Sperm ultrastructure of Bothrops alternatus and Bothrops diporus (Viperidae, Serpentes), and its possible relation to the reproductive features of the species

Abstract

Sperm ultrastructure has been described for several species of Serpentes and other Squamata in which it has been considered a valuable character source for phylogenetic studies. However, some ultrastructural traits have been also reported as adaptations to increase motility and/or longevity under sperm competition and storage conditions. Bothrops alternatus and Bothrops diporus are medium sized, viviparous, highly venomous species, and their reproductive cycles include periods of female sperm storage between mating and fertilization. In this work we provide, for the first time, a detailed ultrastructural description of the spermatozoa of B. alternatus and B. diporus and discuss its possible relation to their reproductive features. Sperm was obtained from the vas deferens, and was processed to obtain transmission electron micrographs and fluorescence micrographs. Spermatozoa of these species show similar morphological traits, which are closely related to the general model described for the Serpentes. Furthermore, several synapomorphies for the squamates can be identified in these cells. Nevertheless, the observed midpiece elongation and absence of dense bodies could augment the energy producing capabilities of the spermatozoa, thus enhancing the competitive aptitude of the ejaculate.