The effects of body size, activity, and phylogeny on primate sleeping ecology

Objectives Sleeping ecology plays a key integrative role in the primates' lives. Selecting an adequate sleeping site is therefore critical, but both extrinsic (e.g., predation, thermoregulation) and intrinsic factors (e.g., body size, circadian activity) need to be considered simultaneously. There is, however, a notable lack of comprehensive comparative analyses of sleeping ecology within primates. We explored the links among body size, circadian activity, and sleeping site choice in phylogenetically controlled comparative analyses across all major primate lineages. Materials and Methods We compiled published information on body size, circadian activity, and sleeping site choice of extant primates. We performed ancestral state reconstructions for the different sleeping sites and used comparative phylogenetic analyses to quantify associations between sleeping site preference, body size and circadian pattern. Results Comparative analyses across 390 species revealed that primate sleeping site usage was best predicted by circadian activity patterns. Nocturnal species were more likely to use tree holes and nests, whereas diurnal primates were more likely to sleep on trees. Ancestral reconstructions indicated a relative ambiguity among states for several nodes, especially within strepsirrhines, whereas "on trees" was the most likely sleeping site type within haplorrhines. Discussion The main intrinsic predictor of sleeping site choice in primates has links to two extrinsic factors: predation risk and thermoregulation. Thermoregulatory and anti-predator benefits accrue for nocturnal species that rest in nests or tree holes. Body size only poses a constraint for shelter use in larger species. Comparative studies of resting ecology are integral for reconstructing primate evolution and for revealing complex adaptations in arboreal mammals.