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