Another primate "sleeps" away hard times

Hibernation allows an organism to lower its metabolism, heart rate, body temperature, and breathing in order to expend less energy during what may be a difficult time, such as a cold winter.  Hibernation is a tactic commonly associated with rodents and polar bears but primates do it too. The fat-tailed dwarf lemur (Cheirogaleus medius) on the island of Madagascar hibernates during the dry season, using the fat in its tail to survive the winter. The Crossley's dwarf lemur (Cheirogaleus crossleyi) and the Sibree's dwarf lemur (Cheirogaleus sibreei) also hibernate. Some primates (Microcebus murinus, Allocebus trichotis, Galago moholi, and others) will enter what is called torpor, during which body temperature and metabolism is lowered but for a period less than 24 hours. Lemurs were thought to be the only primate that hibernated, until a close cousin changed the game.

Pygmy slow loris. Photo: David Haring at Duke Lemur Center

It has recently been reported that the pygmy slow loris (Nycticebus pygmaeus), a nocturnal primate living in Cambodia, China, Laos, and Vietnam does in fact hibernate (Ruf et al., 2015). The authors behind this study set out to find a hibernating primate outside of Madagascar and they succeeded.

Ruf and colleagues found it hard to believe that hibernation in primates would be restricted to only Madagascar, so they started thinking about what environmental conditions and physical characteristics would make an animal likely to hibernate. They hypothesized that a hibernating primate would be small, as most hibernating animals are (Ruf and Geiser, 2015), that the animal would live in an environment that is distinctly seasonal in temperatures and/or precipitation, and in an environment with seasonal changes in food availability. Given the primates known to use torpor, primates falling into the suborder Strepsirrhines seemed like their best bet.

The pygmy slow loris fit their criteria. It was logical that a small primate facing cold temperatures in winter and low food availability would adapt using hibernation. Thus lowering energy requirements during a period of limited resources. While previous descriptions of the pygmy slow loris were in accord with hibernation (Ratajszczak, 1998; Streicher, 2005), no measurements had been taken. Thus, Ruf and colleagues decided to take some.

After measuring temperature (but not metabolic rate) in five adults over 769 days total, animals hibernated for several days during midwinter interspersed with periods of activity and or torpor. On average, animals hibernated for 43 hours (± 3 hours with a range of 25.9-62.6 hours).

Thus, evolutionary mechanisms have not limited hibernation in primates to Madagascar. As more research is done, it is possible that hibernation will be found in other primate species inhabiting seasonal environments.

Links of possible interest:
Discovery of hibernation in fat-tailed dwarf lemur
Primate hibernation more common than previously thought
The costs and benefits of hibernation

Sources:

Ratajszczak, R. (1998). Taxonomy, distribution and status of the lesser slow loris Nycticebus pygmaeus and their implications for captive management. Folia Primatologica, 69(Suppl. 1), 171-174.

Ruf, T., Streicher, U., Stalder, G. L., Nadler, T., & Walzer, C. (2015). Hibernation in the pygmy slow loris (Nycticebus pygmaeus): multiday torpor in primates is not restricted to Madagascar. Scientific reports, 5.

Ruf, T. & Geiser, F. Daily torpor and hibernation in birds and mammals. Biol. Rev. 90, 891–926, doi: 10.1111/brv.12137 (2015).

Streicher, U. (2005). Seasonal body weight changes in pygmy lorises Nycticebus pygmaeus. Verhandlungsber. Zootierkrk, 42, 144-145.