Chapter 8 - Adaption and Selection in the Wild Flashcards
What is the additive effect of an allele?
A difference between its homozygote and a midpoint between two homozygotes, i.e. a value genotype gains by replacing one allele with the allele in question, the “raw” value of an allele.
What is additive genetic variance?
Va, the proportion of Vg that is due to additive effects. Va is the basis for how populations respond to selection.
What maintains variation for quantitative traits?
Selection varies, meaning some phenotypes are best at certain times. Selection also favors rare genes (different levels of resistance) and, over a long term, the mutation-selection balance, or new genes being generated continuously.
What is GxE?
Genotypes not responding to the environment the same way, or Genotype x Environment interaction.
What is the norm of reaction?
The set of all such phenotypes across a range of environmental conditions.
What is phenotypic plasticity?
When a genotype alters it’s phenotypic expression of traits in response to different environments. Also a type of non-genetic variation.
What is an example for the evidence of costs?
Sticklebacks repidly evolving reduced defenses in lakes lacking predators.
Weeds rapidly evolving herbicide resistance, like the rapid evolution of glyphosate resistance.
What are the costs to defense?
If they are cheap, easy, and quick to evolve, most populations evolve and keep them.
If they are costly to develop and maintain, counter selection eventually reduces them where they are not needed.
What is a cost, or trade-off, to resisting pesticides in weeds?
Resistance can reduce fitness from 10-15%. This is common and explains the reversion once pesticides are removed.
What is a refuge and how can it slow the evolution of resistance?
Let’s use an example… BT toxin kills moth larvae. Moths then selected to resist this, but will revert back when no BT is present. Creating BT-free refuges will favor susceptible insects, thus slowing the evolution of resistance.
What is one way we can limit the strong selection for pesticide resistance in weeds?
By also planting susceptible varieties alongside.
Why is the galapagos a great place to study evolution?
Small populations make it easy to mark and follow individuals, a very ecologically simple system with a few species of birds and plants and few migrants, and the historical impact.
Where did Darwin’s finches come from and how did we figure it out?
We used molecular systematics. Using sequences of DNA in 2 outgroup species with 13 D.F species, we saw that:
- the common ancestor between both Darwin’s and Cocos finches was a grassquit (meaning that the theory that they evolved from Cocos finches is not true)
- convergence and hybridization occured
What is the common ancestor of Darwin’s Finches?
The grassquit genus Tiaris. The initial adaptive radiation occurred in the Carribian, spread to Central and South America, and then arrived on the Galapagos 2.3MYA.
What was the significance in variation of beak size?
It influences the efficiency with which birds can eat certain seeds. During drought, there were more big woody seeds, which favored birds with larger beaks.
