Circannual cycles in golden-mantled ground squirrels: Lengthening of period by low temperatures in the spring phase

Summary

Two complementary experiments were designed to study the effect of cold temperatures on the spring phase of the circannual cycle of golden-mantled ground squirrels (Spermophilus lateralis). In the first experiment, a group of animals was kept in a warm room (22 °C) until the latter half of their weight-loss hibernation phase. They were then placed in a cold room (3 °C) for about 2 1/2 months, after which they were returned to the warm room. The control group was kept in the warm room throughout the experiment. The exposure to cold delayed both subsequent body weight peaks and the end of molt by about 6 weeks. In the second experiment, ground squirrels that had been transferred to a warm room (21 °C) from a cold room (6 °C) while still in their weight-loss hibernation phase reached peak body weights 6 weeks earlier than a group transferred after hibernation had ended. These results show that cold temperatures in the spring phase alone can produce a lengthening of the circannual cycle that is of similar magnitude to that found previously when animals are kept continuously in the cold.