Social thermoregulation and torpor in the Siberian hamster

Abstract

SUMMARYSocial thermoregulation and huddling bring about energy benefits to animals sharing a nest because of the smaller surface-tovolume ratio of a huddle and the higher local temperature in the nest. We tested whether living in groups and huddling affect daily torpor, metabolic rate and seasonal changes in the body mass of a small heterothermic rodent, the Siberian hamster (Phodopus sungorus), housed under semi-natural conditions both singly and in groups of four litter-mates. We predicted that in hamsters housed in groups: (1) synchronized torpor bouts would be longer and deeper than non-synchronized ones but shallower than in solitary hamsters, (2) seasonal variations in metabolic rate would be lower than in solitary hamsters, and (3) the winter decrease in body mass would be smaller in grouped than in singly housed hamsters. We found that group housing led to a smaller decrease in body mass in winter, and affected the length and depth of daily torpor. In group-living hamsters more than 50% of all torpor episodes were synchronized and torpid animals were often found in huddles formed of all cage-mates. The longest and deepest torpor bouts in groups were recorded when all animals in a group entered torpor simultaneously. Although the minimum body temperature during torpor was higher, torpor duration was slightly longer than in solitary hamsters. We did not record significant differences in the body mass-adjusted rate of oxygen consumption between solitary and grouped animals, either in the cold or at the lower critical temperature. We conclude that social thermoregulation enables maintenance of a larger body mass, and thus a larger body fat content, which can ensure better body condition at the beginning of the reproductive season.

Aerobic power, huddling and the efficiency of torpor in the South American marsupial, Dromiciops gliroides

“…Also known as social thermoregulation (Arnold, 1993; Jefimow et al, 2011), huddling represents up to 53% of energy saving during cold, both in birds and mammals (Gilbert et al, 2010). However, how huddling interacts with other energy saving strategies such as torpor (Frey, 1991; Namekata and Geiser, 2009; Jefimow et al, 2011) has been little studied.…”

Is cold acclimation of benefit to hibernating rodents?

“…Given the high consumption of oxygen required for thermogenesis (Chi and Wang, 2011), this may account for the progressive, regional rewarming noted for the hamster (Osborne et al, 2005). Furthermore, this may in part explain the 'social thermoregulation' previously noted for the Siberian hamster (Jefimow et al, 2011), as grouped animals show narrower ranges of core temperatures during torpor, which may prevent a catastrophic fall in core temperature beyond which cardiovascular control is inadequate. CA may represent an indefinite period of preservation prior to committing to a wholesale transcriptome remodelling during hibernation.…”

Basking hamsters reduce resting metabolism, body temperature and energy costs during rewarming from torpor

“…Hamsters were held in a ventilated room at the Research Institute of Wildlife Ecology under a natural photoperiod from summer (16 h:8 h light: dark) to winter (9.5 h:14.5 h light:dark; sunrise ∼07:00 h, sunset ∼17:15 h) in February when most measurements were performed and torpor is regularly expressed (Jefimow et al, 2011). Pelage colour of the animals was at stage 4, i.e.…”