Decoupling of differentiation between traits and their underlying genes in response to divergent selection

Abstract

We dissected the relationship between genetic differentiation (Q ST ) for a trait and its underlying genes (G STq , differentiation for a quantitative locus) in an evolutionary context, with the aim of identifying the conditions in which these two measurements are decoupled. We used two parameters (y B and y W ) scaling the contributions of inter-and intrapopulation allelic covariation between genes controlling the trait of interest. We monitored the changes in y B and y W , Q ST and G STq over successive generations of divergent and stabilizing selection, in simulations for an outcrossing species with extensive gene flow. The dynamics of these parameters are characterized by two phases. Initially, during the earliest generations, differentiation of the trait increases very rapidly and the principal and immediate driver of Q ST is y B . During subsequent generations, G STq increases steadily and makes an equal contribution to Q ST . These results show that selection first captures beneficial allelic associations at different loci at different populations, and then targets changes in allelic frequencies. The same patterns are observed when environmental change modifies divergent selection, as shown by the very rapid response of y B to the changes of selection regimes. We compare our results with previous experimental findings and consider their relevance to the detection of molecular signatures of natural selection.

Considering evolutionary processes in adaptive forestry

“…Noticeably, this local adaptation did not completely erode within-population genetic variation of adaptive traits (Mimura and Aitken 2007;Alberto et al 2013). The long-term maintenance of evolvability also depends on the genetic architecture of the traits under selection, and in the case of polygenic inheritance, Kremer and Le Corre (2012) showed that evolutionary changes first result from the selection of the fittest combinations of gene alleles before it reduces the allelic diversity at individual gene loci.…”

Evolutionary responses of tree phenology to the combined effects of assortative mating, gene flow and divergent selection

“…Finally, we assigned a range of values for those parameters that we purposely investigated: pollen migration models, level of divergent selection, intensity of stabilizing selection, degree of assortative mating and directions of environmental and genetic gradients ( Table 2). The range of values have been investigated through sensitivity analysis in earlier investigations using Metapop (Le Corre and Kremer, 2003;Kremer and Le Corre, 2011;Soularue and Kremer, 2012). In total, we considered 42 scenarios and ran 30 independent replicates over 1000 generations for each of them.…”

Evolutionary quantitative genomics ofPopulus trichocarpa

“…Yet, the majority of trait associated SNPs were not F ST outliers (S2 Table) and appeared to be unresponsive to selection for different climatic conditions, especially for phenology traits such as bud set, leaf drop or growth period. A previous simulation study suggested that differentiation in candidate loci is limited for complex traits in forest trees (i.e., their F ST values are similar to neutral values), despite their strong adaptive divergence among local populations (high Q ST ), due to large population sizes and high levels of gene flow [52]. Thus, highly polygenic adaptation (as observed in complex genetic traits) will not show sufficient allele frequency differentiation such that climatic clines in SNPs of candidate genes can be exhaustively detected.…”