Theory predicts that speciation rates should be accelerated in organisms undergoing sexual selection. In systems involving female choice, sexual selection acts directly on traits that may be important in prezygotic reproductive isolation, potentially fostering rapid divergence of such traits among allopatric populations. Despite the appeal of this concept, it has proven difficult to document. We provide genetic, behavioral, and simulation data illustrating that the striking and possibly recent divergence in traits of male behavior and morphology among populations of the jumping spider Habronattus pugillis can be attributed to sexual selection. We have found evidence for varying degrees of lower female response and offspring viability among some between-population crosses, consistent with the early stages of speciation. We have developed a gene-tree-based method for comparing phenotypic and genetic data sets to infer selection, and have found robust statistical evidence that directional selection has acted on male traits, by confirming that their rate of fixation exceeds that of neutral mitochondrial genes. Because these traits are apparent targets of female choice, the results indicate that sexual selection is driving divergence of phenotypes potentially crucial to the speciation process.
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