Body temperature changes during simulated bacterial infection in a songbird: fever at night and hypothermia at day

Abstract

Although fever (a closely regulated increase in body temperature in response to infection) typically is beneficial, it is energetically costly and may induce detrimentally high body temperatures. This can increase the susceptibility to energetic bottlenecks and risks of overheating in some organisms. Accordingly, it could be particularly interesting to study fever in small birds, which have comparatively high metabolic rates and high, variable body temperatures. We therefore investigated two aspects of fever and other sickness behaviours (circadian variation, dose-dependence) in a small songbird, the zebra finch. We injected lipopolysaccharide (LPS) at the beginning of the day and night, respectively, and subsequently monitored body temperature, body mass change and food intake for the duration of the response. We found pronounced circadian variation in body temperature response to LPS-injection, manifested by (dose-dependent) hypothermia at day but fever at night. This resulted in body temperature during the peak response being relatively similar at day and at night. Day-to-night differences might be explained in the context of circadian variation in body temperature: songbirds have a high daytime body temperature that is augmented by substantial heat production peaks during activity. This might require a trade-off between the benefit of fever and the risk of overheating. In contrast, at night when body temperature is typically lower and less variable, fever can be used to mitigate infection. We suggest that the change in body temperature during infection in small songbirds is context-dependent and regulated to promote survival according to individual demands at the time of infection.