Among all bat species, Desmodus rotundus stands out as one of the most intriguing due to its exclusively haematophagous feeding habits. However, little is known about their spermatogenic cycle. This study aimed at describing the spermatogenic process of common vampire bats through testicular histomorphometric characterization of adult specimens, spermatogenic production indexes, description of stages of the seminiferous epithelium cycle and estimative of the spermatogenic process duration. Morphometrical and immunohistochemical analyzes for bromodeoxiuridine were conducted under light microscopy and ultrastructural analyzes were performed under transmission electron microscopy. Vampire bats showed higher investment in gonadal tissue (gonadosomatic index of 0.54%) and in seminiferous tubules (tubulesomatic index of 0.49%) when compared to larger mammals. They also showed a high tubular length per gram of testis (34.70 m). Approximately half of the intertubular compartment was found to be comprised by Leydig cells (51.20%), and an average of 23.77x106 of these cells was found per gram of testis. The germline cells showed 16.93% of mitotic index and 2.51% of meiotic index. The overall yield of spermatogenesis was 60% and the testicular spermatic reserve was 71.44x107 spermatozoa per gram of testis. With a total spermatogenesis duration estimated at 37.02 days, vampire bats showed a daily sperm production of 86.80x106 gametes per gram of testis. These findings demonstrate a high sperm production, which is commonly observed in species with promiscuous mating system.

Due to the scarcity of information about patterns of spermatogenesis in bats, this study aimed to provide information on the testicular activity of the bat Sturnira lilium along the annual seasons. Thus, a series of morphometrical and stereological analyses were made using the testes of adult S. lilium in order to achieve a better understanding of the sperm production dynamics. Light and transmission electron microscopy analyses were performed in testicular fragments of animals captured during dry and rainy seasons. The testes followed the pattern of organization described for other mammals, and there were no morphological differences between organs collected either in dry or in rainy seasons. Each tubular cross-section in stage 1 was made of 0.5 type-A spermatogonia, 4.4 primary spermatocytes in preleptotene/leptotene, 3.7 in zygotene, 11.9 in pachytene, 35.6 round spermatids and 8.5 Sertoli cells. The mitotic and meiotic indexes were 15.4 and 2.9 cells, respectively, while the spermatogenesis yield was 68.7 cells. The testicular sperm reserves was 37.61×106 cells, and daily sperm production per gram of testis averaged 209.68×106 cells, both highest averages occurring in the rainy season. S. lilium male bats have a continuous reproductive pattern, high spermatogenesis yield and low support capacity by the Sertoli cells.

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Environmental factors can influence the reproductive rates in bats, and since morphometric information of bats testis is scarce, we aimed to compare the organization and quantification of the intertubular components in the testes of the bat Molossus molossus, collected in different seasons. Testicular histological sections were evaluated using light and electron microscopy. The intertubular compartment occupied an average 10% of the testes, being predominately constituted of Leydig cells (LC). The percentages of the testes occupied by the intertubular compartment and by LC were significantly higher in summer, while the other intertubular components did not vary significantly among the seasons. As suspected under light microscopy, the ultrastructural analysis confirmed the existence of multinucleated LC during winter. The increase in the nuclear percentage of LC in winter seems to have caused the decrease of the cytoplasmatic measurements in that season, as well as in the volume of LC. The highest cytoplasmatic values and volume of LC registered in the spring, summer, and fall can be related to greater activity of this cell in these seasons. The higher investment in intertubular tissue and in LC observed in summer, compared to winter; suggest an increase in the steroidogenic capacity of this bat during summer. The analyses correlating testicular morphometry and abiotic environmental factors in this study confirm the influence of climatic factors on the reproduction of M. molossus.