Sex-Dependent Divergence In Asymmetrical Reproductive Tract Morphology Between Two Closely-Related Amphisbaenian Species (Squamata: Amphisbaenidae)

Comparing reproductive tract morphology between closely-related species may reveal mechanisms and processes leading to reproductive isolation and cladogenesis. Differences in external morphology are often inconspicuous between closely-related Neotropical species, and tissue samples for DNA sequencing are usually scarce for fossorial organisms such as amphisbaenians. Therefore, comparing characters of the reproductive tract between closely related amphisbaenians may be a viable alternative to understand processes by which evolutionary lineages have diverged morphologically from common ancestors. In this study we used multivariate ordination to compare reproductive tract morphology between two closely-related Amphisbaenidae species (Amphisbaena anaemariae and A. silvestrii), which are morphologically similar, and phylogenetically closely related. We tested the hypothesis that interspecific divergence in the reproductive tract may explain mechanisms and processes of reproductive divergence leading to evolutionary divergence. Our results suggest that divergence between two closely related Amphisbaenidae species may be linked with reproductive isolation caused by morphological differences in the reproductive tract. However, the levels of divergence detected varied between sexes and sides of the body on which the variables were measured, with vas deferens length, testis length and diameter and gonad-cloaca length as the determining variables differencing species. Although our findings must be validated by DNA-based analysis, this study provides insights into evolutionary processes based on reproductive divergence mechanisms in organisms for which sampling is hindered by fossoriality.