Comparison of the Morphology and Histomorphometry of Spermatogenic Cyst of Three Sharks Species With Diametric Testes

Abstract

Characterization of the reproductive anatomy of elasmobranchs (sharks, skates, rays, and sawfish) offers unique insights into the evolution of reproductive traits in animals due to their phylogenetic position at the base of the vertebrate tree of life. Yet, despite advances in our understanding of male elasmobranch reproductive physiology and testes histology, very little is known about how testes histomorphometrics varies with male maturation. In this study, we characterize and contrast testes morphology and histomorphology of males at different maturation stages in three shark species with diametric testes development: Prionaceglauca, Rhizoprionodon lalandii, and Mustelus canis. All stages of spermatogenesis were observed in P. glauca and R. lalandii, while for M. canis, only males at early stages of maturation were examined and therefore all the spermatogenesis cells lineage were not present. The number of Sertoli cells increased with cell development by six times in R. lalandii and roughly four times in P. glauca, and were statistically different among stages of spermatogenesis cysts in both species. Statistical differences in cyst diameter and Sertoli cell numbers were observed between P. glauca and R. lalandii. The increase of spermatocyte II cell diameter described for R. Lalandii in this study was not usual to elasmobranch species as compared, for example, to P. glauca. This information proves the importance of studying the testicular development and the process of spermatogenesis is necessary for understanding the reproductive biology of the species, including life cycles and history, variation of reproductive morphology.