Taxonomia do gênero Leposoma (Squamata, Gymnophthalmidae) na bacia do rio Madeira, Amazonas, Brasil, e o papel dos rios na variação morfológica de Leposoma osvaldoi Avila-Pires, 1995

Abstract

The distribution of different organisms in the Amazon, mostly birds and primates, is delimited by the presence of large rivers, specially were sister species substitute themselves in their opposite banks. Recently, the role of major river tributaries, mainly the Madeira River, is being demonstrated. Few studies analyzed the role of rivers in the distribution of Amazonian lizards. This work examined if the rivers in the Brazilian portion of Madeira basin are delimiting the distribution of geographic variants in the lizard Leposoma osvaldoi (Squamata, Gymnophthalmidae). The geographic variation in the specimens analyzed is determined by measures of head scales. The scales were measured from digital photographs, a new approach in the taxonomy of the genus Leposoma. The success of the methodology in identifying and quantifying the diagnostic characters between species was tested in two sympatric species that occur in the Madeira Basin, Leposoma percarinatum and Leposoma osvaldoi. One hundred and sixteen specimens, 81 of L. osvaldoi and 35 of L. percarinatum, distributed over 21 localities, were analyzed. The two species differ mostly in the dimensions of interparietal, length of second supraocular, width of frontoparietal, anterior width of frontal and suture between prefrontals. In L. osvaldoi, there is a strong sexual dimorphism in head width, explaining the dimorphism shown in the width of some head scales. The Madeira, Aripuanã and Roosevelt rivers probably delimit the occurrence of distinct populations in L. osvaldoi, recognized by the dimensions of the interparietal scale, frontal length and size of the suture between frontoparietals. Larger samples from critical localities still would be necessary to clarify the variation pattern in this region and start to evaluate their possible cause.