Erin L. Sauer, Nadia Trejo, Jason T. Hoverman, and Jason R. Rohr
Pathogens impose strong selective pressures on their hosts, driving the evolution of host behaviours that reduce disease risk. Hosts often change their behaviour in response to pathogen detection to resist and avoid disease. For example, some ectothermic hosts (i.e. ‘cold blooded’ species that cannot regulate their body temperatures independently from environmental temperature) can respond to pathogen exposure by exhibiting a behavioural fever, which is a short-term increase in temperature preference. The ability of wildlife populations to rapidly respond to pathogens using behaviour is critical for reducing the impacts of disease outbreaks. But we have limited information regarding the ability of ectothermic wildlife to resist diseases by altering their behaviour.
We set out to experimentally examine the effect of host behaviour on ranaviral infections, which affect at least 175 species of ectothermic vertebrates. We measured temperature preferences of Southern toads (Anaxyrus terrestris) before and after viral exposure. We found evidence for behavioural fever during the first two days after viral exposure. If heat itself was responsible for slowing viral growth, we would expect to find that reaching a critical temperature was important. But we found that an increase in baseline temperature preference was more important for reducing disease than simply reaching an absolute temperature. Our results suggest that behavioural fever reduces ranaviral infection by increasing immune efficiency and not simply slowing viral growth directly with heat.