Individual variation of daily torpor and body mass change during winter in the large Japanese field mouse (Apodemus speciosus)
Daily torpor is a strategy used by some overwintering small endotherms to aid in energy conservation. However, the pattern of torpor varies among individuals within species and populations, even under the same environmental conditions, with significant implications for survival rate and reproductive success. Body mass is one factor that may influence this variation, especially in some small mammals that accumulate fat stores prior to overwintering. However, to our knowledge there has been no previous study examining the detailed relationships between torpor expression and body mass change in small mammals that hoard food as an energy resource during winter. The large Japanese field mouse, Apodemus speciosus, whose winter survival strategy depends on food caches instead of fat stores, displays daily torpor under artificial winter conditions (short-day photoperiod and cold). The present study clarifies the characteristics and patterns of daily torpor and body mass change in this species in the laboratory. Although expression of daily torpor was facilitated progressively as in other species, the observed patterns of torpor expression and body mass change showed considerable individual variation. Moreover, there was no obvious correlation between body mass and daily torpor expression. Therefore, it is suggested that in A. speciosus body mass may not contribute to individual variation of daily torpor during winter. Daily torpor during winter may be adjusted by not only mechanisms common to other small mammals, but also species-specific factors relating to the external or internal reserves of energy in small mammals.
KeywordsApodemus speciosus Body mass Body temperature Daily torpor Individual variation Winter adaptation
We would like to thank Mr. Ryousuke Ozaki for help with field research, and Ms. Ayano Oka and Mr. Rintaroh Hayashi for their help with animal maintenance. We also thank anonymous reviewers for their constructive comments.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All animal procedures were approved by the Animal Experimentation Committee of the University of Miyazaki (Permission Nos. 2005-053 and 2012-002).
- Dikic D, Heldmaier G, Meyer CW (2008) Induced torpor in different strains of laboratory mice. In: Lovegrove BG, McKechnie AE (eds) Hypometabolism in animals: hibernation, torpor and cryobiology. University of KwaZulu-Natal, Pietermaritzburg, pp 223–230Google Scholar
- Goldman BD, Darrow JM, Duncan MJ, Yogev L (1986) Photoperiod, reproductive hormones, and winter torpor in three hamster species. In: Heller HC, Musacchia XJ, Wang LCH (eds) Living in the cold: physiological and biochemical adaptations. Elsevier, New York, pp 341–350Google Scholar
- Gummer DL (2005) Geographic variation in torpor patterns: the northernmost prairie dogs and kangaroo rats. Dissertation, University of Saskatchewan, SaskatoonGoogle Scholar
- Heldmaier G (1989) Seasonal acclimatization of energy requirements in mammals: functional significance of body weight control, hypothermia, torpor and hibernation. In: Wieser W, Gnaiger E (eds) Energy transformations in cells and organisms. Georg Thieme Verlag, Stuttgart, pp 130–139Google Scholar
- Imaizumi Y (1979) Seed storing behavior of Apodemus speciosus and Apodemus argenteus. Zool Mag 88:43–49Google Scholar
- Nakata K, Saitoh T, Iwasa MA (2009) Apodemus speciosus (Temminck, 1844). In: Ohdachi SD, Ishibashi Y, Iwasa MA, Saitoh T (eds) The wild mammals of Japan. Shoukadoh, Kyoto, pp 169–171Google Scholar
- Oh HS, Mōri T (1998) Growth, development and reproduction in captive of the large Japanese field mouse, Apodemus speciosus (Rodentia, Muridae). J Fac Agr Kyushu Univ 43:397–408Google Scholar
- Pinheiro J, Bates D, DebRoy S, Sarkar D, R Development Core Team (2012) nlme: linear and nonlinear mixed effects models. R package version 3:1–103Google Scholar
- R Core Team (2016) R: a language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. http://www.R-project.org/
- Sakai Y, Sakamoto SH, Kato GA, Iwamoto N, Ozaki R, Eto T, Shinohara A, Morita T, Koshimoto C (2013) Rearing method to induce natural mating of large Japanese field mouse, Apodemus speciosus. Honyuruikagaku [Mammalian Science] 53:57–65 (in Japanese with English abstract) Google Scholar
- Sekijima T (1995) Metabolic rates of two congeneric woodmice, Apodemus argenteus and A. speciosus (Rodentia: Muridae), in Japan. J Mamm Soc Japan 20:143–149Google Scholar
- Takada Y (1993) Body fat of mice, Apodemus speciosus, Mus musculus and Micromys minutus. Honyurui Kagaku (Mammalian Science) 32:107–115 (in Japanese with English abstract) Google Scholar