Reversal of the adipostat control of torpor during migration in hummingbirds
Abstract
Many small endotherms use torpor to reduce metabolic rate and manage daily energy balance. However, the physiological 'rules' that govern torpor use are unclear. We tracked torpor use and body composition in ruby-throated hummingbirds (Archilochus colubris), a long-distance migrant, throughout the summer using respirometry and quantitative magnetic resonance. During the mid-summer, birds entered torpor at consistently low fat stores (~5% of body mass), and torpor duration was negatively related to evening fat load. Remarkably, this energy-emergency strategy was abandoned in the late summer when birds accumulated fat for migration. During the migration period, birds were more likely to enter torpor on nights when they had higher fat stores, and fat gain was positively correlated with the amount of torpor used. These findings demonstrate the versatility of torpor throughout the annual cycle and suggest a fundamental change in physiological feedback between adiposity and torpor during migration. Moreover, this study highlights the underappreciated importance of facultative heterothermy in migratory ecology.
Data availability
All data is available in the main text or the supplementary materials. Analyses reported in this article can be reproduced using the data and code provided by Eberts et al., (2021).
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Data from: Reversal of the adipostat control of torpor during migration in hummingbirdsDryad Digital Repository, doi:10.5061/dryad.p8cz8w9qg.
Article and author information
Author details
Funding
Natural Sciences and Engineering Research Council of Canada (06129-2015 RGPIN)
- Kenneth C Welch Jr
Human Frontier Science Program (RGP0062/2016)
- Kenneth C Welch Jr
Natural Sciences and Engineering Research Council of Canada Discovery Grant (05245-2015 RGPIN)
- Christopher G Guglielmo
Canada Foundation for Innovation, Ontario Research Fund
- Christopher G Guglielmo
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Ethics
Animal experimentation: Details of animal husbandry and all experiments were approved by the University of Toronto (protocol # 20011649) and the University of Western Ontario Animal Care Committees (protocol #2018-092). Hummingbirds were captured under Ontario Collecting Permit SC-00041.
Copyright
© 2021, Eberts et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Further reading
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