Effects of cold, short day and melatonin on thermogenesis, body weight and reproductive organs in Alaskan red-backed voles.

This study examined whether cold, short day or melatonin causes reproductive regression and stimulates nonshivering thermogenesis in a subarctic rodent Clethrionomys rutilus. Red-backed voles born and raised at 23 degrees C and 22 h light per day (LD 22:2) at Fairbanks, Alaska (65 degrees N) were exposed in one of six groups to: 1) long day (LD 22:2), 23 degrees C, injected daily with melatonin or saline 2 h before lights out, 2) long day, 3 degrees C, injected daily with melatonin or saline, 3) short day (LD 8:16), 23 degrees C or 3 degrees C. Voles were tested for nonshivering thermogenesis (NST) prior to and after 8 wk exposure. Body weight, testes weight and female reproductive tract weight were assessed after 8 wk in long day and 12 wk in short day. NST was not altered by short day or melatonin but cold (3 degrees C) caused an increase in NST which was similar in long day and short day. Body weight of males and females was not affected by short day but was decreased by melatonin. Short day did not alter mean testes weight (about 20% voles regressed) but reduced mean female reproductive tract weight (more than 40% voles regressed). Melatonin reduced testes weight and female reproductive tract weight (more than 50% of voles of both sexes regressed). The results suggest that in northern red-backed voles: the pineal does not mediate seasonal changes in thermogenic capacity, the pineal may mediate reduction of body weight and regression of reproductive organs but, in addition to day-length, other cues or factors may be important, populations may exhibit variability in sensitivity of reproduction to photoperiod which could allow for opportunistic breeding.