Spatial self-structuring accelerates adaptive speciation in sexual populations

QUESTIONS: How does spatial self-structuring influence the waiting time until adaptive speciation in a population with sexual reproduction? Which mechanisms underlie this effect?
MODEL: Using a spatially explicit individual-based multi-locus model of adaptive speciation, we investigate the evolution of a sexually reproducing population, with different levels of spatial self-structuring induced by different distances of natal dispersal. We examine how the waiting time until speciation is affected by the mobility of individuals, the number of loci determining the phenotype under disruptive selection, and the mating costs for individuals that prefer rare phenotypes.
CONCLUSIONS: Spatial self-structuring facilitates the evolution of assortative mating and accelerates adaptive speciation. We identify three mechanisms that are responsible for this effect: (i) spatial self-structuring promotes the evolution of assortativity by providing assortative mating "for free", as individuals find phenotypically similar mates within their spatial clusters; (ii) it helps assortatively mating individuals with rare phenotypes to find mating partners even when the selected phenotype is determined by a large number of loci, so that strict assortativity is difficult; and (iii) it renders speciation less sensitive to costs of assortative mating, especially for individuals that prefer rare phenotypes.
KEYWORDS: Adaptive speciation; Assortative mating; Frequency-dependent selection; Homogeneous habitat; Mating cost; Multiple loci; Spatial self-structuring; Waiting time until speciation

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