New study discovers the impact of environment on sleep patterns in wild primates which could help to understand human sleep

Friday, 12 July 2019

Slow loris in sleep posture

The first-ever sleep study on a nocturnal primate performed in the wild has provided fascinating insights which might tell us more about our own sleep patterns.

Published in Scientific Reports, the article entitled Environment shapes sleep patterns in a wild nocturnal primate was led by Oxford Brookes University‘s Kathleen Reinhardt, under the remit of Professor Anna Nekaris’ Little Fireface Project in West Java, Indonesia. The study was conducted in association with colleagues at the University of Oxford and the University of Oslo.

The research suggests that being able to sleep in one continuous block has been shaped by environmental pressures observed in slow lorises. This finding could help in understanding the evolutionary impact on sleep patterns in humans.

The team of researchers fitted wild Javan slow lorises (Nycticebus javanicus) with devices that recorded movement to assess their waking and sleeping patterns, alongside recording ambient temperature and light phases.

Sleep and circadian rhythms are traditionally studied in stable laboratory conditions, which allow for the control for numerous extrinsic factors, but typically do not take into account the influence of natural environmental factors on sleep patterns.

This is the first-ever systematic sleep study in a nocturnal primate performed in the wild. It is based on monitoring of activity and rest in slow lorises throughout the day in their natural habitat. The researchers not only provide a detailed account of the daily pattern of sleep in this species in the wild, but also highlight the crucial importance of the environment in shaping sleep in a natural setting.

These data unequivocally suggest that sleep patterns are particularly sensitive to the light levels and ambient temperature, shaping the overall pattern of activity and rest across a 24 hour period.

Kathleen Reinhardt from Oxford Brookes University’s Nocturnal Primate Research Group in the Faculty of Humanities and Social Sciences, said “Arguing from the evolutionary viewpoint, sleep evolved not only as a process that dealt with immediate biological responses, but also as a response to environmental conditions. Thus the well-known flexibility in sleep patterns that we can visually see between species, reflects the fact that it evolved together with species adapting to their habitats.”

The specific characteristics of sleep reflect its numerous functions for brain and body physiology, which collectively overweigh risks associated with sleep, ensuring the fitness of species.

Co-author, Dr. Vladyslav Vyazovskiy at the University of Oxford’s Department of Physiology, Anatomy and Genetics adds, "Only a few animal species were studied both in captivity and in their natural habitat, and the knowledge of how animals sleep in the wild is insufficient. This is particularly important because in the natural environment the need to sleep must be balanced against environmental pressures and other homeostatic needs, which may be very different from laboratory conditions. Our study therefore raises an intriguing question of how wild animals cope with obtaining sufficient sleep, or compensate for sleep loss incurred during spontaneous or enforced wakefulness while adjusting their sleep pattern to predictable and unpredictable fluctuations in the environment." 

This study therefore fills an important gap in our knowledge of sleep in primates including humans and helps to bridge the gap between laboratory-based studies with those in natural environments. This notion is further emphasised by Co-author Dr. R. Adriana Hernandez-Aguilar, from the University of Oslo: “In the last decade, several sleep studies have been performed on indigenous human populations in South America and Africa. These studies provided novel fundamental insights into sleep evolution in humans, but also the claims made sparked debates in the scientific community. More work needs to be done on wild primates to better understand the evolution of human sleep. Thus, our study is especially timely and relevant, as it focuses on a wild primate.”

Professor Anna Nekaris added, “The Javan slow loris is Critically Endangered, and the studied population occurs in an area with extensive noisy human activity. The ability for lorises to maintain such a fixed sleep pattern under these conditions points to their incredible adaptability. Furthermore, the use of logging devices that hang from their collars a bit like a dog tag, shows that we can get important data from non-invasive methods.” 

Kathleen Reinhardt concluded: “Studying sleep in the wild is essential to further our understanding of sleep ecology, physiology and evolution. Specifically, our results challenge the assumption that monophasic sleep of a shorter duration evolved in the monkeys and apes and suggest that human sleep patterns have a longer evolutionary history than previously believed.”

You can find out more about research, teaching and primate conversation work at Oxford Brookes on the University’s website.