T5 - Adaptation

Question 1

What is adaptation? What are the 2 related meanings?

Answer 1

1) A heritable phenotype that allows individuals to perform some function which enhances their survival and/or reproduction (fitness) in their current environment

• A trait maintained by NS for its current function
• Note; this involved no requirements that the trait originally evolved by NS for this reason (feathers were not evolved specifically for flight - we simply observe they can be used for flight)

2. The process by which a NS causes the evolution of traits that improve the fit between an organism and its environment

• process that produces phenotypes that enhance the survival and reproduction of an organism in its current environment

Question 2

What is an example of adaptation?

Answer 2

The Jamaican bromeliad crab

• females raise young in pools of water at the base of bromeliad stems
• females will then chemically engineer the pools for the benefit of their offspring
• act as pool cleaners and remove decaying organic matter to maintain oxygen levels and add snail shells to raise the pH and calcium
• rain water does not contain as much Ca as sewater does
• the females fine tune the environment to better adapt and benefit the offsprings survival

Question 3

What are exaptations?

Answer 3

Structures that are currently adaptations but that evolved in a different context and were later co-opted for their current fitness enhancing function

Exaptations = adaptations that have arisen after a change in function (the trait did not originally adapt/evolve for that reason)

Question 4

What is an example of exaptation?

Answer 4

Feathers on birds did not evolve for flight

• birds evolved from theropods (dinosaurs)
• feathers evolved long before flight
• birds ancestors bodies were too large and could not use the feathers for flight, they were most likley used in some other context (theromregulation, camoflage…)

Question 5

What is acclimation/acclimization?

Answer 5

A process by which an individual organism adjusts to a change in its environment to minimize the effect of stressors and to maintain performance

• indivs cannot evolve, but they can acclimate, only populations/species can evolve
• generally rapid and reversible
• changes due to acclimation do not alter an indivs genotype ∴they are not passed onto offspring

Question 6

What are adaptationist fairy tales?

Answer 6

Untested and unsupported ‘explanation’ for the adaptive value of a phenotype

• in the absence of supporting evidence

Question 7

How would one detect adaptation? Give an example

Answer 7

Determining its function and showing that this function increases fitness in its current environment

Ex. oxpeckers on large animals

• it was found that oxpeckers actually dont eat lice consistently, but rather pick at the wounds and eat the blood
• this disproved the theory that they improve the ox’s fitness

Question 8

What is the comparative method?

Answer 8

Seeks to correlate differences among populations or species with variation in a presumed selective agent (differences in biotic/abiotic environments)

I.e. how different species correlate to their environment

Question 9

what is a reciprocal transplant?

Answer 9

Fitness of individuals is quantified in each of the two environments; local adaptation makes a clear prediction (population 1 does better at site 1 and population 2 does better at site 2)

• If both species do well at a particular site, its not local adaptation, this is simply the better habitat

Question 10

What are Darwinian demons?

Answer 10

The ‘ideal’ organism that could simultaneously maximize all aspects of fitness (begin breeding immediately after birth, produce many large offspring and continue to do so with no decline in performance)

Question 11

Why do we not see Darwinian demons?

Answer 11

1. Selection acts on existing variation;

• variation may be lacking for some certain phenotypes/adaptations
• selection does not create anything new (the ideal phenotypes)

2. Historical constraints;

• NS modifies phenotypes that are the product of past evolution
• an organisms evolutionary history can impact future evolution

3. Trade-offs;

• Traits can serve multiple functions and the optimal design for one function may differ from that for another
• can also be costly to produce and maintain
• organisms have only finite energy budgets = resources invested in one are therefore unavailable for another (energy spent looking for food cannot be used to reproduce)

4. Environments change;

• An organisms environment includes other organisms with which it interacts
• Prey and predator are constantly adapting to each other
• NS often favours traits that allow either or to ‘win’ interactions ∴diminishing adaptation in the other species

5. Other evolutionary processes;

• Genetic drift (bottlenecks and founder events), gene flow and recurrent mutation can cause maladaptation (they are not linked to variation in fitness)