local adaptation

Le Corre V & Kremer A 2003 Genetic variability at neutral markers, quantitative trait loci and trait in a subdivided population under selection. Genetics 164:1205-1219.

  • a quantitative model with additive effects was used to link genotypes to phenotypes
  • most of the variation resides within population whereas much higher population differentiation occurs for complex traits
  • we introduced the parameter θ = Σi Σj≠i COVij / Σi σi2
  • θ can be interpreted as a measure of disequilibrium of allelic effects among QTL, in contrast to disequilibrium measuring association of allelic states
  • most of the difficulties linked with the analytical treatment of selection on a multilocus trait in a subdivided population arise from the presence of genetic covariances among loci, at both the within- and the between-deme level
  • QST = ... = (1 + θB) FST / [(θB − θW) FST + 1 + θW] ... (5)
  • the differentiation for the selected trait QST will therefore take the same value as the allelic differentiation FST at QTL in two cases:
  • θB = θW = 0
  • θB = θW
  • the extent of genetic covariance at the within-deme level, as measured by the parameter θW, depended primarily on the intensity of selection
  • under complete allogamy, no or low linkage disequilibrium was maintained at the within-deme level, except when selection intensity was strong
  • HS and GST are basically single-locus measures, even though they are averaged over all QTL
  • VW and QST are multilocus measures, since they also include covariances generated by gametic disequilibria
  • for most traits ω2 / VE falls between 5 and 50
  • QST values were found to be much higher than GST values for neutral markers
  • diversifying selection seems to be the most common form of selection in natural populations
  • most of the loci contributing to the trait would exhibit GST values of similar magnitude to neutral markers
  • only a few would exhibit important allelic differentiation and important contribution to the between-deme variance of the trait
  • this pattern was caused by allele frequency changes at the QTL under both selection and population subdivision
  • evolution of a population toward a fixed optimum via sequential susbstitution of favorable mutations generally leads to such a pattern
  • there is clearly a need for more theoretical or simulation-based studies that consider the consequences of epistasis on the dynamics of genetic variability under natural selection