polygenic adaptation
Jain K & Stephan W 2017 Rapid adaptation of a polygenic trait after a sudden environmental shift. Genetics 206:389-406.
- we can observe evolution in action
- evolution can be so rapid that evolutionary and ecological timescales are confluent
- we consider a quantitative trait that is determined additively by a large number of diallelic loci of unequal effects
- the population is assumed to be infinitely large and to evolve under stabilizing selection and mutation
- we concentrate on the short-term period after the environmental change, which may be defined as the time until the phenotypic mean reaches a value close to the new optimum
- a trait z is determined by l diallelic loci
- the effect at each locus is assumed to be exponentially distributed
- neglecting dominance and epistasis, the trait z is determined additively
- selection is weak
- recombination rate is high
- linkage equilibrium (LE)
- testing for fast polygenic adaptation:
- using standardized frequencies, one can construct tests to detect SNPs that deviate strongly from a neutral population structure (e.g., Coop et al. 2010)
- this approach only works if there are relatively large extended gradients of ecological variables
- we expect that the allele frequency shifts between the parental and derived populations are relatively small
- it may be best to consider the frequency shifts of alleles simultaneously at all loci involved
- (instead of individual SNPs)
- this may be a promising approach, as all + alleles shift their frequencies in the same direction in the short-term phase, which should increase the power of the test