Abstract
As ecosystems undergo global changes, there is an increasing interest on understanding how organisms respond to changing environments. In the tropics, climate change results in more extreme events. The induced food shortage may impact the energetic trade- off between metabolic demands. We tested with a food restriction experiment, how captive Grey Mouse Lemurs (Microcebus murinus) modify torpor-based energy savings in response to contrasted regimes of food availability, and to an immune challenge. Twelve individuals were fed ad libitum, and 12 were exposed to a 40% caloric restriction during 11 weeks. Afterwards, six of each group were exposed to a 2-week 80% caloric restriction. Two weeks later, six individuals per group (ALI and CRI) received a challenge that activates both innate and acquired immunity. Energetic modulations were characterised by changes in daily torpor (body temperature). Results. Daily torpor was increased by chronic caloric restric- tion, with a relatively small effect of acute restriction. All immune-challenged individuals exhibited a pyrogenic response, and skipped diurnal torpor. The pyrogenic response was stronger in CRI than in ALI, but CRI individuals returned more rapidly to deep torpor than ALI individuals. During ‘bad’ years and extreme events, individuals would increase the amount of energy savings by increasing the length and the depth of torpor. When exposed to a pathogen, the acute response of under- nourished individuals would be energetically constrained. Our results suggest that facultative, heterothermic organisms may overcome climate-driven, sudden changes in food availability by modulating their energy savings. However, this may have an immune cost.
Published Version
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