Natural selection in action during speciation

Abstract

The role of natural selection in speciation, first described by Darwin, has finally been widely accepted. Yet, the nature and time course of the genetic changes that result in speciation remain mysterious. To date, genetic analyses of speciation have focused almost exclusively on retrospective analyses of reproductive isolation between species or subspecies and on hybrid sterility or inviability rather than on ecologically based barriers to gene flow. However, if we are to fully understand the origin of species, we must analyze the process from additional vantage points. By studying the genetic causes of partial reproductive isolation between specialized ecological races, early barriers to gene flow can be identified before they become confounded with other species differences. This population-level approach can reveal patterns that become invisible over time, such as the mosaic nature of the genome early in speciation. Under divergent selection in sympatry, the genomes of incipient species become temporary genetic mosaics in which ecologically important genomic regions resist gene exchange, even as gene flow continues over most of the genome. Analysis of such mosaic genomes suggests that surprisingly large genomic regions around divergently selected quantitative trait loci can be protected from interrace recombination by ''divergence hitchhiking.'' Here, I describe the formation of the genetic mosaic during early ecological speciation, consider the establishment, effects, and transitory nature of divergence hitchhiking around key ecologically important genes, and describe a 2-stage model for genetic divergence during ecological speciation with gene flow. divergence hitchhiking ͉ ecological speciation ͉ reproductive isolation

A linkage disequilibrium perspective on the genetic mosaic of speciation in two hybridizing Mediterranean white oaks

“…Therefore, the cluster definitions need to take into account the different scales of genome coverage if comparisons between both types of studies are to be made. Data from Renaut et al (2013) clearly illustrate this issue, as the 0.3-0.6 cM outlier clusters from their study must be different to the 20 cM clusters used to define DH (Via and West, 2008;Via, 2009) and the 10 cM clusters found in this study. One concern regarding outlier clusters is co-variation among linked loci (Nosil and Feder, 2012;Faria et al, 2013).…”

“…GH is caused by genome-wide effects of divergent selection on the effective number of migrants, and its magnitude is proportional to the survival probability of the migrants, their mating success, and the survival probability and the mating success of the F1. These terms have multiplicative effects and their product depresses gene flow equally across the entire genome (Via, 2009(Via, , 2012.…”

“…Subsequently, we genotyped 29 additional markers to saturate five regions from four LGs harboring putatively selected loci (in LGs #2,3,8 and 12). We hypothesized that DH would produce clustering of outliers (Via and West, 2008;Via, 2009); therefore, we expected to find a larger proportion of new outliers among the 29 additional markers.…”

“…Via (2009Via ( , 2012, proposed that strong divergent selection acting on a few loci generates an inter-population process, which she called divergence hitchhiking (DH), that is characterized by reduced inter-population recombination and gene flow. Only reduced recombination between groups around divergently selected genes would contribute to the length of the DH regions.…”

Did sex chromosome turnover promote divergence of the major mammal groups?

“…Views on the mechanisms of speciation, therefore, focused on the Muller‐Dobzhansky model, whereby accumulation of small mutations in populations that were physically separated promoted divergence 5, 6. Decades of work, primarily on Drosophila melanogaster , identified such ‘speciation genes’, whose mutation was associated with hybrid incompatibility, and similar genes are now found in many other organisms 7.…”