Optional strategies for reduced metabolism in gray mouse lemurs
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Among the order of primates, torpor has been described only for the small Malagasy cheirogaleids Microcebus and Cheirogaleus. The nocturnal, gray mouse lemur, Microcebus murinus (approx. 60 g), is capable of entering into and spontaneously arousing from apparently daily torpor during the dry season in response to reduced temperatures and low food and water sources. Mark–recapture studies indicated that this primate species might also hibernate for several weeks, although physiological evidence is lacking. In the present study, we investigated patterns of body temperature in two free-ranging M. murinus during the austral winter using temperature-sensitive data loggers implanted subdermally. One lemur hibernated and remained inactive for 4 weeks. During this time, body temperature followed the ambient temperature passively with a minimum body temperature of 11.5°C, interrupted by irregular arousals to normothermic levels. Under the same conditions, the second individual displayed only short bouts of torpor in the early morning hours but maintained stable normothermic body temperatures throughout its nocturnal activity. Reduction of body temperature was less pronounced in the mouse lemur that utilized short bouts of torpor with a minimum value of 27°C. Despite the small sample size, our findings provide the first physiological confirmation that free-ranging individuals of M. murinus from the humid evergreen littoral rain forest have the option to utilize short torpor bouts or hibernation under the same conditions as two alternative energy-conserving physiological solutions to environmental constraints.
KeywordsMicrocebus murinus Daily torpor Hibernation Body temperature
We thank the Direction des Eaux et Forêts and the Commission Tripartite for their authorization to carry out this work. The study has been conducted within the framework of biodiversity assessment studies of the littoral forest fragments initiated by QIT Madagascar Minerals (QMM). J.-B. Ramanamanjato, M. Vincelette, and their environmental and conservation team of QMM provided excellent support in the field. This paper is part of the Accord de Collaboration between the Université d'Anananarivo (Départements de Biologie Animale and d'Anthropologie et Biologie Evolutive), QMM, and Hamburg University. Financial support from the German Research Foundation (SCHM 1391/2-1, 2-3, 2-4) is gratefully acknowledged. We declare that the experiments complied with the current laws in Madagascar (N° 101—DGDRF/SCB).
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