Bears hibernate during winters. So do some bats, squirrels, and many other mammals. But very few primates are known to hibernate. In fact, scientists have previously observed hibernation in only three species of lemurs, all found in Madagascar: the western fat-tailed lemur, Crossley’s dwarf lemur and Sibree’s dwarf lemur.

Now, researchers have discovered a non-Malagasy primate species — the pygmy slow loris (Nycticebus pygmaeus) inhabiting forests of southeast Asia — that hibernates during winter. This is the first record of a hibernating primate outside of Madagascar, according to a new study published in Nature’s Scientific Reports.

“There had been anecdotal observations of pygmy lorises that remained inactive for several days,” Thomas Ruf of Universty of Veterinary Medicine, Vienna, Austria, said in a statement. “Occasionally animals were encountered that felt cool to the touch. However, we discovered only now that the lorises actually hibernate.”

By lowering body temperature and slowing down metabolism, hibernating animals try to conserve energy during cold winters when food is not readily available. The tiny nocturnal pygmy slow loris too, faces shortage of fresh vegetation and insects when ambient temperatures dip.

To see if these animals actually hibernate during winter, Ruf and his colleagues recorded body temperature of five pygmy slow lorises in fall, winter and spring in a Vietnamese primate reserve.

In the reserve, the researchers kept the animals in large, outdoor enclosures, “which allowed for both recapture and veterinary surveillance,” the authors write, while exposing the animals to “natural climatic conditions in northern Vietnam.”

The team found that between December and February, all five lorises showed bouts of inactivity (or torpor) lasting multiple days, interspersed with periods of shorter torpor and normal body temperature. Both male and female pygmy slow lorises would hibernate up to 63 hours at a time, the researchers found.

Moreover, the study found that hibernation in the five lorises was restricted to the coldest months.

The researchers write that despite the limited number of individuals in the study, the results “leave no doubt that N. pygmaeus has the capability to hibernate, as all animals (of both sexes) monitored during winter did undergo bouts of multiday torpor.”

According to the researchers, hibernation in the pygmy slow lorises is likely due to an internal annual clock that induces hibernation in response to reducing food supply, possibly triggered by decreasing ambient temperature.

“In Vietnam, where we studied the animals, there are pronounced seasons,” Ruf said in the statement. “Ambient temperature can drop to 5 centigrade. This is exactly when the probability of animals entering a hibernation episode was highest.”

Scientists had previously believed that specific environmental conditions or evolutionary histories in Madagascar may have limited hibernating primates to the island. However, the discovery of hibernation in pygmy slow lorises occurring in southeast Asia opens up the possibility of finding other non-Malagasy primates that hibernate.

“Our new finding of a hibernating primate species outside Madagascar sheds new light on the evolution of hibernation”, Ruf said. “Possibly, hibernation as an overwintering strategy was lost in other primates in Africa, Asia, and the Americas. However, perhaps hibernation is also used by further primate species, which have not been studied yet.”

Citation:

• Ruf T, Streicher U, Stalder G.L, Nadler T. and Walzer C (2015) Hibernation in the pygmy slow loris (Nycticebus pygmaeus): multiday torpor in primates is not restricted to Madagascar. Scientific Reports. DOI: 10.1038/SREP17392

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Shreya Dasgupta Editor

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