Bigger Day-Night Temperature Swings Mean Bigger Amphibian Fevers

What does this change for cold-blooded animals?

Practically, the findings point to habitat quality. Animals from more variable climates showed an enhanced capacity to raise their body temperatures after infection — which means access to a range of thermal options, warm spots and cool ones, may be part of an animal's immune toolkit.

"This result highlights the importance of preserving thermal heterogeneity, as animals that can explore different thermal resources may be better equipped to deal with immune challenges than those that live in thermally stable habitats," Giacometti said.

In plain English: a wetland or forest with varied microclimates — patches of sun and shade, warm shallows and cooler depths — may give sick animals a fighting option that a thermally uniform habitat doesn't. Flatten the landscape, and you may flatten the fever.

What the study doesn't say

Two gaps deserve attention.

• The analysis did not test whether behavioral fever actually improves survival after infection. Bigger fevers were observed, not proven beneficial.
• The amphibian-versus-reptile difference might reflect how studies are designed rather than how animals behave.

Both limits are preliminary-study caveats in the classic sense. The pattern is real across dozens of species. The interpretation still has room to move.

Where the research came from

Giacometti started the project after finishing his Ph.D. in Canada and returning to Brazil.

"When I finished my Ph.D. in Canada, I knew I wanted to move back to Brazil," he said. "I reached out to Professor Carlos Navas and suggested a postdoctoral project aimed at understanding how immune challenges influenced the thermal biology of amphibians and reptiles."

The project included both a meta-analysis and experimental work. The meta-analysis became this paper.

The team also accounted for shared traits between closely related species, a standard statistical safeguard that prevents a few well-studied branches of the family tree from dominating the result. The meta-analytical framework, Giacometti noted, lets researchers observe general patterns while estimating potential sources of bias in the data set.

What's next?

The science didn't stop at publication. Giacometti, now an assistant professor at the University of São Paulo, has students running follow-up experiments on frogs and lizards.

"I have an honors student currently exploring how closely related species of lizards that come from different habitats in Brazil (warm-dry and cool-wet) differ in their thermoregulatory responses to bacteria," he said. He also plans to recruit graduate students to study how environmental humidity mediates thermoregulatory responses to immune challenges in frogs.

That humidity question goes straight at the study's most puzzling result — amphibians febrile despite their leaky skin. If humidity shapes fever behavior in frogs, the dehydration puzzle may start to resolve.

There's history behind all this. Since the 1970s, data have suggested the physiological pathways behind fever are relatively conserved across animals, vertebrate and invertebrate alike. Seminal work in lizards argued that seeking warmth when sick has adaptive value — potentially helping animals not just fend off infections but become immune to them. Yet some past research shows sick reptiles sometimes do the opposite, moving to colder environments in a response called behavioral hypothermia. Evidence for that remains limited, but it was one of the contrasts that pushed Giacometti's team to look for biological, climatic or pathogen-related explanations in the first place.

Publication details: Danilo Giacometti et al., "When cold-bloods heat up: meta-analytical evidence that climatic variability mediates behavioural fever in amphibians and reptiles," Proceedings of the Royal Society B: Biological Sciences (2026). DOI: 10.1098/rspb.2026.1712.