Abstract
BackgroundStudies of geographic variation can provide insight into the evolutionary processes involved in the early stages of biological diversification. In particular, multiple, replicated cases of geographic trait divergence present a powerful approach to study how patterns of introgression and adaptive divergence can vary with geographic space and time. In this study, we conduct replicated, fine-scaled molecular genetic analyses of striking geographic dewlap color variation of a Hispaniolan Anolis lizard, Anolis distichus, to investigate whether adaptive trait divergence is consistently associated with speciation, whereby genetic divergence is observed with neutral markers, or whether locally adapted traits are maintained in the face of continued gene flow.ResultsWe find instances where shifts in adaptive dewlap coloration across short geographic distances are associated with reproductive isolation as well as maintained in the face of gene flow, suggesting the importance of both processes in maintaining geographic dewlap variation.ConclusionOur study suggests that adaptive dewlap color differences are maintained under strong divergent natural selection, but this divergence does not necessarily lead to anole speciation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0763-4) contains supplementary material, which is available to authorized users.
Highlights
Studies of geographic variation can provide insight into the evolutionary processes involved in the early stages of biological diversification
We have shown in previous work that in two areas of contact, subspecies with different colored dewlaps show a reduction in gene flow, consistent with the expected signature of speciation [20]
Despite the homogenizing effects of gene flow, the maintenance of dewlap color variation at such a fine spatial scale suggests that strong divergent natural selection is acting on loci underlying dewlap color differences between spatially close sites while neutral regions of the genome are homogenized with gene flow
Summary
Studies of geographic variation can provide insight into the evolutionary processes involved in the early stages of biological diversification. Comparative studies of naturally replicated hybrid zones where adaptively divergent, closely related taxa come into contact and potentially interbreed can provide a powerful approach to study how patterns of introgression and adaptive divergence can vary with geographic space and time [7]. Studies of mice and lizards that adaptively vary in coloration for crypsis show that not all geographic transitions in color are associated with reduced gene flow [8, 10] This suggests that phenotypically different populations have yet to evolve barriers to reproduction, strong selection is acting to maintain phenotypic divergence, most likely from visual predators [12,13,14]
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