Huddling is more important than rest site selection for thermoregulation in southern bamboo lemurs

Abstract

Resting site selection can have important effects on the behaviour and fitness of organisms. The maintenance of optimal body temperatures (Tb) when faced with environmental variables has often been attributed to either specific microhabitat rest site characteristics or to behavioural strategies. Among many small group living endotherms, social thermoregulation (i.e., huddling) is utilised as a behavioural energy conservation mechanism at low ambient temperatures (Ta), thus decreasing the metabolic cost of maintaining Tb. Though unusual among primates, lemurs are hypometabolic and exhibit a diversity of thermoregulatory strategies; however, objective Tb measurements have thus far been limited to small-bodied lemurs (e.g., Cheirogaleids). As such, we sought to determine whether a medium-sized lemur model, the southern bamboo lemur (Hapalemur meridionalis), would maintain thermoregulation through microhabitat rest site selection, huddling behaviour, or potentially both strategies. Within a degraded littoral forest fragment in southeast Madagascar, we conducted full-day focal observations on three groups of H. meridionalis between January and December 2013. Adult individuals were collared with data-loggers that collected instantaneous skin temperature Tsk (°C). We calculated the mean Tsk of the focal individual during each resting bout, and the proportional rate of huddling between the focal and conspecifics. In addition, we recorded all resting sites utilised ≥15 min and collected standard tree characteristics. We fitted Linear Mixed-Effects Models to determine the thermoregulatory combined effect of specific resting site characteristics, huddling behaviour, and environmental variables on Tsk. Our results showed that lemurs selected tree sites with larger diameter at breast height; however, huddling was most predictive of increasing Tsk whereas resting site characteristics were not included in the bestfit model. It is possible that microhabitat rest site selection is not significant in a degraded Behavioural thermoregulation in Hapalemur 3 forest as the potential environmental buffering is limited, thus thermoregulatory mechanisms are likely best served by behavioural strategies, i.e., social huddling.

Modelling the emergence of rodent filial huddling from physiological huddling

“…Other rodents, including mice [ 5 ], rats [ 6 ], rabbits [ 7 ] and degus [ 8 ], huddle to insulate from the cold, by collectively reducing the exposed surface-area-to-volume ratio of the group [ 9 , 10 ]. And social thermoregulation in primates (bamboo lemurs) has recently been shown to be more important for temperature homeostasis than the choice of resting site [ 11 ].…”

Sleep patterns, daytime predation, and the evolution of diurnal sleep site selection in lorisiforms

“…The requirement for thermoregulation may also explain why the smaller species of lorisiform such as Loris, Galago, Galagoides, Paragalago and Sciurocheirus (which lose heat more quickly than their larger relatives) tend to sleep together, thereby sharing body heat (Nowack, Wippich, Mzilikazi, & Dausmann, ; cf. Eppley, Watzek, Dausmann, Ganzhorn, & Donati, ). Some of these smaller taxa, including Pg.…”

Energy (Im-)Balance in Frugivorous Lemurs in Southern Madagascar: A Preliminary Study in Lemur catta and Eulemur rufifrons × collaris

“…In Microcebus murinus, for example, TEE does not differ between the dry and the wet seasons in normothermic individuals [Schmid and Speakman, 2000]. Other studies have shown that gregarious lemurs reduce thermal stress by using behavioral thermoregulation like social huddles and peculiar resting postures and, according to some authors, by performing daylight and nocturnal activity [Donati et al, 2011;LaFleur et al, 2014;Kelley et al, 2016;Eppley et al, 2017;but see Fletcher et al, 2012].…”