Evolution of the cloacal and genital musculature, and the genitalia morphology in liolemid lizards (Iguania: Liolaemidae) with remarks on their phylogenetic bearing

Abstract

In this study, we describe the intra-and interspecific anatomical variations of cloacal and related muscles of male and female genitalia in species of five iguanian genera (three liolemid: Ctenoblepharys, Liolaemus, and Phymaturus plus Diplolaemus leopardinus and Tropidurus melanopleurus as outgroups). We found variations (seventeen characters) in topology, origin and insertion areas, tendon morphology and size of the musculature of this region. We also describe the variations of hemipeneal morphology, which is especially notable for the hemipenis of C. adspersa, D. leopardinus, and T. melanopleurus, as this is first time they are described in the literature. Among the most significant findings are the identification of three new muscles, two of them inserted on the roof of the cloacal chamber (anterior and posterior cloacal retractor) and the third inserted superficially in the floor of the cloaca, just before anterior to the precloacal glands row (superficialis cloacalis retractor). We report sexual dimorphism in seven muscle characters. Musculature related to hemiclitoris is reduced in proportion to its size in comparison to the degree of development of male genitalia and associated musculature. The evolution of characters was traced on the known phylogenetic hypotheses of relationships among families. Characters taken from the cloacal/genital myology bring similar support to the liolaemid tree even rooting the analysis using different outgroups. In addition, a phylogenetic study using only myological characters was performed. In this case, C. adspersa was found to be more related to Liolaemus species instead of being basal to Liolaemus plus Phymaturus.