Wider daily temperature ranges linked to stronger fevers in amphibians and reptiles

When amphibians and reptiles fall ill, they sometimes raise their body temperature above their normal level by moving to a warmer area. This behavior, known as behavioral fever, was the focus of a recent study conducted by researchers at the University of São Paulo and São Paulo State University. The scientists reviewed 47 previous studies to better understand why some infected amphibians and reptiles exhibit larger fever responses than others.

Their findings, published in Proceedings of the Royal Society B: Biological Sciences, revealed that animals living in regions with greater day–night temperature fluctuations tend to have stronger fever responses. Additionally, they found clearer evidence of fever in amphibians compared to reptiles. Danilo Giacometti, the paper's first author, expressed his motivation for the research, stating that after completing his Ph.D. in Canada, he wanted to return to Brazil to study how immune challenges impact the thermal biology of amphibians and reptiles.

The researchers compiled data from 47 earlier studies, which involved 49 different species. They analyzed whether larger day–night temperature swings at collection sites were associated with greater changes in body temperature after infection. The researchers noted that species that have evolved in variable climates often demonstrate a greater ability to utilize thermal resources through behavioral thermoregulation.

However, they also pointed out a key difference between amphibians and reptiles in terms of thermal biology. Amphibians have thin skin that is more susceptible to dehydration under warming conditions. To explore the factors influencing the behavior of sick animals, the researchers compared the body temperatures of healthy individuals with those of infected or challenged animals of the same species.

They also accounted for similarities among closely related species. Prior research has suggested that the physiological mechanisms underlying fever are relatively conserved across various animals, including invertebrates and vertebrates. Studies on lizards had previously demonstrated that the ability to seek warmer temperatures (behavioral fever) can provide adaptive benefits in combating infections and potentially conferring immunity.

Surprisingly, the team's findings indicated stronger evidence of behavioral fever in amphibians compared to reptiles, despite the expectation that amphibians would be less inclined to seek warmer temperatures due to the risk of dehydration. The researchers hypothesized that amphibians might avoid raising their body temperatures when infected to prevent dehydration.

Their analysis also revealed that bacterial challenges were associated with more conclusive evidence of behavioral fever compared to fungal or viral challenges. Notably, their study did not examine whether behavioral fever enhances survival chances after infection. The researchers concluded that preserving thermal heterogeneity is crucial, as animals capable of exploring diverse thermal resources may be better equipped to handle immune challenges compared to those living in thermally stable environments.