Sleep in the rock hyrax, Procavia capensis

Area of Science:

• Zoology
• Sleep Science
• Mammalian Biology

Background:

• The rock hyrax (Procavia capensis) is a social mammal inhabiting Southern Africa.
• Previous assumptions classified the rock hyrax as strictly diurnal.

Purpose of the Study:

• To investigate the sleep patterns of the rock hyrax under controlled conditions.
• To quantify sleep states including waking, slow wave sleep (SWS), rapid eye movement (REM), and a novel state, somnus innominatus (SI).

Main Methods:

• Continuous 72-hour sleep recording of 5 wild-captured rock hyraxes using telemetry.
• Analysis of electroencephalogram (EEG), electromyogram (EMG), and heart rate to define sleep states.

Main Results:

• Rock hyraxes spent 66.2% of their time awake, 25.1% in SWS, 3% in SI, and only 0.4% (less than 6 minutes/day) in unambiguous REM sleep.
• A novel sleep state, somnus innominatus (SI), was identified, potentially representing a form of low-voltage non-REM or a novel REM subdivision.
• The most frequent state transition was wake → SWS → wake.
• No significant differences in sleep duration or episodes were observed between light and dark periods.

Conclusions:

• Rock hyraxes exhibit exceptionally low amounts of REM sleep compared to other terrestrial mammals.
• The identified somnus innominatus (SI) state requires further investigation to determine its classification.
• The study challenges the prior classification of rock hyraxes as strongly diurnal, indicating more complex activity patterns.