Scientists have discovered that two tiny, clawless, tree-living lemur species hibernate. Underground. For up to six months a year. Given that the furry animals are primates, the findings have exciting implications for possible human hibernation.
From chipmunks to bats to even turtles, numerous wild species hibernate. By slowing their metabolism, breath rate and heart rate, these animals can put themselves into a state of suspended animation, allowing them to go without food or water (or bathroom breaks) for months on end.
Almost a decade ago scientists learned that the fat-tailed dwarf lemur (Cheirogaleus medius) of western Madagascar hibernates — it's the first primate and the first topical mammal discovered to do so. Interestingly, the lemur's seasonal torpor has nothing to do with cold weather.
You see, the lemurs live in dry deciduous forests that have fluctuating temperatures throughout the year. Rather than being constantly cold, winter is actually marked by heightened temperature oscillations (up to 30 degrees C a day) and a scarcity of food. So the primates spend about 5 months gorging on food, then they find a comfy tree hole and knock out for the next 7 months, using the fat reserves in their tails to survive.
For most mammals, hibernation is accompanied by stable low body temperatures. Every once in a while, for reasons still not completely understood, the animal will arouse and its temperature will shoot up to normal levels for 12 to 24 hours. Oddly, some of the fat-tailed dwarf lemurs don't have go through these energetically expensive periods of arousal — if they choose a poorly insulated tree hole, their body temperatures naturally rise with the weather.
"That was pretty much all we knew about primate hibernation," says Marina Blanco, a biological anthropologist at Duke University in North Carolina. But Blanco and her colleagues wondered if other Madagascar lemur species also hibernate. In particular, do any of the species on the eastern side of the island, where the environment is very different, also hibernate?
A Crossley’s dwarf lemur up in a tree in the Tsinjoarivo forest. Courtesy of Kathrin Dausmann.
The team decided to study two species of dwarf lemur species — Sibree’s dwarf lemur (C. sibreei) and Crossley’s dwarf lemur (C. crossleyi) — in Tsinjoarivo, a high-altitude forest in central and eastern Madagascar. Unlike the home of the western lemur, "the eastern forest is pretty cold and its temperature can go down significantly during the dry season," Blanco told io9.
To see how the easterners were getting along during the chilly dry season, the team fitted the primates with radio collars that could measure skin temperature. They found that the lemurs did, in fact, hibernate. But unlike their western relatives, the lemurs in Tsinjoarivo only hibernated for 3 to 6 months, though the researchers aren't yet sure why.
"It's something we are trying to figure out," Blanco says. "We're thinking that it has something to do with how much fat they can accumulate."
Instead of nestling inside of trees, the eastern lemurs choose to hibernate buried under a spongy layer of root, humus and leaf matter in small underground burrows, no more than 15 inches deep. Each lemur keeps its own burrow, but family members often hibernate in close proximity to one another. The burrowing behavior is particularly odd considering that the squirrel-sized primates live up in the trees throughout the rest of the year.
"Just let me sleep, damn you!" — hibernating lemur. Courtesy of Jean Ranaivoarisoa.
The clawless lemurs may ditch the trees so they don't freeze to death during winter, Blanco notes, adding that the ground burrows are highly insulated. And since the eastern lemurs are protected from the outside environment, they are able to maintain the typical low body temperature seen in hibernating mammals (which also means that they go through those weird periodic arousals). The team suggests that maintaining a stable body temperature may be the "default" hibernating strategy, and that the western lemurs would also bury themselves if they didn't have to deal with hard, dry soils.
The new discovery may eventually help scientists figure out how to induce hibernation in people. "There is a lot of research into that topic," Blanco says. Currently, there are scientists who are looking at what's going on physiologically during hibernation, while other researchers are focusing on the gene expression of the behavior. "Because the lemurs are primates, our biology is more similar to them than to squirrels, so hopefully we will be able to find similar genes and processes that could help us hibernate," she says.
The short-term goal, then, is to figure out how to induce a safe state of hypothermia, mimicking the low body temperatures the eastern lemurs maintain in hibernation — this would help people stay in suspended conditions for a while, Blanco says. And if scientists can isolate all of the components necessary for primate hibernation, we may be able to turn people into hibernators. Naturally, this has huge implications for long-distance space travel, where people would likely need to enter a dormant state to survive the long trips. "It's all very exciting for many people," she says.
The discovery is described in the journal Scientific Reports.
Top image via Marina Blanco.