W3 selection+ W4 limits change Flashcards
Why study natural selection?
Studying natural selection provides crucial info about the evolutionary foces that affect distribution and abundance of pops/species
What in the interspecific approach to studying natural selection?
comparative approach- compare 100s of species for traits of interest and infer selection from patterns of similairity/ divergence across species.
- inferences are limited if phylogeny not accounted for- account for by reducing likelihood that relatedness among species results in spurious associations between trait and enviro
what is the intraspecific approach to studying selection?
determines if natural selection is stronger than the neutral forces
- clinal studies
- whole genomes- Qst vs Fst to infer selection vs drift
- comparison of neutral vs adaptive genetic markers/ candidate genes
What are clinal studies?
clines are environmental gradients- constantly stable and implicate the action of natural selection
- genetically based clines in traits- result of evolved differences in response to climatic selection
Qst vs Fst definitions
Qst= differentiation in quantitative genetic traits
- can use common garden experiment to measure variation in these traits within and between populations
- provides a measure of how similar/diff pops are at quantitative genetic level
Fst= pop structuring/differentiation of neutral genetic varization
- gives insight on importance of drift
Qst vs Fst selection implications
- QST = FST – no selection, divergence due to drift
- QST ≠FST – selection is occurring
- QST > FST – divergent natural selection, populations differ
- QST < FST – uniform natural selection, populations similar
How can evolution be constrained?
- genetic correlation/ genetic covariances
- lack of genetic variation
What causes genetic correlation?
Genetic correlation can be due to;
1. Pleiotropy- same gene(s) controls two or more traits
2. Linkage disequilibirum- non- random association of genes
These can slow/ limit any evolutionary response to change
What is correlation r?
The degree to which two traits co-vary ie the variance of one trait is related to the variance of the other
What is genetic correlation?
degree to which two traits are affects by the same genes (pleiotropy) or pairs/groups of genes (linkage disequilibrium
Additive genetic correlation ra= measures the degree of transmission from parent to offspring
How is adaptive evolution constrained?
Genes that increase fitness in one environment reduce fitness in another, selection cannot simultaneously increase both traits (that are correlated)
What is a limit to evolutionary change?
lack of genetic variation- in absence of additive genetic variation evolution by natural selection is not possible
R= h2S if h2 zero or close to, selection will have little to no effect
What can changing environmental conditions do?
reveal significant levels of additive genetic variance
What is desiccation plasticity?
the extent to which species that are restricted to sensitive desiccation stress compared to those with widespread distribution and are much more resistant they are in their ability to increase their resistance in plasticity as opposed to evolution
