Meta-analysis of 47 studies: amphibians and reptiles from variable climates show stronger fever
Researchers at the University of São Paulo pooled data on 49 species: a 1 °C larger daily temperature range went with a ~0.45 °C higher rise in body temperature after an immune challenge.
Researchers at the Universidade de São Paulo (USP) led by Danilo Giacometti pooled the results of 47 earlier studies on behavioral fever in amphibians and reptiles, scinexx reports. The meta-analysis covers 49 species and 101 statistical effect sizes describing temperature responses after infection or other immune challenges. scinexx.de
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How the analysis was done
Many ectothermic animals can raise their body temperature deliberately, even though they produce little heat themselves. They do it by moving to sunlit surfaces or warmer parts of their habitat. This behavioral fever can support the body's defenses, but it requires suitable ambient temperatures. Until now it was unclear how strongly the temperature differences within a habitat affect the fever response of different species.
The team compared the body temperatures of treated animals with those of uninfected controls and accounted for relatedness between species. For wild-caught animals, the data were linked to climate values from their places of origin. In the statistical model, a mean daily temperature range larger by 1 °C went with a rise in body temperature after an immune challenge that was about 0.45 °C higher. The association persisted after body mass and evolutionary relatedness were taken into account.
Amphibians, reptiles and pathogens
The evidence for behavioral fever was clearest in amphibians. In the corresponding subanalysis, the average temperature increase in reptiles could not be established with statistical certainty. This was unexpected, because the permeable skin of frogs and other amphibians increases evaporation and water loss in warm conditions. "This contradicted our initial expectation, since reptiles are considered models of behavioral temperature regulation," Giacometti said. scinexx.de
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The type of immune challenge also mattered. Bacterial challenges produced a clearer fever response than experiments with fungi or viruses, for which the meta-analysis found no statistically supported effect. Bacterial experiments were far more common, however, so no general conclusion about all pathogens can be drawn.
Part of the difference between amphibians and reptiles may stem from test conditions: amphibians are often tested in humid laboratory settings, where seeking warmer spots costs less water than in the wild. The authors also point to differences between experimental setups and signs of bias from preferentially published positive results. The climate analysis reflects regional temperatures, not the small-scale warm spots actually available to each animal. The study did not examine whether the temperature rise improves survival. Whether habitat changes affect infection risk or survival must be clarified by further studies under natural conditions.
The original study was published in Proceedings of the Royal Society B: Biological Sciences (doi: 10.1098/rspb.2026.1712).
