Why do dwarf lemurs live so long—and can humans, too?
By Peter Klopfer, Ph.D., Co-founder of the Duke Lemur Center and Professor Emeritus of Biology at Duke University. Originally published on pages 14-15 of LEMURS Magazine: The “Why” Issue in February 2024.
When fat-tailed dwarf lemurs enter hibernation at temperatures below 25°C, they show little or no brain activity other than occasional muscle movement. However, at intervals of three to ten days (depending on the temperature), they raise their body temperature to around 30°C for a few hours. During this time, they sleep. These periods of sleep include frequent and lengthy bouts of REM sleep, which in humans are associated with dreams. And these bouts were more frequent and lengthy than at other times, as if the animals had a pent up need to make up for lost opportunities to sleep.
While the act of producing REM waves is not likely to be costly calorically, the rise in body temperature that precedes it, is, and we could measure that cost precisely by monitoring oxygen uptake. It appears that the arousals from torpor account for most of the energy expended during hibernation. Evidently, sleep, from an evolutionary viewpoint, is indeed vitally important.
Do lemurs dream? We still don’t know, although the presence of REM suggests that they do. And since the bulk of the energy expended during hibernation is used to warm up so as to allow these arousal intervals, sleep must indeed have been vital in evolutionary history, as it is today.
We still don’t know why we sleep, but what these lemurs have taught us reinforces the belief that coming to understand the function of sleep is not of trivial significance. Nor is this all there is to this tale of lemur hibernation. Cheirogaleus medius is about squirrel size, 150-250 grams in weight. Mammals of that size generally have a short life span, only two or three years. The European dormouse, which is of similar size and also hibernates for half of each year, is exceptional in that it can live three to four times that long. Associated with this longevity is the observation by a group of Austrian biologists that they regenerate their telomeres after each hibernation season. Telomeres are the codons that serve as the bookends on the DNA strands that comprise the chromosomes. Normally, they shorten with age or trauma and serve as indicators of lifespan.
Since our little dwarf lemurs can live for well over 20 years, we decided to duplicate the dormouse study. This work is still in a preliminary stage, but our early data do suggest that for dwarf lemurs as for dormice (Glis glis), hibernation may be an elixir of life in more than one respect. And since researchers at the Duke Lemur Center have also established that the major genes activated for hibernation are shared by humans, a tantalizing prospect emerges: Can we hope to induce torpor in humans? What inestimable benefits for medical practices, or perhaps even for space travel! Certainly a rich prospect for science fiction. Dwarf lemurs are for real, however, and studying them an ever-growing adventure.
Is hibernation an elixir of life? Jonas, the world’s oldest known fat-tailed dwarf lemur (pictured left), lived at the DLC and died just months shy of his 30th birthday. Non-hibernating mammals of similar size have much shorter life spans of just two to three years.