Heterothermy as a mechanism to offset energetic costs of environmental and homeostatic perturbations

Abstract

Environmental and biotic pressures impose homeostatic costs on all organisms. The energetic costs of maintaining high body temperatures (Tb) render endotherms sensitive to pressures that increase foraging costs. In response, some mammals become more heterothermic to conserve energy. We measured Tb in banner-tailed kangaroo rats (Dipodomys spectabilis) to test and disentangle the effects of air temperature and moonlight (a proxy for predation risk) on thermoregulatory homeostasis. We further perturbed homeostasis in some animals with chronic corticosterone (CORT) via silastic implants. Heterothermy increased across summer, consistent with the predicted effect of lunar illumination (and predation), and in the direction opposite to the predicted effect of environmental temperatures. The effect of lunar illumination was also evident within nights as animals maintained low Tb when the moon was above the horizon. The pattern was accentuated in CORT-treated animals, suggesting they adopted an even further heightened risk-avoidance strategy that might impose reduced foraging and energy intake. Still, CORT-treatment did not affect body condition over the entire study, indicating kangaroo rats offset decreases in energy intake through energy savings associated with heterothermy. Environmental conditions receive the most attention in studies of thermoregulatory homeostasis, but we demonstrated here that biotic factors can be more important and should be considered in future studies.

Mitochondrial polymorphism m.3017C>T of SHLP6 relates to heterothermy

“…Mammalian species use heterothermy as a very effective energy-saving strategy to overcome harsh environmental conditions ( Morales et al, 2021 ). In addition to maintaining a T b of around 37°C during activity, heterothermic species are capable to enter controlled, hypometabolic phases of less or more than 24 h termed daily torpor or hibernation (multiday torpor), respectively ( Barnes et al, 1986 ; Hume et al, 2002 ; Sheriff et al, 2013 ; Ruf and Geiser, 2015 ).…”

Defining the link between oxidative stress, behavioural reproductive suppression and heterothermy in the Natal mole-rat (Cryptomys hottentotus natalensis)

“…One of the most well-known physiological adaptations to an abiotic stressor is the implementation of adaptive heterothermy in the Dromedary camel (Camelus dromedaries) in response to heat and dehydration stress (Schmidt-Nielsen et al, 1956). Heterothermy is one mechanism by which animals deal with variations in their environment to avoid heat and water stress and for energy conservation (Giroud et al, 2021;Giroud et al, 2020;Hetem et al, 2009;Morales et al, 2021;Oosthuizen et al, 2021). A heterothermic response includes the facultative, reversible decrease in metabolic rate (metabolic depression) and body temperature in response to the environment (ambient temperature and/or reduced availability of energy resources) (Lovegrove, 2000;McKechnie and Mzilikazi, 2011).…”