Seasonal changes in the thermoregulation of laboratory golden hamsters during acclimation to seminatural outdoor conditions

Abstract

Proper adjustments of the thermoregulatory mechanisms ensure survival in the natural environment. In the present study, we tested the hypothesis that laboratory golden hamsters ( Mesocricetus auratus) housed under seminatural outdoor conditions are able to acclimatize to daily and seasonal changes in the environment despite their long history of breeding in captivity. The animals experienced natural changes in the photoperiod and ambient temperature characteristic for central Poland. During experiments in the thermal gradient system, the daily rhythms of body temperature (measured as the temperature of brown adipose tissue, T BAT), preferred ambient temperature ( PT a) and activity were measured in summer, autumn and spring. We found that mean T BAT was highest in autumn and least in summer, reflecting seasonal changes in the capacity for nonshivering thermogenesis (NST). In summer, T BAT followed the robust daily rhythm with the amplitude of 1.1±0.1 °C. This amplitude was depressed in autumn (0.2±0.1 °C) and partially restored in spring (0.4±0.1 °C). Seasonal changes in the daily amplitude of T BAT recorded during both transitional periods, i.e., in autumn and spring, seem to be associated with hamsters' hibernation. In autumn, mean daily PT a was lower than in summer and spring, indicating the lowering of a set point for core body temperature ( T b) regulation. Locomotor activity was much higher in spring than in summer and autumn, and it always predominated at night. We conclude that laboratory golden hamsters housed under seminatural conditions express daily and seasonal changes in the thermoregulatory mechanisms that, despite long history of breeding in captivity, enable proper acclimatization to seasonally changing environment and ensure successful hibernation and winter survival.