Reproductive Importance of Brown Adipose Tissue in the Neotropical Sperm-Storing Vespertilionid Bat Yellowish Myotis:...

The Neotropical yellowish myotis reproduces seasonally, presenting four reproductive stages. During the reproductive cycle, a fluctuation occurred in the activity of the brown adipose tissue with a mass decrease in the Maturing and Mature stages, coinciding with higher serum testosterone levels. To investigate the importance of reproductive parameters, lipid composition, and androgenic function of brown adipose tissue, a machine learning model trained on a comprehensive dataset ranked reproductive parameters across stages. Additionally, twenty-four male adult bats were collected in Santuário do Caraça, Minas Gerais, Brazil, for lipid extraction and cell culture analyses. The Machine Learning/Shapley additive explanations method revealed that the brown adipose tissue was the third most important reproductive parameter for classifying bats in the reproductive stages. Brown adipose tissue lipid composition showed increased free fatty acids and decreased diacylglycerol, triacylglycerol, and free cholesterol in the Maturing and Mature stages, correlating with elevated serum testosterone levels. The brown adipose tissue produced testosterone in all reproductive stages and stimulated TM3 Leydig cells, with significant increases in the Mature and Regressed stages. These results suggest that brown adipose tissue may support Leydig cell steroidogenesis through the provision of free cholesterol, potentially facilitating testosterone production in the yellowish myotis.