title: What role does natural selection play in speciation?
abstract: If distinct biological species are to coexist in sympatry, they must be reproductively isolated and must exploit different limiting resources. A two-niche Levene model is analysed, in which habitat preference and survival depend on underlying additive traits. The population genetics of preference and viability are equivalent. However, there is a linear trade-off between the chances of settling in either niche, whereas viabilities may be constrained arbitrarily. With a convex trade-off, a sexual population evolves a single generalist genotype, whereas with a concave trade-off, disruptive selection favours maximal variance. A pure habitat preference evolves to global linkage equilibrium if mating occurs in a single pool, but remarkably, evolves to pairwise linkage equilibrium within niches if mating is within those niches--independent of the genetics. With a concave trade-off, the population shifts sharply between a unimodal distribution with high gene flow and a bimodal distribution with strong isolation, as the underlying genetic variance increases. However, these alternative states are only simultaneously stable for a narrow parameter range. A sharp threshold is only seen if survival in the 'wrong' niche is low; otherwise, strong isolation is impossible. Gene flow from divergent demes makes speciation much easier in parapatry than in sympatry.
authors.affiliation: Institute of Science and Technology, Am Campus 1, 3400 Klosterneuburg, Austria. nick.barton@ist.ac.at
authors.forename: N H
authors.initials: NH
authors.lastname: Barton
mesh_terms: D000818:Animals; D005075:Biological Evolution; D017753:Ecosystem; D005260:Female; D051456:Gene Flow; D049810:Genetic Speciation; D005828:Genetics, Population; D015810:Linkage Disequilibrium; D008297:Male; D008957:Models, Genetic; D009154:Mutation; D011995:Recombination, Genetic; D012098:Reproduction / Q000235:genetics; D012641:Selection, Genetic