Spermatozoa epididymal maturation in the Mexican big-eared bat (Corynorhinus mexicanus)

Prolonged epididymal sperm storage in vespertilionid and rhinolophid bats, provides an interesting experimental model for the study of spermatozoa epididymal maturation. We examined the presence of the cytoplasmic droplet, and the sequential induction of capacitation and the acrosome reaction in spermatozoa obtained from different epididymal regions (caput, corpus, cauda) throughout the annual reproductive cycle of Corynorhinus mexicanus (C. mexicanus). This is a vespertilionid bat that stores spermatozoa in the epididymis for several months after testes regression. The number of sperm recovered from the different epididymal regions indicate that epididymal transit in C. mexicanus is rapid. The persistence of a high percentage of sperm cells with cytoplasmic droplet in cauda epididymis was observed in addition to a low index of capacitation and acrosome reaction in sperm cells obtained from the corpus epididymis. There was a significant increase in the percentage of capacitated and acrosome reacted spermatozoa during the storage of sperm cells in the cauda epididymis and the percentage of capacitated spermatozoa was consistently, and significantly, higher (p < 0.05) in cauda compared to the corpus epididymis at all studied dates. The process of epididymal maturation in C. mexicanus is completed in the caudal region of this organ encompassing a significant period. Our results also indicate that in C. mexicanus, and in other vespertilionid and rhinolophid bats that show the same temporal asynchrony in the function of male reproductive organs, the final phases of epididymal maturation and storage are, apparently, independent of testicular function.