Huddling Conserves Energy, Decreases Core Body Temperature, but Increases Activity in Brandt's Voles (Lasiopodomys brandtii)

Abstract

Huddling as social thermoregulatory behavior is commonly used by small mammals to reduce heat loss and energy expenditure in the cold. Our study aimed to determine the effect of huddling behavior on energy conservation, thermogenesis, core body temperature (Tb) regulation and body composition in Brandt's voles (Lasiopodomys brandtii). Adult captive-bred female Brandt's voles (n = 124) (~50 g) in 31 cages with 4 individuals each were exposed to cool (23 ± 1°C) and cold (4 ± 1°C) ambient temperatures (Ta) and were allowed to huddle or were physically separated. The cold huddling (Cold-H) groups significantly reduced food intake by 29% and saved digestible energy 156.99 kJ/day compared with cold separated groups (Cold-S); in cool huddling groups (Cool-H) the reduction in food intake was 26% and digestible energy was saved by 105.19 kJ/day in comparison to the separated groups (Cool-S). Resting metabolic rate (RMR) of huddling groups was 35.7 and 37.2% lower than in separated groups at cold and cool Tas, respectively. Maximum non-shivering thermogenesis (NSTmax) of huddling voles was not affected by Ta, but in Cold-S voles it was significantly increased in comparison to Cool-S. Huddling groups decreased wet thermal conductance by 39% compared with separated groups in the cold, but not in the cool Ta. Unexpectedly, huddling voles significantly decreased Tb by 0.25 – 0.50°C at each Ta. Nevertheless, activity of Cold-H voles was higher than in Cold-S voles. Thus, huddling is energetically highly effective because of reduced metabolic rate, thermogenic capacity and relaxed Tb regulation despite the increase of activity. Therefore, Brandt's voles can remain active and maintain their body condition without increased energetic costs during cold exposure. This study highlights the ecological significance of huddling behavior for maintenance of individual fitness at low costs, and thus survival of population during severe winter in small mammals.

Rapid establishment of teat order and allonursing in wild boar (Sus scrofa)

“…Indeed, avoiding heat loss seems to be of particular importance in wild boar as piglets are known to be vulnerable to low ambient temperatures (Briedermann, ). Further, both wild boar and domestic piglets have been reported to huddle extensively (Gundlach, ), which facilitates the reduction of heat loss (Gilbert, McCafferty, Giroud, Ancel, & Blanc, ; Sukhchuluun, Zhang, Chi, & Wang, ). This is supported by our observations that the piglets were mostly lying closely together in one farrowing box while sleeping, especially when ambient temperatures were below 0°C (anecdotal observation by LA).…”

Huddling relieves myocardial glycogen synthesis of Brandt’s voles in mild cold environment

“…Voles in the cool separated groups (CS) were housed individually in cages, whereas voles in the cool huddling groups (CH) were housed together in a cage (two males and two females). Group size (four voles in each cage) ensured most animals remained inactive in a huddle (Sukhchuluun et al, 2018). The temperature in the cabinet was set to 15°C and the light regime was as same as the CON group.…”

“…All animals were anaesthetized with 50 mg kg -1 sodium pentobarbital between 08:00 and 11:00 on the last day of the experimental period [19,30]. After the rapid removal of cardiac muscle, portions of the ventricles were immediately cut off and fixed in glutaraldehyde.…”

“…It is a cooperative group behavior, permitting individuals involved in social thermoregulation to minimize heat loss and thereby lower energy expenditure, possibly allowing reallocation of saved energy to other functions [1,18]. It is commonly exhibited in small mammals and birds to reduce heat and energy loss under cold environments [19][20][21][22]. Research has shown that many mammals, such as degu (Octodon degus), Damaraland mole-rat (Cryptomys damarensis), and Natal mole-rat (C. hottentotus natalensis), huddle when the ambient temperature is lower than 15-20°C, with an energy saving of up to 30% [23,24].…”

“…Studies have shown that mild cooling can significantly change the level of oxidative stress in the cardiac muscle of Brandt's voles [29]. Furthermore, their metabolic rate and thermogenic capacity decrease but activity increases compared with separated individuals under low temperatures, suggesting that huddling is a good strategy for small mammals to cope with cold environments [19]. Glycogen is one of the most important energy supply substances in muscles.…”