Experimental evidence for behavioural cooling as a response to virus infection in an ectothermic vertebrate

Behavioural plasticity may contribute to the ability of wild animals to survive disease outbreaks. In absence of endogen heat control, ectothermic animals adjust their body temperature behaviourally. While many studies reported behavioural fever, its opposite, behavioural cooling-when infected animals lower their body temperature by using cool microenvironments-remains poorly documented.

Here, we report the first experimental evidence of behavioural cooling in an ectothermic vertebrate as a response to pathogenic infection. We investigated thermoregulatory responses in tadpoles of the agile frog Rana dalmatina, a cool-adapted amphibian, following experimental infection with a ranavirus that can replicate well at high temperatures. Tadpoles were placed either in thermal gradients or homogeneously cool environments for 5 days post-exposure. In thermal gradients, all tadpoles reduced their preferred temperatures over time, but this decrease was steeper in infected tadpoles, and individuals with higher infection intensities preferred cooler temperatures. Infected tadpoles decreased the range of their preferred body temperatures over time, while a similar trend was not detectable in non-infected tadpoles. Infection prevalence was similar between the two thermal environments, yet infection intensities were significantly higher in the thermal gradient.

These results suggest fine-tuned thermoregulation by infected tadpoles to balance out the benefits of behavioural cooling for fighting a pathogen versus the immune-suppressive and developmental costs of low temperatures.