Short and hyperthermic torpor responses in the Malagasy bat Macronycteris commersoni reveal a broader hypometabolic scope in heterotherms
The energy budgets of animal species are closely linked to their ecology, and balancing energy expenditure with energy acquisition is key for survival. Changes in animals’ environments can be challenging, particularly for bats, which are small endotherms with large uninsulated flight membranes. Heterothermy is a powerful response used to cope with changing environmental conditions. Recent research has revealed that many tropical and subtropical species are heterothermic and display torpor with patterns unlike those of “classical” heterotherms from temperate and arctic regions. However, only a handful of studies investigating torpor in bats in their natural environment exist. Therefore, we investigated whether the Malagasy bat Macronycteris commersoni enters torpor in the driest and least predictable region in Madagascar. We examined the energy balance and thermal biology of M. commersoni in the field by relating metabolic rate (MR) and skin temperature (Tskin) measurements to local environmental characteristics in the dry and rainy seasons. Macronycteris commersoni entered torpor and showed extreme variability in torpor patterns, including surprisingly short torpor bouts, lasting on average 20 min, interrupted by MR peaks. Torpid MR was remarkably low (0.13 ml O2 h−1 g−1), even when Tskin exceeded that of normothermia (41 °C). Macronycteris commersoni is thus physiologically capable of (1) entering torpor at high ambient temperature and Tskin and (2) rapidly alternating between torpid and normothermic MR resulting in very short bouts. This suggests that the scope of hypometabolism amongst heterothermic animals is broader than previously assumed and underlines the importance of further investigation into the torpor continuum.
KeywordsEnergy budgets Thermoregulation Torpor Seasonality Chiroptera Madagascar
This study has been conducted under the “Accord de Collaboration” between the Université d’Antananarivo (Département de Biologie Animale), Madagascar National Parks and the University of Hamburg. We thank these authorities and the Ministère de l’Environnement, de l’Ecologie et des Forêts for project authorization and support. We also thank J. Ganzhorn for allowing us to operate and use the facilities from research Camp Andranovao and Marie Schoroth as well as our field assistants for their constant support in the field. In addition, J. Rakotondranary and Y. R. Ratovonamana helped with the organization of logistics, fieldwork and authorizations. The research was approved by the Directeur du Système des Aires Protégées, Ministère de l’Environnement, Antananarivo (Autorisation de recherche no. 90/16/MEEMF/SG/DGF/DAPT/SCBT.Re and 003/17/MEEF/SG/DGF/DSAP/SCB.Re, Direction Générale des Forêts) and all described procedures comply with the current laws of Madagascar.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.
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