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25 June 2004 (All day)
Hibernation isn't just for winter creatures. Researchers have identified the first example of a tropical mammal that undergoes prolonged hibernation.
Among primates, the fat-tailed lemur of Madagascar takes top prize for laziness, hiding itself away in tree holes and snoozing through 7 months of the year. This behavior, discovered by a team led by Kathrin Dausmann, an animal physiologist at Philipps University in Marburg, Germany, seemed suspiciously like hibernation, although no tropical mammal--and certainly no primate--has ever been known to hibernate. The strategy has been thought to be used only by arctic and temperate mammals for surviving harsh winters. But Madagascar is sweltering most of the year.
The team reports in the 23 June issue of Nature how they observed individual fat-tailed lemurs for weeks at a time, tracking their body temperature with implanted radio-transmitting thermometers. They also recorded the temperature of their tree holes. Just like squirrels hibernating their way through winter, the fat-tailed lemurs shut down internal heat generation, Dausmann's team found. But unlike winter hibernators, these lemurs have to warm up periodically to at least 30oC, making the choice of tree hole important. Those who snuggled up in a well-insulated hole in a thick tree where the temperature remained stable below 30oC had to rouse themselves about once a week, spending extra energy to heat up and stay warm for 6 hours. But the lemurs who chose a tiny tree hole in a slim tree let the hot Madagascar days do the job for them, never needing to generate their own heat or wake up. Lemurs from well-insulated holes switched to drafty, thin-walled tree holes when they found them, but never the other way 'round. Dausmann suspects that the advantage of hibernating may be to get through the 8-month dry season when food becomes harder to find.
The study lends support to a long-standing theory that the first mammal colonizers of Madagascar could have survived the long ocean journey with the help of hibernation, says Anne Yoder, a biologist at Yale University. However, she is surprised by fat-tailed lemurs' preference for drafty sleeping quarters, adding that "no one would have predicted that."