Evaluation of the cell population of the seminiferous epithelium and spermatic indexes of the bat Sturnira lilium (Chiroptera: Phyllostomidae)

Abstract

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 37.61×10(6) cells, and daily sperm production per gram of testis averaged 209.68×10(6) 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.

Figure 1. Sturnira lilium testis submitted to TUNEL technique.

Brown nuclei are positive to the TUNEL assay. a) Dry season. ST: Seminiferous tubule. Bar: 30 µm. Inset: pachytene spermatocyte going throw apoptosis. Bar: 10 µm. b) Rainy season. Arrow: Pachytene spermatocytes undergoing apoptosis. Bar: 20 µm. c) Negative control. Bar: 30 µm. d) Positive control. Bar: 30 µm.

Figure 2. Light microscopy of seminiferous tubules cross-sections in the beginning (a) and in the end (b) of stage 1 of seminiferous epithelium cycle in Sturnira lilium.

a) Dry season. PL/L: Preleptotene/Leptotene spermatocytes; PC: Pachytene spermatocyte; RS: Round spermatid; SC: Sertoli cell's nucleus. Bar: 30 µm. b) Rainy season. A: Type-A spermatogonia; ZG: Zygotene spermatocyte; PC: Pachytene spermatocyte; RS: Round spermatid. Bar: 20 µm.

Figure 3. Ultrastructure of the germ cells in stage 1 of the seminiferous epithelium cycle in Sturnira lilium.

a) Dry season. PL/L: Preleptotene/Leptotene spermatocytes connected by cytoplasmic bridge; →: Basal lamina; I: Interstitium. Inset: Cytoplasmic bridge. Bars: 3 µm. b) Dry season. SC: Sertoli cell's nucleus; _*: Sertoli cell's nucleolus; →: Basal lamina; I: Interstitium. Bar: 2 µm. c) Rainy season. →: Linear chromatin regions inside the nucleus of a leptotene primary spermatocyte. Bar: 2 µm. d) Rainy season. RS: Round spermatid nucleus; Ac: Acrosome. Bar: 5 µm.