EGRU-blog

Comparative studies of quantitative trait (Qst) and neutral marker (Fst) differentiation have provided useful framework to detect local adaptations and study evolution. Albeit the framework has proven very fruitful and became refined several times over the past decade, some fundamental problems have kept plaguing it. In a paper now accepted for publication in Genetics, we outline a new and greatly enhanced framework to differentiate in between drift and selection as a cause of population differentiation.

The multipart-figure below illustrates some of the qualities of this approach. In this figure, the different shaped symbols represent population centroids and the ellipses ancestral G-matrices for the given set of populations. Different colors refer to populations residing in different selective regimes. In (a) and (b), the populations have diverged due to drift alone: populations cluster according to their ancestry and within the space demarcated by ancestral G. In (c) and (d), populations have diverged due to local adaptation: symbols clusters according to color (=selection pressure) and not by ancestry. It is also worth pointing out that in examples (c) and (d), Fst = Qst, which means that traditional methods would have been unable to detect the action of selection. In (e), we see a case where populations have been subject to stabilizing selection (Qst < Fst; i.e. populations have diverged due to directional selection). The case (f) represents the classical situation where population divergence has occurred due to action of directional selection (Fst < Qst).

The main point here to note is that this method allows detection of signatures of selection also in the case where Fst =Qst: the selection in these cases (c,d) is inferred from the fact that population centroids tend to cluster according to selective regime (color) rather than their ancestry (shape of the symbol). It is also worth pointing out that the new method accounts for many other technical problems that have plagued traditional Fst-Qst comparisons. Read the paper and become enlightened!

Ovaskainen O., M. Karhunen, C. Zheng, J.M. Cano Arias & J. Merilä (2011) A new method to uncover signatures of divergent and stabilizing selection in quantitative traits. Genetics, in press.