Małgorzata M. Lipowska, Edyta T. Sadowska, Ulf Bauchinger, and Paweł Koteja
The locomotor performance achieved in a challenging situation depends not only on physiological limitations, such as the aerobic exercise capacity, but also on behavioral characteristics, such as adequate stress coping. The stress response is mediated largely by the hypothalamic-pituitary-adrenal (HPA) axis, through modulated release of glucocorticoids. We used a unique experimental evolution model system to test a hypothesis that evolution of an increased aerobic exercise performance can be facilitated by modification of the glucocorticoid-related stress coping mechanisms. Bank voles (Myodes glareolus) from “aerobic” (A) lines, selected for 22 generations for high maximum swim-induced rate of oxygen consumption (VO2swim), achieved a 64% higher VO2swim than those from unselected, control (C) lines. The temporal pattern of exercise during the swimming trial also evolved, and the A-line voles achieved VO2swim later in the course of the trial, which indicates a modification in the stress response characteristics. Both VO2swim and the average metabolic rate measured during the trial tended to increase with baseline corticosterone level, and decreased with the post-exercise level. Thus, increased baseline corticosterone level promotes high metabolic performance, but a high corticosterone response to swimming acts as an inhibitor rather than stimulator of intense activity. However, neither of the corticosterone traits differed between the A-selected and control lines. Thus, the experiment did not provide evidence that evolution of increased aerobic performance is facilitated by modification of the glucocorticoid levels. The results, however, do not exclude a possibility that other aspects of the HPA axis function evolved in response to the selection.