Abstract
Hibernation and short daily torpor are states of energy conservation with reduced metabolism and body temperature. Both hibernation, also called multiday torpor, and daily torpor are common among mammals and occur in at least 11 orders. Within the primates, there is a peculiar situation, because to date torpor has been almost exclusively reported for Malagasy lemurs. The single exception is the African lesser bushbaby, which is capable of daily torpor, but uses it only under extremely adverse conditions. For true hibernation, the geographical restriction was absolute. No primate outside of Madagascar was previously known to hibernate. Since hibernation is commonly viewed as an ancient, plesiomorphic trait, theoretically this could mean that hibernation as an overwintering strategy was lost in all other primates in mainland Africa, Asia, and the Americas. However, we hypothesized that a good candidate species for the use of hibernation, outside of Madagascar should be the pygmy slow loris (Nycticebus pygmaeus), a small primate inhabiting tropical forests. Here, we show that pygmy slow lorises exposed to natural climatic conditions in northern Vietnam during winter indeed undergo torpor lasting up to 63 h, that is, hibernation. Thus, hibernation has been retained in at least one primate outside of Madagascar.
Highlights
All three of these criteria apply to pygmy slow lorises, which are small strepsirrhine primates inhabiting forests in Vietnam, Cambodia, Laos and China with mostly quite seasonal environments
We were able to obtain Tb records from a total of five animals, including three animals recorded during winter. Despite this limited number of individuals, our results leave no doubt that N. pygmaeus has the capability to hibernate, as all animals monitored during winter did undergo bouts of multiday torpor (Fig. 2)
Hibernation is defined by the occurrence of torpor bouts that last longer than 24 hours (e.g.11,12), which clearly is the case in pygmy slow lorises
Summary
All three of these criteria apply to pygmy slow lorises, which are small strepsirrhine primates inhabiting forests in Vietnam, Cambodia, Laos and China with mostly quite seasonal environments. In northern Vietnam, for example, the climate is profoundly seasonal with wet warm summers and cool dry winters during which ambient temperature (Ta) reaches 5 °C8. Given their relatively small body size (~400 g) www.nature.com/scientificreports/. Associated high rates of heat loss, low winter temperatures can be expected to create high energetic costs for thermoregulation in pygmy slow lorises During winter this omnivorous species faces a shortage of fresh vegetation and insects[9]. The animals were kept in large outdoor enclosures, which allowed for both recapture and veterinary surveillance, but were exposed to natural climatic conditions in northern Vietnam
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