Environment shapes sleep patterns in a wild nocturnal primate

Abstract

Among primates, the suborder Haplorhini is considered to have evolved a consolidated monophasic sleep pattern, with diurnal species requiring a shorter sleep duration than nocturnal species. Only a few primate species have been systematically studied in their natural habitat where environmental variables, including temperature and light, have a major influence on sleep and activity patterns. Here we report the first sleep study on a nocturnal primate performed in the wild. We fitted seven wild Javan slow lorises ( Nycticebus javanicus ) in West Java, Indonesia with accelerometers that collected activity data, and installed climate loggers in each individual’s home range to collect ambient temperature readings (over 321 days in total). All individuals showed a strictly nocturnal pattern of activity and displayed a striking synchronisation of onset and cessation of activity in relation to sunset and sunrise. The longest consolidated rest episodes were typically clustered near the beginning and towards the end of the light period, and this pattern was inversely related to daily fluctuations of the ambient temperature. The striking relationship between daily activity patterns, light levels and temperature suggests a major role of the environment in shaping the daily architecture of waking and sleep. We concluded that well-known phenotypic variability in daily sleep amount and architecture across species may represent an adaptation to changes in the environment. Our data suggest that the consolidated monophasic sleep patterns shaped by environmental pressures observed in slow lorises represent phylogenetic inertia in the evolution of sleep patterns in humans.

Evidence That Homeostatic Sleep Regulation Depends on Ambient Lighting Conditions during Wakefulness

“…Based on our stringently controlled laboratory data, we have first evidence that homeostatic regulation of human sleep is modulated by prior light exposure levels, which indicates that environmental factors during wakefulness shape human sleep architecture. This goes in line with a recent sleep study performed in a nocturnal primate in the wild, reporting major influences of environmental factors (i.e., light and temperature) on monophasic sleep and activity patterns [22]. In a human field study, Wams et al 2017 [23] found that individuals exposed to higher maximal light intensities experienced larger subsequent SWS accumulation, similarly as reported here.…”

Ecological and social pressures interfere with homeostatic sleep regulation in the wild

“…Although these advances hold great promise for wider application in the future, the invasive nature of polysomnography unfortunately limits its current use to taxa whose daily activities do not interfere with electrodes implanted either subdermally or inter-cranially. Because baboons are highly dexterous and engage in frequent allogrooming, we were unable to apply this gold standard, and instead, resorted to an alternate method in order to ask and answer important questions about the ecology of Jones et al, 2019;Patel et al, 2017;non-human: Bäckman et al, 2017;Davimes et al, 2018;Gravett et al, 2017;Lesku et al, 2011;Malungo et al, 2021;Qin et al, 2020;Reinhardt et al, 2019;Reyes et al, 2021;Samson et al, 2018;Sellers & Crompton, 2004;Sri Kantha & Suzuki, 2006;Suzuki et al, 2018) and marine taxa (Miller et al, 2008;Mitani et al, 2010;Wright et al, 2017) offered a valid alternative to polysomnography. We note that the use of accelerometry can introduce biases in sleep monitoring, typically by overestimating total sleep time as a result of an inability to distinguish resting wakefulness from sleep (Ancoli-Israel et al, 2003;de Souza et al, 2003).…”

Response of Bolivian gray titi monkeys (Plecturocebus donacophilus) to an anthropogenic noise gradient: behavioral and hormonal correlates

“…Whether this noise-related change in the titis' locomotion results from anthropogenic disturbance or is fortuitous (i.e., correlation without causation) remains to be explored. Although little is known about the consequences of sleep deficits in free-ranging nonhuman primates (Reinhardt et al, 2019), one possibility is that nocturnal traffic noise might disrupt sleep patterns, more so in adults than their putative offspring. Adult pairs experiencing sleep disruption near the highway would then compensate with longer or more frequent naps during the day.…”