title: Huddling facilitates expression of daily torpor in the large Japanese field mouse Apodemus speciosus.
abstract: Small endotherms employ multiple adaptations to maintain energy balance in winter, including spontaneous daily torpor and simultaneous huddling. The relationships between these adaptations have been discussed in several previous studies, but it has not been well-established if huddling actually affects the expression of torpor in small endotherms. We examine whether and how huddling affects the expression of torpor in the large Japanese field mouse Apodemus speciosus, which is known to become torpid under artificial winter conditions. The mice were found to adjust expression of torpor in response to the number of cage mates. Torpor frequency and minimum torpid body temperature were both significantly elevated when the number of cage mates was increased, but there was no significant change in torpor bout length. Rewarming rate on arousal was lower when the number of cage mates was increased, suggesting reduction in endogenous rewarming due to exogenous passive rewarming. Food consumption per mouse decreased significantly with increasing number of cage mates. Thus, our study demonstrates that social thermoregulatory behaviors such as huddling can facilitate expression of spontaneous daily torpor in small rodents. These findings suggest that energy constraints, such as ambient temperature and food availability may not be the only modulating factors on the expression of daily torpor.
authors.affiliation: Interdisciplinary Graduate School of Agriculture and Engineering, Kibana Campus, University of Miyazaki, Miyazaki 889-2192, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Eto
authors.affiliation: Division of Bio-Resources, Frontier Science Research Center, Kiyotake Campus, University of Miyazaki, Miyazaki 889-1692, Japan.
authors.forename: Shinsuke H
authors.initials: SH
authors.lastname: Sakamoto
authors.affiliation: Interdisciplinary Graduate School of Agriculture and Engineering, Kibana Campus, University of Miyazaki, Miyazaki 889-2192, Japan.
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Okubo
authors.affiliation: Division of Bio-Resources, Frontier Science Research Center, Kiyotake Campus, University of Miyazaki, Miyazaki 889-1692, Japan.
authors.forename: Chihiro
authors.initials: C
authors.lastname: Koshimoto
authors.affiliation: Faculty of Agriculture, Kibana Campus, University of Miyazaki, Miyazaki 889-2192, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kashimura
authors.affiliation: Faculty of Agriculture, Kibana Campus, University of Miyazaki, Miyazaki 889-2192, Japan. Electronic address: morita@cc.miyazaki-u.ac.jp.
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Morita
mesh_terms: D000064:Acclimatization / Q000502:physiology; D000818:Animals; D001833:Body Temperature Regulation / Q000502:physiology*; D004435:Eating; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D008297:Male; D051379:Mice; D012737:Sex Factors; D013997:Time Factors; D064348:Torpor / Q000502:physiology*
keywords: Apodemus speciosus; Daily torpor; Huddling; Small endotherm; Social thermoregulation; Winter adaptation