Spermatogenic cycle of a tropical rattlesnake Crotalus durissus (Squamata, Viperidae): Characterization, duration of seminiferous epithelium cycle and daily sperm production

Spermatogenesis is a biological process that occurs inside the seminiferous tubules and results in the production of highly specialized cells, the spermatozoa. The Neotropical rattlesnake Crotalus durissus is a medical-importance snake species that presents a seasonal reproductive pattern. Here we characterized for the first time the spermatogenesis of a Neotropical snake species. Testes of 15 mature male specimens of C. durissus were evaluated. Through histomorphometry analyses was determined that around 94 % of the testis parenchyma is occupied by seminiferous tubules. Seminiferous epithelium in rattlesnake is composed of different generations of germ cells that are organized in eight stages of the seminiferous epithelium cycle (SEC). The sperm release occurs at stage II and a multi-stage pattern was observed in this species. Surprisingly, two rounded spermatids generations were present from stage I to IV. Using the proliferation cell marker BrdU (bromodeoxyuridine), the duration of spermatogenesis was calculated based on the most advanced germ cell labeled, which was established at 40.80 days. High efficiency of Sertoli cell associated with a short duration of SEC rendered a powerful sperm production observed for C. durissus. These features indicate a well-established adaptation of this species to reach an enormous number of gametes, which is one of the various mechanisms developed to guarantee survival and maintain the genes passing over the next generations.

Simple summary

All species have one main goal, which is to pass their genes over to the next generations. In order to do that, males and females produce specialized cells that combined, will allow the generation of a new life. The male gamete, the spermatozoon, is produced inside the testes in a process named spermatogenesis. Besides it has been described for many species, especially mammals, little is known regarding the spermatogenesis of snakes. Thus, the present study revealed that rattlesnakes’ spermatogenesis is such organized as in humans. While in other animals only one generation of rounded spermatids is part of the spermatogenic stage, in rattlesnakes were observed two generations of rounded spermatids present in 4 out of 8 stages of the seminiferous epithelium cycle. The existence of the extra generation of rounded spermatids results in approximately one additional cycle for spermatogenesis completion. However, the total duration of spermatogenesis, which means the time to produce the spermatozoa, still stands among the fastest ones, being around 41 days. Also, the additional germ cell population resulted in a high Sertoli cell support capacity. These parameters have a strong influence over the daily sperm production, which reaches more than 100 million spermatozoa per gram of testis.