Melatonin influences the reproductive physiology of male pallid bats

Adult male pallid bats collected in July were maintained in photoperiods that provided 14 or 10 h of light/day (long or short days) and implanted subcutaneously with empty or melatonin-filled Silastic capsules. By early September, long-day bats treated with melatonin had smaller testes, larger accessory gland complexes and were more likely to have epididymal sperm than long-day bats which received empty capsules. In addition, in September, melatonin-treated animals weighed more than untreated animals. Melatonin simulates the effects of short days on testicular spermatogenesis and epididymal sperm storage in this species. We suggest that sensitivity to photoperiod in pallid bats, as in several other mammals, is mediated by the pineal gland.