Natural Selection

The process by which species evolve and develop traits which increase their fitness

• Traits that enhance an organism's ability to survive and reproduce is an adaptation, which results from natural selection.
• Example - Bird of paradise tail and coloration are not related to natural selection (sexual selection instead), it's not really an adaptation? Depends on definition
• Adaptations to avoid inbreeding, which causes inbreeding depression (susceptibility to diseases, reduction in overall genetic diversity, genetic bottlenecks)
• Functional Traits are ways to group and measure adaptations

Trait evolution beyond adaptation

• traits under selection evolve after producing greater net fitness afterbalacing costs and effects
  • In eusocial organisms, traits can evolve to affect the fitness of other organisms that are closely related (altruism)

Three components of Darwin's theories

1. There is trait (phenotype) variation among individuals

• By measuring these traits we can study this variation
  • morphological, physiological, behavioral, Life History Adaptations, molecular
• Example given of timing of growth patterns in trees varying latitudinally (budburst, growth cessation, bud set in oak, birch, pine, spruce)

2. Trait variation results in fitness variation among individuals

A. Reciprocal transplants to test for local adaptation

• Local provenances of Pinus sylvestris were transplanted to different latitudes and the amount of growth wasmeasured over 13 years
• The trees grew better when they were grown in the area where the seeds were collected due to their adaptation to the summer-winter differential

B. Color polymorphism in peppered moths

• melanistic morph is more common in industrialized areas of England with soot

C. Dispersal ability in dandelion papus

• behavioral / life-history
• Selective agent is Competition avoidance, inbreeding avoidance and "bet hedging" or diversifying portfolio
• Varies in population size, extinction rate
• A similar experiment with dispersal of C. elegans showed that individuals with greater dispersal suffered less extirpation events

3. Trait variation is inherited from one generation to the next

• This is crucial for the theory of evolution - only traits which can be inherited will contribute to evolution and speciation
• Trait values have a genetic and environmental component
  • Only the genetic component is inherited
• The environmental component can be random (noise), predictable (plasticity) or shared (common environment i.e. maternal effects)