Correlates and consequences of heterothermy in mammals

Endotherms are capable of using internal heat to precisely regulate body temperature at an elevated level, yet there is considerable variation in the range of body temperatures (heterothermy) expressed by an endotherm. In this thesis, I exploit two different approaches to address the causes and consequences of heterothermy in mammals, reflective of an underlying trade-off between the functional benefits and energetic costs of endothermy. I first conduct an inter-specific, empirical analysis of mammalian body temperatures reported in the literature, treating heterothermy as a continuous variable spanning all endotherms, to examine factors that predict the degree of body temperature fluctuation observed in different species. Across mammals, body temperature variation decreased with body mass and increased with proximity to the poles, and food hoarders were less heterothermic than non-hoarders. Further, with these allometric, latitudinal, and behavioural effects included, phylogeny still had a strong influence on the degree of body temperature variation in a given species. In my second chapter, I examine potential behavioural consequences of torpor, a special case of heterothermy involving a pronounced reduction in body temperature and metabolism. This research was conducted in captivity on eastern chipmunks (Tamias striatus), which exhibit deep torpor and show extreme individual variation in heterothermy that spans most of the heterothermic continuum expressed by mammals in general. To test the hypothesis that torpor impairs exploration and spatial memory, individual performance was assessed in an open field and a radial arm maze prior to and during hibernation. Results showed that habituation in the open field was negatively impacted by torpor, particularly prolonged torpor, however performance in the radial maze, tested later in the arousal period, was less affected. Thus, torpor expression clearly affects behaviour, but these effects are very transient and therefore unlikely to have long-term fitness consequences. Mammals overall are characterized by extensive variability, both among and within species, in the degree of body temperature variation, with species occupying cold climates and relying on ephemeral food being characterized by the most heterothermy. As to why more individuals and species do not exploit the energetic savings of high-amplitude heterothermy, captive research suggests the immediate costs of reduced body temperature on endotherm function may be more important than its long-term effects.

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.