The adaptive significance of sleep: Testing the immune theory in a natural primate population – SLEEP

The functional significance and the physiological mechanisms of sleep remain unsolved. A largely untested assumption is that sleep evolved to sustain immune defences and protect against diseases. The relationship between sleep and the immune system is of prime scientific and medical interests because a sharp decline in the average duration and quality of sleep has been documented over recent decades in all human populations. The relationship between sleep and the immune system have been, however, investigated almost exclusively under abnormal experimental conditions. Yet, understanding the functional significance of sleep variation within and between subjects requires studies in the natural ecological conditions in which sleep has evolved. Such observational and experimental studies have never been performed in large, natural populations of vertebrates.
In this project, we propose to study the mechanistic and functional relationships between sleep and the immune system using long-term individual monitoring of nonhuman primates in combination with field experiments and laboratory analyses. In particular, we propose to identify i) the different factors causing sleep variation within and across individuals; ii) the mechanistic, physiological and immunological pathways that relate sleep to immunity and conversely; and iii) the short- and long-term consequences of both chronic and acute lack of sleep on animal physiology, behaviour and fitness. We propose to attain these three objectives in two populations of mandrills (Mandrillus sphinx) showing contrasted lifestyles and different constraints acting on individual sleep.
In particular, we will perform a fine-grained description of sleep architecture and quality in the two studied populations. We will study how and why sleep naturally varies across individuals under normal vs. altered conditions (natural vs. captive populations) and how it changes when individuals face both parasite challenges (considering a large range of parasites) and experimental disruptions of their sleep. Additionally, we will study the physiological consequences of normal vs. altered and experimentally-disrupted sleep on cytokine production as well as on the production of stress hormones and cellular oxidative stress. Finally, sleep variation in normal vs. in altered conditions will be related to individual health and fitness thanks to long-term monitoring of the two populations.