Seasonal changes in spermatogenesis (including germ cell degeneration) and plasma testosterone concentration in the grey-headed fruit bat, pteropus poliocephalus

Maximal testicular size of P. poliocephalus occurred during the February–March–April period (autumn breeding season) associated with maximal plasma levels of testosterone (121·5 ± 23·4 nmol/I). Testicular size decreased after the breeding season concomitant with a decrease in plasma testosterone (7·6 ± 1·7 nmol/I). Histologically, regressive changes were observed in the testis after the breeding season including a decrease in seminiferous tubule diameter and a decrease in Leydig cell nuclear diameter. Significant germ cell loss occurred during the breeding season (44%) mainly during the final spermatogonial division and meiosis and increased in regressed testes (69%), being accentuated chiefly at meiosis. All regressed testes showed some sperm production although it was much reduced after the breeding season; however, optimal fertility appears to be restricted to autumn by the large increases in testosterone secretion which only occur at this time.