Seasonal changes in sperm parameters, testicular histology and circulating levels of reproductive hormones in the male African straw-colored fruit bat (Eidolon helvum)

Abstract

Objective: To investigate seasonal changes in some reproductive characteristics of the male African straw-colored fruit bat [Eidolon (E.) helvum] in a tropical rain forest area of South-East Nigeria. Methods: Spermatozoal characteristics in the testes and cauda epididymides, testicular histology, and the circulating levels of the reproductive hormones, testosterone, follicle stimulating hormone and luteinizing hormone were evaluated in male bats captured in late January (peak dry season), late May (early rainy season) and late September (late rainy season) of 2019. The bats were captured in Obiagu community in Enugu State, South-East Nigeria. Data were analyzed with analysis of variance. Results: There were high serum concentrations of testosterone in early and late rainy season and of luteinizing hormone in early rainy season, but the concentrations of both hormones were low during peak dry season. These hormonal changes corresponded with the testicular seminiferous and spermatogenic activities and testicular and epididymal sperm concentrations, which were also maximal during early and late rainy season but minimal during peak dry season. Epididymal sperm motility and vitality were also high in early and late rainy season but low in peak dry season, while sperm morphological abnormalities were low in early and late rainy season but elevated in peak dry season. There was histological evidence that spermatogenesis did not cease completely during testis regression, but continued at a reduced rate during the dry season. Conclusions: The findings do not support concurrent epididymal sperm storage with testis regression in E. helvum. Altogether, these indicate that seasonal changes significantly alter sperm characteristics, testicular histology and circulating levels of reproductive hormones in E. helvum within the study area.