Abstract
Most published sleep studies use three species: human, house mouse, or Norway rat. The degree to which data from these species captures variability in mammalian sleep remains unclear. To gain insight into mammalian sleep diversity, we examined sleep architecture in the spiny basal murid rodent Acomys cahirinus. First, we used a piezoelectric system validated for Mus musculus to monitor sleep in both species. We also included wild M. musculus to control for alterations generated by laboratory-reared conditions for M. musculus. Using this comparative framework, we found that A. cahirinus, lab M. musculus, and wild M. musculus were primarily nocturnal, but exhibited distinct behavioral patterns. Although the activity of A. cahirinus increased sharply at dark onset, it decreased sharply just two hours later under group and individual housing conditions. To further characterize sleep patterns and sleep-related variables, we set up EEG/EMG and video recordings and found that A. cahirinus sleep significantly more than M. musculus, exhibit nearly three times more REM, and sleep almost exclusively with their eyes open. The observed differences in A. cahirinus sleep architecture raise questions about the evolutionary drivers of sleep behavior.
Highlights
Most published sleep studies use three species: human, house mouse, or Norway rat
Field observations, trapping studies, and laboratory investigations suggest that A. russatus may have evolved flexible sleep patterns and a higher tolerance for heat and aridity than A. cahirinus10–13
A. cahirinus showed a sharp increase in activity at dark onset, which is common in nocturnal species, but exhibited an unusual sharp decrease in activity just two hours later (Fig. 1A, B)
Summary
Most published sleep studies use three species: human, house mouse, or Norway rat. The degree to which data from these species captures variability in mammalian sleep remains unclear. Of the approximately 6,400 extant mammalian species, sleep data has been gathered on only about 702, leaving many unknowns about the variation of mammalian sleep Of these 70 species, sleep has been detailed extensively only in three (with thousands of publications each): humans, house mice (Mus musculus), and Norway rat (Rattus norvegicus). Competitive interaction may have contributed to evolutionary changes in circadian rhythms and sleep behaviors of both Acomys species14 These results may reflect the adaptive value and a stronger role of a food-entrainable oscillator in A. cahirinus due to the shift in activity that corresponds to shifted foraging times. They responded with phase adjustments to light exposure as seen in other nocturnal species These studies measured waking activity, but did not investigate sleep behavior of A. cahirinus or any other spiny mouse species. To provide a detailed characterization of sleep architecture we used various methodologies: [1] a non-invasive piezoelectric system, [2] EEG/EMG, and [3] infrared (IR) cameras
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