Adaptive variation in the upper limits of avian body temperature

dc.contributor.authorFreeman, Marc Trevor
dc.contributor.authorCzenze, Zenon J.
dc.contributor.authorSchoeman, Keegan
dc.contributor.authorMcKechnie, Andrew E.
dc.date.accessioned2022-11-08T07:52:18Z
dc.date.available2022-11-08T07:52:18Z
dc.date.issued2022-06
dc.description.abstractPhysiological performance declines precipitously at high body temperature (Tb), but little attention has been paid to adaptive variation in upper Tb limits among endotherms. We hypothesized that avian maximum tolerable Tb (Tbmax) has evolved in response to climate, with higher Tbmax in species exposed to high environmental heat loads or humidity-related constraints on evaporative heat dissipation. To test this hypothesis, we compared Tbmax and related variables among 53 bird species at multiple sites in South Africa with differing maximum air temperature (Tair) and humidity using a phylogenetically informed comparative framework. Birds in humid, lowland habitats had comparatively high Tbmax (mean ± SD = 45.60 ± 0.58 °C) and low normothermic Tb (Tbnorm), with a significantly greater capacity for hyperthermia (Tbmax 2 Tbnorm gradient = 5.84 ± 0.77 °C) compared with birds occupying cool montane (4.97 ± 0.99 °C) or hot arid (4.11 ± 0.84 °C) climates. Unexpectedly, Tbmax was significantly lower among desert birds (44.65 ± 0.60 °C), a surprising result in light of the functional importance of hyperthermia for water conservation. Our data reveal a macrophysiological pattern and support recent arguments that endotherms have evolved thermal generalization versus specialization analogous to the continuum among ectothermic animals. Specifically, a combination of modest hyperthermia tolerance and efficient evaporative cooling in desert birds is indicative of thermal specialization, whereas greater hyperthermia tolerance and less efficient evaporative cooling among species in humid lowland habitats suggest thermal generalization.en_US
dc.description.departmentZoology and Entomologyen_US
dc.description.librariandm2022en_US
dc.description.urihttps://www.pnas.orgen_US
dc.identifier.citationFreeman, M.T., Czenze, Z.J., Schoeman, K. & McKechnie, A.E. Adaptive variation in the upper limits of avian body temperature. Proceedings of the National Academy of Sciences of the United States of America. 2022 Jun 28;119(26):e2116645119. doi: 10.1073/pnas.2116645119.en_US
dc.identifier.issn1091-6490 (online)
dc.identifier.issn0027-8424 (print)
dc.identifier.other10.1073/pnas.2116645119
dc.identifier.urihttps://repository.up.ac.za/handle/2263/88187
dc.language.isoenen_US
dc.publisherNational Academy of Sciencesen_US
dc.rights© 2022 the Author(s). Published by PNAS. This open access article is distrib- uted under Creative Commons Attribution License 4.0 (CC BY).en_US
dc.subjectMaximum body temperatureen_US
dc.subjectHeat tolerance limiten_US
dc.subjectAdaptive thermoregulationen_US
dc.subjectClimatic variationen_US
dc.subjectEndothermen_US
dc.titleAdaptive variation in the upper limits of avian body temperatureen_US
dc.typeArticleen_US

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