Abstract
Energy expenditure during winter can be reduced by expressing torpor, which is characterized by decreased metabolic rate and body temperature. In addition to deep, multiday torpor bouts alternating with short arousal episodes during the hibernation period, common hamsters can also enter shallow torpor bouts (STBs), lasting for less than 24 h at a minimum body temperature between 30-20 °C. Food supplements provided shortly before winter have been shown to shorten hibernation in males, but did not affect hibernation duration in females. In the presented study, we analyzed the expression of STBs and compared supplemented to unsupplemented common hamsters. Body temperature during winter was recorded using subcutaneously implanted data loggers (iButtons). The results revealed that supplemented males showed more STBs and thus spent more time in shallow torpor than unsupplemented individuals. The duration of STBs, however, was shorter in supplemented males and both mean and minimum body temperature were significantly higher compared to unsupplemented males. In females, shallow torpor expression did not differ between individuals with and without food supplements. STBs were mainly expressed before the onset of the first deep, multiday torpor bout, but the number of STBs was not related to that of deep torpor bouts. These results indicate that in males, shallow torpor combined with feeding on food stores could be the more appropriate overwintering strategy when sufficient external energy reserves are available. Females generally cache more food than males and are therefore assumed to be less affected by the additional food stores. These results underline the flexibility of the species in the use of heterothermy and could enable adequate and rapid responses to changes in food availability.
Highlights
Several bird and mammalian species have the capability to escape unfavorable environmental conditions by saving energy via reducing metabolic rate and body temperature during so-called torpor bouts
The results of the presented study showed that this extended euthermic period was frequently interrupted by shallow torpor bouts (STBs) as this type of torpor was primarily expressed before the individuals entered the first deep torpor bout
Shallow torpor bouts prior to hibernation onset have been documented in some hibernating species and were traditionally thought to be preparatory to deep torpor (Strumwasser, 1958), but more recent studies demonstrated that shallow torpor is not necessary to enter hibernation (e.g., Sheriff et al, 2012) and can be expressed even year-round (Wilz and Heldmaier, 2000)
Summary
Several bird and mammalian species have the capability to escape unfavorable environmental conditions by saving energy via reducing metabolic rate and body temperature during so-called torpor bouts. In addition to typical deep torpor bouts, common hamsters are known to regularly express short and shallow torpor (Wollnik and Schmidt, 1995; Wassmer and Wollnik, 1997; Siutz and Millesi, 2017; Siutz et al, 2017), which is characterized by less pronounced drops in body temperature (with minimum values ranging between 30 and 20◦C) and a duration shorter than 24 h. Hamsters kept under laboratory conditions were found to enter shallow torpor primarily in the morning hours, which was significantly later compared to entry into deep torpor. This daily rhythm of torpor entrance, was not found under semi-natural conditions, i.e., without exposure to light-dark cycles (Wassmer and Wollnik, 1997; Wassmer, 1998), indicating that shallow torpor expressed by hamsters is functionally distinct from daily torpor
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.