Adaptive population divergence: markers, QTL and traits

Molecular markers appear to be poor indicators of heritable variation in adaptive traits. Direct comparison of population structure in markers with that in traits is made possible by the measure Qst, which partitions quantitative genetic variation in a manner analogous to Fst for single gene markers. A survey of the literature reveals that mean Qst is typically larger than and poorly correlated with mean Fst across 29 species. Within species, Qst varies widely among traits; traits experiencing the strongest local selection pressures are expected to be the most divergent from molecular Fst. Thus, Qst will be particularly relevant to conservation efforts where preserving extant adaptation to local environments is an important goal. Recent theoretical and simulation studies suggest however that Fst is a better predictor of the pattern of allelic differentiation at quantitative trait loci (QTLs) than is Qst in random mating populations, in which case allelic variation at QTLs might be better assessed by molecular markers than will extant variation in the traits themselves.