Parasite resistance and the adaptive significance of sleep

Abstract

Background: Sleep is a biological enigma. Despite occupying much of an animal's life, and having been scrutinized by numerous experimental studies, there is still no consensus on its function. Similarly, no hypothesis has yet explained why species have evolved such marked variation in their sleep requirements (from 3 to 20 hours a day in mammals). One intriguing but untested idea is that sleep has evolved by playing an important role in protecting animals from parasitic infection. This theory stems, in part, from clinical observations of intimate physiological links between sleep and the immune system. Here, we test this hypothesis by conducting comparative analyses of mammalian sleep, immune system parameters, and parasitism.

Brain–immune interactions and the neural basis of disease-avoidant ingestive behaviour

“…In addition, serum levels of ketone bodies, free fatty acids and glycerol rise from late afternoon until midnight by threefold to sevenfold [190], which represents another important fuel source for immune cells. It is noteworthy that infections lead to sickness behaviour, which increases sleep time and time in bed [12,55], thus also promoting allocation of energy-rich fuels to the activated immune system [191]. In this regard, it has been hypothesized that the circadian rhythms of the neuroendocrine and immune systems belong to an important programme necessary for provision of energy-rich fuels to daytime and night-time 'consumers' [10].…”

The ecological relevance of sleep: the trade-off between sleep, memory and energy conservation

“…In fact, the function of sleep has been a topic of much debate over the past 40þ years (Rechtschaffen 1998). Sleep may have some functions associated with energy conservation (Berger & Phillips 1995), immune function (Majde & Krueger 2005;Imeri & Opp 2009;Preston et al 2009), brain metabolism (Benington & Heller 1995), predation risk (Meddis 1975;Lima & Rattenborg 2007;Lesku et al 2008), neural maintenance (Kavanau 1996;Krueger & Obal 2003;Cirelli et al 2005;Tononi & Cirelli 2003 and/or memory consolidation (Stickgold & Walker 2005). Given the many possible benefits that sleep may provide, it would be short sighted to state that sleep has only one function.…”

“…Although we do not fully understand sleep, we know that it is a critically important behaviour (Cirelli & Tononi 2008;Mignot 2008). Even moderate sleep deprivation can have an adverse impact on immune function (Majde & Krueger 2005;Imeri & Opp 2009;Preston et al 2009), neurogenesis in the adult brain (GuzmanMarin et al 2005;Mueller et al 2008) and neural physiology (McDermott et al 2003). In some cases, extreme sleep deprivation can lead to death (Rechtschaffen & Bergmann 2002).…”

Global drivers of human pathogen richness and prevalence

“…They have also been identified as drivers of human behaviour (Fincher & Thornhill 2008a;Nettle 2009;Park & Schaller 2009;Preston et al 2009;Zhu 2009), the politics and political stability of countries (Thornhill et al 2009), human fertility (Guegan et al 2001), global economies (Thornhill et al 2009) and more generally the course and dynamics of human history (Denevan 1992;Morens et al 2004). Pathogen richness (the number of kinds), prevalence (number of cases) and their consequences vary dramatically among regions (figure 1a), as they have since humans first began to spread around the world (Wolfe et al 2007).…”