Abstract
Physiological regulation of body temperature, set at a high level, is one of the key features of endothermic homeotherms, such as birds and mammals. However, many mammals and some birds have evolved the ability for temporal down-regulation of core body temperature. We investigated how variation in environment temperature and habitat primary productivity determine variation in daily body temperature down-regulation among mammalian species. Nearly half of the variation in minimum daily body temperature among species was explained by variation in both primary productivity and environmental temperature. Mammals expressing low minimum body temperature inhabited regions of low annual temperature with wide daily and seasonal temperature variation. Simultaneously, those regions were characterized by low productivity and low seasonality in productivity. Furthermore, regions characterized by a high level of among-year variation in environmental temperature, but not in primary productivity, were inhabited by species with low minimum body temperature, but only by those adapted to relatively humid conditions. Our results suggest that daily heterothermy can be selectively advantageous in the environmental circumstances when high energetic demands for maintaining endothermic homeothermy, physiological regulation of a high and stable body temperature, cannot be supported. The results corroborate the hypothesis that mammals that have evolved daily down-regulation of body temperature may have higher chances of surviving extinction events caused by climatic changes. Therefore, daily heterothermy adaptation in contemporary mammals represents a mechanism for surviving the ongoing global warming.
Highlights
Physiological regulation of body temperature is a key aspect of mammalian and avian biology (McNab 1978, Lovegrove 2017, Rezende et al 2020)
We showed that the environmental predictors of primary productivity and environmental temperature, can determine the minimum body temperature observed in mammals
Minimum body temperature results from down regulation of physiological processes that can indicate the intensity of expressed heterothermy (Brown & Bartholomew 1969, Körtner & Geiser 2000)
Summary
Physiological regulation of body temperature is a key aspect of mammalian and avian biology (McNab 1978, Lovegrove 2017, Rezende et al 2020). Maintaining high and stable body temperature over fluctuating environmental conditions, known as endothermic homeothermy, has probably contributed to the ecological and evolutionary success of birds and mammals (Nespolo et al 2011). Torpor in mammals the circumstances when high energetic demands for maintaining endothermic homeothermy, a physiologically regulated high and stable body temperature, cannot be fulfilled (Hetem et al 2016, Dammhahn et al 2017, Lovegrove 2017). The high and stable core body temperature of endothermic homeotherms provides an optimal environment for enzymatic reactions, enables development of a complex nervous system, and allows a high reproductive rate, among other benefits (Nespolo et al 2011, Preußner et al 2017). How environmental variation affects heterothermy is still debatable (Vuarin & Henry 2014, Levesque et al 2016, Dammhahn et al 2017)
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