Rapid divergent evolution of internal female genitalia and the coevolution of male genital morphology revealed by micro-computed tomography

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Animal genitalia are thought to evolve rapidly and divergently in response to sexual selection. Studies of genital evolution have focused largely on male genitalia, with our understanding of female genital evolution relatively limited. The paucity of work on female genital morphology is likely due to problems faced in quantifying shape variation, due to their composition and accessibility. Here we use a combination of micro-computed tomography, landmark-free shape quantification, and phylogenetic analysis to quantify the rate of female genital shape evolution among 29 species of Antichiropus millipedes, and the coevolution of male genitalia. We found significant variation in female and male genital shape among species. While male genital shape showed significant phylogenetic signal, female genital shape did not. Male genital shape was found to be evolving 1.2 times faster than female genital shape. Female and male genital shapes exhibited strongly correlated evolution, indicating that genital shape changes in one sex are associated with corresponding changes in the genital shape of the other sex. This study adds novel insight into our growing understanding of how female genitalia can evolve rapidly and divergently and highlights the advantages of three-dimensional techniques and multivariate analyses in studies of female genital evolution.

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External Organisations
Western Australian Museum