Recent studies suggest that animals are decreasing in size as a general response to global warming, for reasons that remain unclear. Here, by analysing ectotherm death time curves that take into consideration the intensity and duration of a thermal challenge, we show that heat tolerance varies predictably with size. Smaller animals can maintain higher body temperatures than larger ones during short periods, but cannot maintain higher body temperatures over long periods as their endurance declines more rapidly with time. Body size effects and adaptive variation in heat tolerance may have been obscured in the past by these unaccounted for temporal effects. With increasing size, thermal death occurs at relatively lower metabolic rates with respect to rest at a non-stressful temperature, which might partly explain the reported reductions in organism size with climate warming and shed light on the mechanisms that underlie scaling.
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The datasets and R computer scripts associated with this article are open access available in DRYAD (https://doi.org/10.5061/dryad.zkh189380).
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We thank M. Santos for discussions on the subject and insightful comments on a first draft. This work was partly funded by a ANID PIA/BASAL FB0002 grant and a FONDECYT grant no. 1170017 to E.L.R.
The authors declare no competing interests.
Peer review information Nature Climate Change thanks Félix Leiva and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary Fig. 1 Distribution of (a) measured and standardized Tcrit and (b) warming tolerance (warming tolerance = Tcrit - Tmax where Tmax corresponds to the mean temperature of the warmest month). Note that the standardization procedure tends to decrease not only mean Tcrit and warming tolerance but also their variance. Importantly, extreme values decrease to a substantially degree, ultimately increasing the signal-to-noise ratio of subsequent analyses. Tcrit was standardized for a 24 h exposure after accounting for mass effects.
Supplementary Fig. 2 Bias estimation in measured versus standardized Tcrit. (a) Reported critical temperature estimates Tcrit versus standardized values for a 24 h exposure after accounting for mass effects. (b) Difference between Tcrit before and affecter the standardization procedure, to obtain an estimate of bias, plotted against standardized Tcrit, which controls for confounding effects of variable exposure times and body size differences. Similar reported and standardized Tcrit fall on the dotted line in both panels.
Supplementary Fig. 3 Geographic variation in Tcrit and warming tolerance. Association between critical temperature estimates Tcrit and warming tolerance versus latitude and maximum temperature Tmax, estimated as the mean temperature of the warmest month. Upper and lower panels show replicated analyses for (a,b) reported versus standardized Tcrit for a 24 h exposure against absolute latitude, (c,d) Tcrit against maximum temperature Tmax and (e, f) warming tolerance estimated as Tcrit - Tmax along a latitudinal gradient.
Supplementary Figs. 4 Number of measurements per species in our dataset, showing that a few species in our analyses have been measured more than once (see main text).
Supplementary Figs. 5 Body size and time distribution in the two datasets employed in our analyses (n = 328 measurements for Dataset 1 and 309 for Dataset 2).
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Peralta-Maraver, I., Rezende, E.L. Heat tolerance in ectotherms scales predictably with body size. Nat. Clim. Chang. 11, 58–63 (2021). https://doi.org/10.1038/s41558-020-00938-y
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