Lecture 6: Adaptation and comparative method

Adaptation

a feature which evolved due to natural selection it enhances Darwinian fitness in a given environment

darwinian fitness

the ability of organisms to survive and/or reproduce.

This is an organisms' way to evolve to become better at doing particular things such as resisting cold, finding food or avoiding predation

Sexual Selection

this is a mode of natural selection which organisms choose mates due to attraction of the desired mate. Think about a peacock's tail where it serves no survival purpose but it serves reproductive purpose. The prettier the tail, the "better" the mate

Physiological adaptation

an individual's phenotypic adjustment to environmental conditions

Evolutionary adaptation

This is adaptation that is permanent because the DNA sequence or genetic heritable trait was passed down from parent to offspring. The heritable trait is advantageous over an extended generation through generation

Phenotypic plasticity

the ability of an organism to physiologically change itself

Think about a muscle where if you keep working out a muscle, it will change and grow because of all the stress that was put on it

What are the three conditions that are driving adaptive evolution

1. phenotypic variation is always present
2. this variation often affects darwinian fitness
3. traits are heritable in the narrow sense

What are the main factors that affect phenotypic evolution

1. random mutation and genetic drift
2. immigration/emigration and gene flow
3. sexual selection

Genetic drift

the change in frequency of an existing gene variant in the population due to random chance

Gene flow

the movement of genes into or out of a population due to migration of individual organisms that reproduce in their new populations, or to the movement of gametes

How can we recognize adaptations

1. specifying the selective agent or agents that favor a trait
2. showing that the trait in question has evolved through natural selection. Contains a historical origin that maintains function over several generations
3. elucidating the components of and the sequence of steps to the final (complex) adaptive state

Preadaptation

possession of the necessary properties to permit a shift into a new ecological niche or habitat

What are the 4 general approaches of studying adaptation and there significance?

1. comparative method which shows what has happened in past evolution
2. Biology of natural populations shows the extent of individual; variation, heritability and genetic correlation, natural and sexual selection, field manipulations and intros. Shows the present evolution in action
3. Selection experiments and experimental evolution - shows, experimentally, what might happen during future evolution
4. comparison of real organisms with predictions of theoretical models - shows how close selection can get to producing optimal solutions

What are the general steps for the comparative method

1. obtain phylogeny from a source
2. obtain data on one or more phenotypic traits of interest
3. Map traits onto tree and use maximum parsimony to infer how many changes have occurred and where on the tree and then compare traits of species by statistics

What are the limitations of two species comparative studies

1. independent variable is confounded with species membership

2. species almost always will differ. Heres why
a. process of speciation may result in genetic differentiation that affects phenotypic traits
b. the two species will have experienced little or no genetic exchange since the time of their evolutionary divergence
c.their ancestors will have experienced different environmental conditions so sometimes its bad to compare


3. degrees of freedom - should be 0 when there is a correlating trait with environment but its usually not. and this happens if you keep adding more species comparison

4. you don't know which state or trait was ancestral

What are the general steps for comparing multiple species

1. develop questions or hypotheses
2. measure several species for some phenotypic trait and calculate mean
3. characterize environmental features that should indicate variation in the "selective regime"
4. then relate traits to each other

phylogenetically based methods allow one to

1. Avoid statistical problems caused by non-independence
2. learn more from the data such as infer ancestral states, compare rates of evolution across lineages, test for "outlier" species
3. make better choices as to which species should be compared