Análise do dimorfismo sexual em recém-eclodidos de Podocnemis Expansa (Schweigger, 1812)

Abstract

Most chelonian pups do not have sexual dimorphism. This condition is also faced by Podocnemis expansa, requiring the use of invasive methods or even euthanasia of individuals for sexing. Considering that this species has a long history of population decline and that sex ratio is an important variable to support conservation and management practices, the present study aimed to analyze the efficiency of geometric morphometry in the sexing of newly hatched P. expansa individuals when compared to their histological sexing. A total of 78 specimens from natural nests located along the Xingu River, between Vitória do Xingu and Senador José Porfírio Counties, in the southwestern part of the State of Pará, Brazil, were used. For the morphometric analysis each specimen had its carapace photographed and the softwares TPSUtil, TPSDig2 and TPSRelw were used to generate the data matrix used in the analyses. For the histological study the specimens had their gonads removed and sexual identification was performed by means of light microscopy. Data analyses were conducted in the Past 2.17 software. The histological analysis revealed the presence of 38 female and 40 male specimens. The morphometric analysis provided accurate sexual identification for approximately 50% of the specimens. Thus, base on the performed tests, this technique did not generate satisfactory results that could replace or even reduce the use of the histological studies for the sexing of newly hatched P. expansa individuals. Therefore, histology turned out to be the best tool for identifying the sex in the assessed population of the studied chelonian species.