Physiological diversity in thermoregulatory traits has been extensively investigated in both endo- and ectothermic vertebrates, with many studies revealing that thermal physiology has evolved in response to selection arising from climate. The majority of studies have investigated how adaptative variation in thermal physiology is correlated with broad-scale climate, but the role of fine-scale microclimate remains less clear . We hypothesised that the heat tolerance limits and evaporative cooling capacity of desert rodents are correlated with microclimates within species-specific diurnal refugia. We tested predictions arising from this hypothesis by comparing thermoregulation in the heat among arboreal black-tailed tree rats (Thallomys nigricauda), Namaqua rock rats (Micaelamys namaquensis) and hairy-footed gerbils (Gerbillurus paeba). Species and populations that occupy hotter diurnal microsites tolerated air temperatures (Ta) ~ 2–4 ℃ higher compared to those species occupying cooler, more thermally buffered microsites. Inter- and intraspecific variation in heat tolerance was attributable to ~ 30% greater evaporative water loss and ~ 44 % lower resting metabolic rates at high Ta, respectively. Our results suggest that microclimates within rodent diurnal refugia are an important correlate of intra- and interspecific physiological variation and reiterate the need to incorporate fine-scale microclimatic conditions when investigating adaptative variation in thermal physiology.
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We thank the Mathews family for allowing us to conduct this research at Radnor Farm, and A.F. Probert for assistance during the capture of animals. We thank Black Mountain Mine for allowing us to conduct research on their property in the Koa River Valley and K. Smit of Vedanta Resources for his assistance and support.
This project was jointly funded by the SARChI chair of Mammal Behavioural Ecology and Physiology (Grant number 64756) and the SARChI chair of Conservation Physiology (grant 119754) awarded to NCB and AEM, respectively. Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Research Foundation.
No competing interests are declared.
All methods were approved by the University of Pretoria Animal Ethics Committee (protocol EC019-18) and South African National Biodiversity Institute's Research Ethics and Scientific Committee (protocol P18/12).
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van Jaarsveld, B., Bennett, N.C., Kemp, R. et al. Heat tolerance in desert rodents is correlated with microclimate at inter- and intraspecific levels. J Comp Physiol B 191, 575–588 (2021). https://doi.org/10.1007/s00360-021-01352-2