The Lemur Underground: New Evidence for Primate Hibernation
From bears slumbering through the winter in their dens to frogs sinking into muddy tombs of suspended animation, a wide spectrum of animals resort to hibernation to survive until spring. Just a mention of hibernation conjures images of snow-blanketed forests and ice-covered ponds, with animals hiding out from barren, dormant wintry landscapes.
A group of small tropical primates is breaking the trend, however—recent research demonstrates that several dwarf lemurs in Madagascar undergo seasonal hibernation periods for up to eight months of the year. While it had previously been known that the western fat-tailed dwarf lemur (Cheirogaleus medius) spends seven months of the year hibernating in tree holes (Dausmann et al. 2004), until recently there was no evidence for any other primate undertaking significant hibernation periods.
A recent paper in Nature’s open access journal, Scientific Reports, however, presents brand-new evidence of hibernation in two other species, the Sibree’s dwarf lemur (C. sibreei) and the Crossley’s dwarf lemur (C. crossleyi; sometimes called the furry-eared dwarf lemur), both of which occur in east-central Madagascar’s high altitude forests (Blanco et al. 2013). While it may not seem as though primates would need to hibernate on a tropical island, Madagascar’s mountainous regions can indeed experience temperatures that dip below freezing—a significant thermoregulatory challenge for a squirrel-sized primate. Thus, a group of researchers from the University of Hamburg, the University of Antananarivo, and Duke University decided to see if the overwintering strategies of eastern dwarf lemurs resembled that of the western species.
The researchers managed to trap dwarf lemurs prior to hibernation season, and outfitted each animal with a collar that featured both a radio transmitter and a temperature sensor. The collars allowed the animals to be located after they had retreated to their hibernacula, in addition to tracking fluctuations in body temperature while the lemurs were hibernating.
The results were surprising and fascinating. Not only do these tropical lemurs hibernate for 3-6 months out of the year, the arboreal primates actually spend their hibernation underground, despite their lack of adaptations for a fossorial lifestyle. The lemurs nestled 10-40 cm beneath a the forest’s floor of secondary roots and humus, no small feat for an animal that gives every appearance of a life optimized for the treetops. Each lemur denned up alone, and they used just one or two hibernacula sites per season.
This underground hibernation habit is extremely interesting; the other lemur species known to hibernate, C. medius, uses tree hollows exclusively. The researchers suggest that this difference in hibernation sites could be partially due to constraints imposed by soil type: soil in C. medius’ habitat is hard and dry, unlike the soft soils of the eastern forests. Another significance of the findings about hibernacula choice is that the eastern species use tree hollows for their normal resting periods during the non-hibernation season, meaning that hibernation is an event with a very specific site selection pattern, rather than just an extended rest in their usual shelters.
Temperature data from the collars showed that C. sibreei and C. crossleyi tend to keep their body temperatures more stable while hibernating than does C. medius, which may highlight another advantage of subterranean hibernation. Soil provides more resistance to ambient temperature fluctuations than hollow trees, meaning that the eastern species are better insulated during their long rest than their western relative.
A final noteworthy aspect of this study is that C. sibreei and C. crossleyi are basal species within their branch of the lemur phylogeny. This raises the question of whether their hibernation patterns may be an ancestral condition for dwarf lemurs. Further studies on other species and populations will provide further insights into just how widespread these behaviors are among upland lemur species, in addition to yielding discoveries about how these small tropical mammals have adapted their metabolic physiology to achieve such long stretches of dormancy.
Blanco, M., Dausmann, K., Ranaivoarisoa, J., & Yoder, A. (2013). Underground hibernation in a primate Scientific Reports, 3 DOI: 10.1038/srep01768
Dausmann, K.H., Glos, J., Ganzhorn, J.U., Heldmaier, G. (2004). Hibernation in a tropical primate. Nature 429, 825-826.