Hibernating Primates Found In Southeast Asia

Vietnamese pygmy slow lorises join the lemurs of Madagascar as the only primates known to hibernate.

AsianScientist (Dec. 9, 2015) – The first hibernating primate to be found outside of Madagascar has been found: the pygmy slow loris (Nycticebus pygmaeus). The discovery was made by a team at the Research Institute of Wildlife Ecology (RIWE) at the Vetmeduni Vienna, collaborating with colleagues from the Vietnamese Endangered Primate Rescue Center.

Hibernation is a state of energy conservation during which body temperature and metabolism are drastically reduced for over 24 hours. Shorter periods are called daily torpor.

While many mammals hibernate, previously the only known primate hibernators were three species of lemurs. Lemurs exclusively live on the island of Madagascar, where they hibernate during the dry season, mainly to conserve water.

The pygmy slow loris belong to the so-called wet nosed primates, reach a body size of about 20 centimeter and a body mass of 400 gram. They live in Southeast Asia and are nocturnal, tree-living animals.

The researchers investigated the body temperatures of five pygmy lorises in fall, winter, and spring in a Vietnamese primate reservation. It turned out that both sexes repeatedly showed hibernation episodes lasting up to 63 hours between December and February.

According to first author Associate Professor Thomas Ruf of the RIWE, the underlying reason is likely an endogenous annual clock, which induces hibernation at a time of the year when food abundance is decreasing. However, it is also the decreasing ambient temperature that triggers hibernation.

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

According to Ruf, free living pygmy lorises are adapted to reduced food availability in winter. During the cold season food is sparse. Hibernation then helps to save energy.

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

Previously, scientists had assumed that the environmental conditions on Madagascar may have been crucial for the occurrence of hibernation among primates.

“Our new finding of a hibernating primate species outside Madagascar sheds new light on the evolution of hibernation”, emphasized Ruf. “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.”

The article can be found at: Ruf et al. (2015) Hibernation in the Pygmy Slow Loris (Nycticebus pygmaeus): Multiday Torpor in Primates is not Restricted to Madagascar.

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Source: University of Veterinary Medicine Vienna.
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