A first for mammals: Tropical hibernating

Madagascan fat-tailed dwarf lemurs hibernate during the winter, even though daily temperatures often top 30°C (86°F).

The lemurs (Cheirogaleus medius) are the first tropical mammals, and the first primates, found to hibernate, Kathrin H. Dausmann of Phillips University in Marburg, Germany, and her colleagues report in the June 24 Nature. The animals appear to exploit their tropical conditions to hibernate with an energy-saving strategy not seen before in hibernators.

Dausmann and her colleagues monitored 53 animals fitted with temperature-sensitive radio collars. The researchers found that the lemurs hibernate from April to October, the dry season in Madagascar’s winter.

Most of the lemurs settled into relatively thin-walled tree cavities where the inside air temperature regularly rose above 30°C. In this circumstance, the animals’ body temperatures followed their shelters’ air temperatures, often changing some 20°C during a day.

The researchers saw no sign that these animals revved up their own metabolisms while hibernating. This was a surprise, because all other mammals known to hibernate rely on metabolic spikes to periodically raise their body temperatures. Just why these other hibernators take the energetically expensive step of briefly pushing their temperatures up to normal every week or two remains unknown, says Dausmann.

Some lemurs hibernated in thicker trees that didn’t heat up as much as outside air did. These animals periodically turned on their metabolic engines to bump up their body temperatures beyond 30°C. Five lemurs in trees with very thick, well-insulated walls spent most of their time snoozing with body temperatures near 20°C, but on a weekly basis made an intense metabolic effort to top the 30°C mark. When the same lemur hibernates in trees with more or less insulation, its body-heating pattern changes, say the researchers.

Dausmann adds that she suspects that other tropical mammals also hibernate and use the same heating strategy.