Abstract
The rock hyrax, Procavia capensis, is a highly social, diurnal mammal. In the current study several physiologically measurable parameters of sleep, as well as the accompanying behavior, were recorded continuously from five rock hyraxes, for 72 h under solitary (experimental animal alone in the recording chamber), and social conditions (experimental animal with 1 or 2 additional, non-implanted animals in the recording chamber). The results revealed no significant differences between solitary and social conditions for total sleep times, number of episodes, episode duration or slow wave activity (SWA) for all states examined. The only significant difference observed between social and solitary conditions was the average duration of rapid eye movement (REM) sleep episodes. REM sleep episode duration was on average 20 s and 40 s longer under social conditions daily and during the dark period, respectively. It is hypothesized that the increase in REM sleep episode duration under social conditions could possibly be attributed to improved thermoregulation strategies, however considering the limited sample size and design of the current study further investigations are needed to confirm this finding. Whether the conclusions and the observations made in this study can be generalized to all naturally socially sleeping mammals remains an open question.
Highlights
Sleep is a homeostatically regulated process and it is characterized by its easy reversibility, immobility and reduced responsiveness to sensory stimuli
The aim of the present study was to investigate the effect of sociality on sleep architecture in a naturally occurring social, diurnal species, the rock hyrax
It has been hypothesized that social species sleep less, have more fragmented sleep and lower non rapid eye movement sleep (NREM) and rapid eye movement (REM) sleep quotas (Capellini et al, 2008a,b, 2009)
Summary
Sleep is a homeostatically regulated process and it is characterized by its easy reversibility, immobility and reduced responsiveness to sensory stimuli. In addition to the classic mammalian sleep states an additional state, unique to the rock hyrax, termed somnus innominatus (meaning sleep without a name, SI) has been identified. It is currently not known if SI is form of low-voltage SWS or REM sleep as it is characterized by a low-voltage, high frequency electroencephalogram (EEG), an electromyogram (EMG) that is similar in amplitude to the preceding SWS episode and a mostly regular heart rate (see Gravett et al, 2012)
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