for National Geographic News
Madagascar, a large, tropical island off the east coast of Africa, isn't the kind of place you'd expect to find a mammal that hibernates. Yet researchers say a small, nocturnal lemur resorts to the same tactic used by bears, squirrels, and dormice to survive cold northern wintersspending at least seven months of the year hibernating through harsh times brought on by drought.
The German-based team say their study is the only report of prolonged hibernation in a tropical mammal. Furthermore, writing in this week's scientific journal Nature, they claim the study provides the first proof of hibernation in any species of primate.
The study focused on the fat-tailed dwarf lemur (Cheirogaleus medius), one of a group of snout-faced primates for which Madagascar is famous. The island boasts some 32 lemur species, the highest percentage of indigenous primates anywhere on Earth.
The fat-tail dwarf lemur gorges on fruit, flowers, and insects during a short rainy season between December and February. As its body weight increases by around 40 percent, the lemur's tail swells massively with stored fat reserves. The animal, which usually weighs five ounces (150 grams), then goes into a torpor, marked by reduced activity and appetite.
Scientists previously noted that this cycle of behavior is most pronounced in western Madagascar, where the climate veers between extremes. Here the "fat-tail" was found to take to holes in tree trunks during prolonged periods of drought, when trees shed their leaves and food becomes scarce.
Led by scientists from Phillips University's animal physiology department in Marburg, Germany, the team revealed that the fat-tail's body temperature varied to an extent previously unknown in mammals. Daily fluctuations ranged almost 20 degrees Celsius (nearly 40 degrees Fahrenheit), with temperatures recorded from as low as 9.3 degrees Celsius (48.7 degrees Fahrenheit) to well over 30 degrees Celsius (86 degrees Fahrenheit).
Body temperatures were found to correlate closely with how well each tree hole was insulated. The researchers say this suggests the lemurs body temperatures are regulated by external conditions, as with lizards and other reptiles, instead of being maintained internally.
"They follow changes in environmental temperature as if they were a piece of stone," said Gerhard Heldmaier, from Phillips University. This, he says, is potentially of great benefit, as it helps fat-tails conserve their fat reserves.
For reasons not fully understood, most hibernating mammals usually go through periods of arousal, when they bring their body temperatures up to normal levels. "This costs them a lot of energy," said Heldmaier. He added that the lemurs studied experienced body temperatures as high as 35.9 degrees C (97 degrees F) and didnt need to go through arousal during hibernation.
The researchers say the condition of hibernation should no longer be seen as synonymous with low body temperatures, as is presently the case.
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