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Research article - Peer-reviewed, 2022

Seasonality in Biological Rhythms in Scandinavian brown Bears

Thiel, Alexandra; Giroud, Sylvain; Hertel, Anne G.; Friebe, Andrea; Devineau, Olivier; Fuchs, Boris; Blanc, Stephane; Stoen, Ole-Gunnar; Laske, Timothy G.; Arnemo, Jon M.; Evans, Alina L.

Abstract

Biological rhythms, such as rhythms in activity and body temperature, are usually highly synchronized and entrained by environmental conditions, such as photoperiod. However, how the expression of these rhythms changes during hibernation, when the perception of environmental cues is limited, has not yet been fully understood for all hibernators, especially in the wild. The brown bear (Ursus arctos) in Scandinavia lives in a highly seasonal environment and adapts to harsh winter conditions by exhibiting hibernation, characterized by reduced metabolism and activity. In this study, we aimed to explore the expression of biological rhythms in activity, body temperature and heart rate of free-ranging brown bears over the annual cycle, including active, hibernation and the transition states around den entry and exit. We found that rhythms in physiology and activity are mostly synchronized and entrained by the light-dark cycle during the bears' active state with predominantly diel and ultradian rhythms for body temperature, activity and heart rate. However, during hibernation, rhythms in body temperature and heart rate were considerably slowed down to infradian rhythms, influenced by the amount of snow in the denning area, whereas rhythms in activity remained diel. Rhythms in the transition states when bears prepared for entering or coming out of hibernation state displayed a combination of infradian and diel rhythms, indicating the preparation of the body for the change in environmental conditions. These results reveal that brown bears adjust their biological rhythms to the seasonal environment they inhabit. Rhythms in physiology and activity show simultaneity during the active state but are partly disconnected from each other during hibernation, when bears are most sheltered from the environment.

Keywords

Brown bear (Ursus arctos); body temperature; circadian rhythm; heart rate; hibernation; lomb-scargle periodogram; multiday rhythms; activity

Published in

Frontiers in Physiology
2022, volume: 13, article number: 785706
Publisher: FRONTIERS MEDIA SA

Authors' information

Thiel, Alexandra
Inland Norway University of Applied Sciences
Giroud, Sylvain
University of Veterinary Medicine Vienna
Hertel, Anne G.
Ludwig Maximilian University Munich (LMU)
Friebe, Andrea
Norwegian Institute Nature Research
Devineau, Olivier
Inland Norway University of Applied Sciences
Fuchs, Boris
Inland Norway University of Applied Sciences
Blanc, Stephane
Universites de Strasbourg Etablissements Associes
Støen, Ole‑Gunnar
Norwegian Institute for Nature Research (NINA)
Laske, Timothy G.
University of Minnesota
Arnemo, Jon M. (Arnemo, Jon)
Inland Norway University of Applied Sciences
Swedish University of Agricultural Sciences, Department of Wildlife, Fish and Environmental Studies
Evans, Alina L.
Inland Norway University of Applied Sciences

UKÄ Subject classification

Zoology

Publication Identifiers

DOI: https://doi.org/10.3389/fphys.2022.785706

URI (permanent link to this page)

https://res.slu.se/id/publ/117355