation?
developmental constraints: certain morphologies are impossible developmentally
the shape of a coiled shell can be described by three numbers: translation rate, expansion rate, distance from coiling axis
of all the possible shell shapes, only a small fraction are actually observed in nature
either these shell types have been consistently selected against or they are impossible to actually make because of some unknown developmental constraint
what is allometry?
it's a type of developmental constraint
something is allometric if it scales with size
in cervids, antler size is allometric --> a larger species will have not only an absolutely larger set of antlers but a relatively larger set of antlers
the extinct Irish Elk is thought to be near the developmental limit for antler/body size evolution because any further increase in body size would result in such a disproportionately large rack of antlers that it would exceed the weight that could be supported by the neck
what are trade-offs
constraints on adaptation
trade-offs are where an adaptation for one function may compromise another function
ex. in cheetahs, longer legs are good because then the cheetah is faster but then bones get brittle faster, it's a trade off
ex. in lizards they can have a few large eggs for fewer offspring or lots of small eggs with poor offspring survival --> so they can put energy into growth or reproduction --> so you can delay growth and grow slower and you live longer but then have few offspring