Internal morphology reveals reproductive isolation between two amphisbaenian closely-related species (squamata: amphisbaenidae)

Abstract

Comparing reproductive tract morphology between closely related species may reveal mechanisms and processes of reproductive isolation mainly associated to evolutionary divergence. Although the reproductive tract of amphisbaenians has been qualitatively described for some species, interspecific variation associated with mechanical reproductive isolation has been poorly investigated through clearly defined hypotheses. Interspecific differences in reproductive tract may be particularly interesting in amphisbaenians, because fossoriality has caused bilateral asymmetry in internal organs. In this study we compared reproductive tract morphology between two closely related Amphisbaenidae species (Amphisbaena anaemariae and A. silvestrii). We used multivariate approaches to test the general hypothesis that interspecific divergence in nine variables that quantify the reproductive tract explain mechanisms and processes of reproductive isolation associated with evolutionary divergence. Our hypothesis testing was focused on investigating levels of sex-dependence and bilateral asymmetry on interspecific reproductive divergence. We found bilateral asymmetry in most of the variables measured, and sex-dependent morphology of the reproductive tract in both sexes, despite this finding was less evident in females. Our results are mainly associated with a combination of evolutionary forces acting on bilateral asymmetry and sex dependent dispersal. Ultimately, this study provides insights into evolutionary processes based on reproductive isolation mechanisms in organisms for which sampling is hindered by fossoriality