Taxonomia e variação geográfica das populações de Helicops leopardinus (Schlegel, 1837) (Serpentes, Xenodontinae)

Abstract

Helicops leopardinus (Schlegel, 1837) is a waterskake species widepread in Cis-Andean South America from the Guianas to northern Argentina. Among its congeners, it is unique in having longitudinal rows of dark dorsal spots, as well as a chess-like ventral pattern composed of alternated bands. Most of the preliminary approaches in the literature suggest that the variations of quantitative and qualitative parameters of the H. leopardinus populations deserve more detailed investigations. In addition, the lack of a comprehensive morphological study throughout the range of this taxon prevents conclusive interpretations regarding local diferentiations that remain poorly understood. Herein, I present a taxonomic revision of the populations attributed to H. leopardinus based on external morphology (color pattern, body proportions and pholidosis) and hemipenial structure. I have examined 661 specimens from localities within the whole range of the target taxon throughout the several hidrographic basins of Cis-Andean South America, in all the morphoclimatic domains. As a result, I determined five Operational Taxonomic Units (hereafter OTUs) four of which objectively attributable to full species. The nominal form H. leopardinus (Schlegel, 1837), remains associated with the populations ocurring in the Amazon basin, the complex of basins of the Prata and southern Tocantins-Araguaia, as well as the region of contact among the Amazon, Tocantins-Araguaia and Atlântico Nordeste Ocidental basins (OTU 1); the name H. leprieuri Duméril et al., 1854 must be attributed to the populations from northeastern Brazil, in the São Francisco, Atlântico Leste and Atlântico Nordeste Oriental basins (OTU 2); finally, since there are no available names attributable to the OTUs 3 and 4, these entities must be described as new species. Our OTU 5, represented by only three female specimens from the region of Santa Fé Province, in Argentina, exhibits distinctly low subcaudal counts and sensibly high ventral counts, although the remaining observable features fit in all details with OTU 1. Therefore, I decided to provisionally lump both OTUs under the name H. leopardinus (Schlegel, 1837) until larger samples and further evidence (e.g., hemipenial morphology) allow more conclusive interpretations. As other aquatic taxa, the differentiation patterns associated not only with H. leopardinus, but also with other Hydropsini taxa, may respond to the history of the South American complexes of hidrographic basins representing important source of evolutionary and biogeographic information. Integrtative approaches including phylogenetic and phylogeographic analyses must be encouraged in order to test the patterns revealed by morphological data, as well as the classifcation proposed herein.