Annual changes in serum testosterone levels and spermatogenesis in the hokkaido brown bear ursus arctos yesoensis

Tsubota, T.; Kanagawa, H.

Journal of the Mammalogical Society of Japan 14(1): 11-18


Accession: 007021669

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In 4 adult male Hokkaido brown bears (Ursus arctos yesoensis) in captivity, serum testosterone levels gradually began to increase from February in the middle of the torpor period, attained to a peak in April (6.8 ng/ml) or May (5.6 ng) after arousal, and decreased rapidly to the baseline value (below 1.0 ng) in June at the middle of the mating season; the low level lasted into January at the first half of the torpor period. The testis sizes in March to August (4.94 .+-. 0.34 cm; N = 17) were larger than those in September to February (4.23 .+-. 0.30 cm; N = 17) (p < 0.001). Active spermatogenesis was sustained from February to September in the 4 male captives and confirmed also in 14 adult male bears shot by hunters during the March-May period. Thus, it was revealed that the duration of active spermatogenesis was longer by .apprx.4 months than that of the high serum testosterone level, and that the male reproductivity (spermatogenesis) generally continued longer than did the female receptivity restricted to the mating season from early May to early July.