Ultrastructure of the reproductive system of the black swamp snake (Seminatrix pygaea). VII. spermatozoon morphology and evolutionary trends of sperm characters in snakes

This study investigates the evolution of snake spermatozoa within a phylogenetic context, with the addition of a new ultrastructural description from the spermatozoa of the Black Swamp Snake, Seminatrix pygaea. Overall the spermatozoon of S. pygaea is similar to that described for other squamates, whereas some characters such as the electron lucent space separating the cortex and medulla of the acrosome complex may be a unique feature of S. pygaea spermatozoa. This preliminary analysis of sperm evolution within Serpentes leads to the hypothesis that some sperm characters are more plastic than others. Incongruencies are found between the molecular and the morphological topologies utilized, and the phylogeny derived from a morphological data set recovers more unequivocal ancestral states of snake sperm structure. Characters such as the beginning of the fibrous sheath at mitochondrial tier one unite the Colubroidea, whereas characters such as the presence of an acrosome vesicle subdivision, absent vacuity subdivision, and round ⁄ oval mitochondria in transverse section unite all squamates. However, from this analysis it is evident that more taxa need to be studied and taxa with current data need to be more thoroughly investigated to make more conclusive remarks regarding the evolution of sperm structure within snakes.