Genomic evidence for divergence with gene flow in host races of the larch budmoth

Abstract

Ecological divergence in the face of gene flow has recently become implicated as a potentially important cause of speciation and adaptive radiation. Here, we develop a genomic approach to test for divergent selection in sympatric host races of the larch budmoth Zeiraphera diniana (Lepidoptera: Tortricidae). We analysed hundreds of amplified fragment length polymorphism markers in 92 individuals in sympatric and allopatric populations, and in two backcross broods used to map the markers to individual chromosomes. The results directly confirm the existence of natural hybridization and demonstrate strong heterogeneity between chromosomes in terms of molecular divergence between host races (the average level of divergence was F ST = 0.216). However, genomic heterogeneity was not found when we analysed divergence between geographically separated populations of the same host race. We conclude that the variance of the level of sympatric divergence among chromosomes is the footprint of divergent selection acting on a few linkage groups, combined with appreciable gene flow that homogenizes between-race variation at the remaining linkage groups. These results, coupled with other recent multilocus analyses of sister species pairs, demonstrate that selection-driven sympatric phase of genetic divergence in the presence of gene flow is a likely feature of speciation.

Genetic structure of the forest pest Hylobius abietis on conifer plantations at different spatial scales in Europe

“…For host-plant effect, we also considered the F st values that ARLEQUIN provided for each individual locus. Loci with Po0.05 for F st were considered significantly differentiated (Emelianov et al, 2004).…”

Natural selection in action during speciation

“…Significant heterogeneity in marker F st has been documented between ecologically divergent races (34)(35)(36)(37)(38), with the interpretation that F st outliers must be linked to loci affecting the phenotypic traits known to distinguish the divergent ecotypes, races, or subspecies. However, outlier analysis alone cannot reveal the cause of deviant F st values, and the conclusion that F st outliers must be associated with genes causing the most obvious differences between ecotypes is premature.…”

“…First, outliers are easy to find. Even in studies with just a few markers (3,34,35,50), 5% or more of tested markers are generally F st outliers. Taking 5% as a minimal estimate, this observation implies either that hitchhiking regions are large enough that they capture 5% of randomly chosen markers (3), or that so many genes are under divergent selection that 5 of them can be found with only 100 markers (56).…”

Linkage Maps of thedwarfand Normal Lake Whitefish (Coregonus clupeaformis) Species Complex and Their Hybrids Reveal the Genetic Architecture of Population Divergence

“…This remains challenging without knowledge of the genetic architecture, i.e., the number, location, and effect of genomic locations contributing to differentiation within and among populations or species (Rieseberg 1998;Orr and Turelli 2001). As genetic architecture may either promote or constrain divergence (Hawthorne and Via 2001), such genomewide perspectives are integral in working toward a complete understanding of the functional genomic response to the evolutionary processes incurred by populations as they diverge (Ting et al 2001;Emelianov et al 2004;Wu and Ting 2004).…”

“…This remains challenging without knowledge of the genetic architecture, i.e., the number, location, and effect of genomic locations contributing to differentiation within and among populations or species (Rieseberg 1998;Orr and Turelli 2001). As genetic architecture may either promote or constrain divergence (Hawthorne and Via 2001), such genomewide perspectives are integral in working toward a complete understanding of the functional genomic response to the evolutionary processes incurred by populations as they diverge (Ting et al 2001;Emelianov et al 2004;Wu and Ting 2004).Genetic linkage mapping approaches have several advantages for addressing these issues (Rieseberg 1998). Such an approach has led to the detection of genomic regions resistant to introgression (e.g., Rieseberg et al 1999;Rogers et al 2001;Lexer et al 2003), the identification of adaptive QTL, and the dissection of complex traits (e.g., Peichel et al 2001;Saintagne et al 2004) and has proven valuable for the mapping of gene expression profiles (expression QTL, e.g., Kirst et al 2005).…”