RESUMO
Myotis levis (yellowish myotis) is a small Neotropical insectivorous vespertilionid bat that provides valuable ecosystem services, such as control of disease vectors and agricultural pests. Aiming to describe the fluctuations of the reproductive organs throughout the year, the gonads and epididymis from 124 adult bats were histologically evaluated. These animals were captured in Santuário do Caraça, Minas Gerais, Brazil. After the initial screening, six bats per reproductive stage (in a representative month) had specific organs harvested for further investigation. The gonads, epididymis, accessory sex gland and brown adipose tissue were collected for biometric analyses. Furthermore, yellowish myotis testis was evaluated through histomorphometric and molecular assays, whereas blood samples were collected for hormonal analyses. The data were compared among the reproductive stages and correlated with rainfall distribution. As a result, we demonstrated that yellowish myotis presented a seasonal reproduction showing testis regression and rest, resembling the pattern exhibited by temperate-zone vespertilionid bats. During the Mature stage, after the peak of rainfall distribution, yellowish myotis testicles were fully developed for gamete production and maximum testosterone synthesis. These findings indicate a significant influence of this environmental factor on yellowish myotis reproduction. Following that, the accessory sex gland, brown adipose tissue and epididymis weights increased in the Regressed stage. The epididymis sperm storage occurred for at least 8 months and was observed in the Regressed, Rest and beginning of the Maturing stage. This reproductive fluctuation is interesting because the reactivation of the gonads coincided with the least amount of sperm in the epididymis.