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 laboratoryreared 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. Of the approximately 6,400 extant mammalian species 1 , sleep data has been gathered on only about 70 2 , 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). The detailed examination of sleep architecture in other mammalian and non-model species is important to understand the common features and possible functions of sleep, as well as to identify unusual features that some species may have evolved in specific environments 3. In order to make these comparisons between species, the common features of sleep must be noted first. Sleep has been defined with several criteria: rapid reversibility, decreased sensory responsiveness, and species-specific sleep posture 4. This definition extends to all animals that have been determined to have sleep behaviors, not just mammals. Sleep can then be further subdivided using physiological measures. As determined with traditional electroencephalography (EEG) and electromyography (EMG), mammals typically begin sleep with an increase in amplitude and slowing of the EEG, and a decrease in muscle tone 5 as compared to wake, and have two very different kinds of sleep: REM (rapid-eyemovement) and non-REM (NREM). In humans, NREM is separated into various stages (N1, N2, N3), which may or may not exist in other mammals to varying degrees. By completing comparative studies of sleep and circadian rhythms and noting unique phenomena, there are opportunities for determining the physiological basis or adaptive functions of specific sleep or circadian behaviors. To better understand sleep diversity among murid rodents, we aimed to characterize sleep and wake in A. cahirinus, a ...
