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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.
173 views reported since publication in 2019.