title: Magnitude of food overabundance affects expression of daily torpor.
abstract: Many small mammal species use torpor as a strategy for reducing energy expenditure in winter. Some rodent hibernators also hoard food to provide reserves of energy, and individuals with large hoards express less torpor than those with smaller reserves. These facts imply that animals can recognize levels of food availability, but where food is very plentiful, it is unclear whether torpor expression is affected by temporal changes in the extent of food overabundance. Moreover, the relationship between daily torpor and excess food availability has not been clearly established. The large Japanese field mouse Apodemus speciosus caches food for use as a winter energy resource and exhibits daily torpor under artificial winter conditions. The present study examined whether individuals exposed to different magnitudes of overabundant food exhibited differences in expression of daily torpor, and secondly whether torpor expression varied in response to changes in the overall quantity of overabundant food. It was observed that while absolute quantities of overabundant food did not appear to affect daily torpor expression, the mice did respond to changes in food availability, even when food remained overabundant. This suggests that the mice respond to fluctuations in food availability, even where these changes do not place any constraint on energy budgets. Thus recognition of changing food availability cannot be a purely physiological response to shortage or plenty, and may contribute to predictions of future energy availability. The expression of torpor was inhibited in response to increasing food availability, and the mice used shallower torpor when food availability increased to superabundance. These findings suggest that daily torpor may be regulated not only physiologically in response to energy constraints but also psychologically, via recognition of food availability.
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: Faculty of Agriculture, Kibana Campus, University of Miyazaki, Miyazaki 889-2192, Japan.
authors.forename: Rintaroh
authors.initials: R
authors.lastname: Hayashi
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: Faculty of Agriculture, Kibana Campus, University of Miyazaki, Miyazaki 889-2192, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kashimura
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: Division of Bio-Resources, Frontier Science Research Center, Kiyotake Campus, University of Miyazaki, Miyazaki 889-1692, Japan. Electronic address: aposhin1@med.miyazaki-u.ac.jp.
authors.forename: Shinsuke H
authors.initials: SH
authors.lastname: Sakamoto
authors.affiliation: Faculty of Agriculture, Kibana Campus, University of Miyazaki, Miyazaki 889-2192, Japan.
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Morita
mesh_terms: D000818:Animals; D049628:Body Size; D005260:Female; D005502:Food; D008297:Male; D051189:Murinae / Q000502:physiology* / Q000523:psychology*; D013997:Time Factors; D064348:Torpor
keywords: Apodemus speciosus; Body temperature; Daily torpor; Food overabundance; Recognition; Small mammal