Gonadal and photoperiodic control of seasonal body weight changes in male voles.

After 15 wk in a short photoperiod (10 h of light/day), adult male voles weighed 25% less and consumed 33% less food than did voles in a long photoperiod (14 h light/day). Neither body weight nor food intake differed among long- and short-day castrated voles. After 19 wk, castrated long-day voles weighed less than did intact animals. Voles reduced their body weight during the first 15 wk in the short photoperiod and increased their body mass during the succeeding 15 wk. Body mass of short-day voles was positively correlated with combined testes weight. Voles in the short photoperiod collected less nesting material than did their long-day counterparts at week 31. Pelage characteristics at week 32 were not affected by castration or by photoperiod. We conclude that the decreased body mass of male voles during the late summer, fall, and early winter reflects a decrease in circulating levels of testicular hormones; gonadal recrudescence and increased circulating androgen levels are in part responsible for the subsequent seasonal increase in body weight. Part of the increased body mass in late winter in field populations or in laboratory voles after 15 wk in the short photoperiod is independent of the resumption of gonadal activity. Fluctuations in neural and endocrine processes, rather than availability of food, are the principal factors underlying seasonal changes in energy balance.