During torpor in the fat-tailed dwarf lemur, REM sleep has been observed periodically.
The fat-tailed dwarf lemur (Cheirogaleus medius) is native to Madagascar and is unusual among primates because it can hibernate for months. Its torpor usually coincides with Madagascar’s dry season, when food and water are harder to find. Before entering torpor, the lemur stores substantial energy in its tail, which can account for a large share of its body mass.
Researchers found that the lemur periodically enters rapid eye movement, or REM, sleep while torpid. Non-REM sleep, by contrast, has not been observed in these observations. That pattern is especially striking because it differs from findings in hibernating ground squirrels, where non-REM sleep is documented instead.
The lemur’s torpor is also flexible: because Madagascar’s temperatures can remain relatively high, its body temperature may fluctuate with the surrounding tree-hole environment. The species can remain dormant for as long as seven months, making it a remarkable example of hibernation in a tropical primate.