A Phylogenetic Analysis of Sleep Architecture in Mammals: The Integration of Anatomy, Physiology, and Ecology

Abstract

Among mammalian species, the time spent in the two main "architectural" states of sleep--slow-wave sleep (SWS) and rapid-eye-movement (REM) sleep--varies greatly. Previous comparative studies of sleep architecture found that larger mammals, those with bigger brains, and those with higher absolute basal metabolic rates (BMR) tended to engage in less SWS and REM sleep. Species experiencing a greater risk of predation also exhibited less SWS and REM sleep. In all cases, however, these studies lacked a formal phylogenetic and theoretical framework and used mainly correlational analyses. Using independent contrasts and an updated data set, we extended existing approaches with path analysis to examine the integrated influence of anatomy, physiology, and ecology on sleep architecture. Path model structure was determined by nonmutually exclusive hypotheses for the function of sleep. We found that species with higher relative BMRs engage in less SWS, whereas species with larger relative brain masses engage in more REM sleep. REM sleep was the only sleep variable strongly influenced by predation risk; mammals sleeping in riskier environments engage in less REM sleep. Overall, we found support for some hypotheses for the function of sleep, such as facilitating memory consolidation or learning, but not others, such as energy conservation.

The Phylogeny of Sleep Database: A New Resource for Sleep Scientists

“…Based on these considerations, the use of sleep quotas has long been a standard measure used in comparative tests, (Elgar AB 1988) [11] (Elgar AB 1990) [12] (Lesku AN 2006) [13] (Zepelin ES 1989) [14] and is the basis for construction of our database on sleep quotas.…”

Predation and the phasing of sleep: an evolutionary individual-based model

“…For example, Capellini et al (2008a) found that sleep durations are shortened when animals have high metabolic rates for their body size, consistent with foraging constraints that limit the time available for sleep. Capellini et al (2008a) also found that when animals are more exposed to predation at sleep sites, their sleep durations decline (see also 3 Allison & Cicchetti 1976;Lesku et al 2006). In another study, these authors used phylogenetic methods to investigate the factors that influence the phasing of sleep (Capellini et al 2008b; see also Tobler 1989;Ball 1992).…”

“…One recent comparative study, for example, found that the number of white blood cells covaries positively with sleep durations across species ), while other studies found that sleep characteristics covary with aspects of brain size (Lesku et al 2006;Capellini et al 2009). Many recent phylogenetic comparative studies have focused on sleep duration, including the duration of rapid eye movement (REM) and non-rapid eye movement (NREM) sleep (e.g., Lesku et al 2006;Capellini et al 2008a). Other fundamental questions concern the phasing of sleep throughout the 24-hour cycle (Tobler 1989;Ball 1992).…”

“…A variety of benefits have been proposed for sleep, including benefits related to memory consolidation, energy conservation and immune function (Meddis 1983;Zepelin et al 1989;Berger & Phillips 1995;Stickgold 2005;Lesku et al 2006;Capellini et al 2009;Preston et al 2009). One recent comparative study, for example, found that the number of white blood cells covaries positively with sleep durations across species ), while other studies found that sleep characteristics covary with aspects of brain size (Lesku et al 2006;Capellini et al 2009). Many recent phylogenetic comparative studies have focused on sleep duration, including the duration of rapid eye movement (REM) and non-rapid eye movement (NREM) sleep (e.g., Lesku et al 2006;Capellini et al 2008a).…”

“…Lima et al 2005). Based on comparative studies in mammals, it appears that predation influences sleep patterns, at least in terms of sleep durations (Allison and Cicchetti 1976;Berger & Phillips 1995;Lesku et al 2006;Capellini et al 2008a). Evidence also exists for changes in prey sleep patterns when individuals are exposed to predators (e.g., Lesku et al 2008).…”