Geographic variation in morphological traits is widespread and important to our current understanding of evolutionary processes. Although male genitalia are perhaps the most divergent morphological traits in animals, geographic variation in genital traits has received little attention and the mechanism driving such variation is unclear. The species isolation hypothesis of genital evolution makes explicit predictions about geographic variation in genitalia predicting patterns of genital divergence that reflect the risk of mating with related but incompatible species. The sexual selection and pleiotropy hypotheses, however, predict general levels of geographic variation that reflect divergent sexual selection pressures or genetic drift. To test these predictions, we investigated geographic variation in genital morphology in the praying mantid genus Ciulfina (Mantodea: Liturgusidae) using elliptic Fourier analysis. We found significant levels of geographic variation in the genital morphology of four Ciulfina species irrespective of the relative proximity of different populations to contact zones with other species. These results reject the species isolation hypothesis, and instead support either the sexual selection or pleiotropy hypotheses to explain patterns of genital evolution in this genus.
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