Interpopulation variability of endocrine and metabolic response to cold stress in northern red-backed vole ( Myodes rutilus )

The stresses faced by animals in nature are reflected in the adrenal cortex functional activity. It is possible to expect that the basal concentrations of glucocorticoid hormones will be increased in animals inhabiting unfavorable conditions (and correspondingly the value of the adrenocortical reaction to acute stress will be decreased). Since mobilization of the organism resources for the compensation of environmental challenges is the main function of the stress reaction, its weakening should result in a decrease in the reserve capabilities of metabolism. To check this assumption, the basal and maximal metabolic rates, body temperature, and corticosterone concentration in plasma measured before and after acute cooling in a helium–oxygen mixture were compared in northern red-backed voles (Myodes rutilus) from two populations differing in their relative abundance. It was found that, despite higher basal levels of corticosterone and decreased stress reaction values, individuals from the population of the forest park zone of Novosibirsk Science Center with a low relative abundance demonstrated a higher maximal metabolic rate than individuals from the mountain–taiga population with a high abundance. The results demonstrated that habitation in unfavorable conditions leads to elaboration of physiological adaptations that increase resistance to acute stress but increase the risk of the development of the chronic stress, which negatively influences adaptability.