Evidence that stress-induced changes in surface temperature serve a thermoregulatory function

Changes in body temperature following exposure to stressors have been
documented for nearly two millennia, however, the functional value of this
phenomenon is poorly understood. We tested two competing hypotheses to
explain stress-induced changes in temperature, with respect to surface
tissues. Under the first hypothesis, changes in surface temperature are a
consequence of vasoconstriction that occurs to attenuate blood-loss in the
event of injury and serves no functional purpose per se; defined as the
Haemoprotective Hypothesis. Under the second hypothesis, changes in
surface temperature reduce thermoregulatory burdens experienced during
activation of a stress response, and thus hold a direct functional value;
here, the Thermoprotective Hypothesis. To understand whether
stress-induced changes in surface temperature have functional
consequences, we tested predictions of the Haemoprotective and
Thermoprotective hypotheses by exposing Black-capped Chickadees (n=20) to
rotating stressors across an ecologically relevant ambient temperature
gradient, while non-invasively monitoring surface temperature (eye region
temperature) using infrared thermography. Our results show that
individuals exposed to rotating stressors reduce surface temperature and
dry heat loss at low ambient temperature and increase surface temperature
and dry heat loss at high ambient temperature, when compared to controls.
These results support the Thermoprotective Hypothesis and suggest that
changes in surface temperature following stress exposure have functional
consequences and are consistent with an adaptation. Such findings
emphasize the importance of the thermal environment in shaping
physiological responses to stressors in vertebrates, and in doing so,
raise questions about their suitability within the context of a changing
climate.