adaptation 1 - limits to adaptation Flashcards
quantitative traits
show that phenotype is influenced by both genetics and the environment (will be elaborated later)
Possible origins of a trait OTHER than adaptation
Adaptation
MORE than “useful” or “optimal”
Refers to a PROCESS of evolution
Def 1: A TRAIT or an integrated set of traits that has evolved by natural selection
Def 2: A PROCESS in which the traits of a population change over generations (evolve), resulting in individuals that are better able to survive and/or reproduce
Possible forms of evidence for adaptation
Show that the process of natural selection established the trait in a population
the adaptive landscape
There are many ways an organism can adaptive to it’s environment
Natural selection sees only variation currently in the population rather than distant possible phenotypes
Phenotype is a function of…
genetic (including additive genetic effects, dominance effects, and interaction effects) and environmental factors
traits are imperfect because…
factor of genetic and env factros
CONT SLIDE 7
Can be by products of other present or past processes ex. human chin, menstruation, colour of blood
look at cartoon slides
Example of assumptions of adaptation
regarding coloration of katydids as an adaption for camoflage from predators:
katydids preferentially occur on lichens
there are other possible colours they could be
predators see colour the way we do
colouration is genetically controllec
General assumptions of adaptation
The selective pressure we see now was still acting in the past when the trait evolved
Direction of causality
Don’t know if trait arose BECAUSE of the habitat, or if the trait allowed species to colonize those habitats
Exaptation
a trait originally evolved for one purpose, which is later co-opted for a different function
ex. feathers
How to demonstrate a trait is being maintained or established by natural selection
- Establish that there is variation among individuals in population
- Establish that traits are heritable (genetic)
3a. The traits affect function related to the proposed selective mechanism
3b. There are measurable effects of the trait on survival or reproduction
3a and b are related to natural selection requirement that diff. in fitness between individuals with different traits
Ancestral Constraints
Traits inherited from an ancestor that are difficult to change, and which are suboptimal or limit subsequent adaptation
ex. lungs evolved to supplement respiration through gills therefore not an issue that pathways of air and food through mouth crossed
Ancestral constraints in humans
Crossing of food and air pathways
Pelvic girdle - small size, originally AOK for eggs to pass through, however human babies are much larger than this
