The ecology of sleep in non‐avian reptiles

Abstract

Sleep is ubiquitous in the animal kingdom and yet displays considerable variation in its extent and form in the wild. Ecological factors, such as predation, competition, and microclimate, therefore are likely to play a strong role in shaping characteristics of sleep. Despite the potential for ecological factors to influence various aspects of sleep, the ecological context of sleep in non‐avian reptiles remains understudied and without systematic direction. In this review, we examine multiple aspects of reptilian sleep, including (i) habitat selection (sleep sites and their spatio‐temporal distribution), (ii) individual‐level traits, such as behaviour (sleep postures), morphology (limb morphometrics and body colour), and physiology (sleep architecture), as well as (iii) inter‐individual interactions (intra‐ and inter‐specific). Throughout, we discuss the evidence of predation, competition, and thermoregulation in influencing sleep traits and the possible evolutionary consequences of these sleep traits for reptile sociality, morphological specialisation, and habitat partitioning. We also review the ways in which sleep ecology interacts with urbanisation, biological invasions, and climate change. Overall, we not only provide a systematic evaluation of the conceptual and taxonomic biases in the existing literature on reptilian sleep, but also use this opportunity to organise the various ecological hypotheses for sleep characteristics. By highlighting the gaps and providing a prospectus of research directions, our review sets the stage for understanding sleep ecology in the natural world.

Urban lizards use sleep sites that mirror the structural, thermal, and light properties of natural sites

“…Additionally, we document several natural history information pertaining to the sleep behavior of P. dorsalis that were previously unrecorded. When using vegetation at night, P. dorsalis was found on thin unstable perches, which has been hypothesized to aid in early detection of approaching predators via tactile cues (Anderson 1998); similar use of thin perches is seen in several reptile taxa (reviewed in Mohanty et al 2021). The suggested role of visual cues in aiding predator detection at night (Clark and Gillingham 1990;Mohanty et al 2016), however, is not fully supported in the case of P. dorsalis, as sleeping lizards were positioned in all possible head directions as opposed to a predominantly "inward" direction that would enable visual detection of a predator approach.…”

“…The predominant use of walls as sleep sites also explains the lower likelihood of horizontal and angular sleep perch orientations in urban areas (though the 95% confidence interval spans zero). Perch orientation could have implications for sleep quality, but this relationship remains to be examined in reptiles (Mohanty et al 2021). Furthermore, as compared to diurnal perch height (mean ± SE for urban = 4.38 ± 0.21 m; rural = 5.91 ± 0.57 m; , nocturnal perches of P. dorsalis are considerably lower (urban = 0.99 ± 0.04 m; rural = 1.21 ± 0.06 m).…”

“…Therefore, ecological processes are likely to shape sleep behavior and its associated traits, to minimize the costs of sleep (Anderson 1984;Lima et al 2005). For example, characteristics of sleep sites in the wild are often This article is a contribution to the Topical Collection Using behavioral ecology to explore adaptive responses to anthropogenic change -Guest Editors: Jan Lindström,Constantino Macias Garcia, Caitlin Gabor specialized with respect to their structure and microclimate to provide suitable thermo-hydric conditions and safety from predators (Anderson 1998;Mohanty et al 2021). Apart from sleep sites, a suite of sleep traits pertaining to physiology (e.g., sleep duration), morphology (e.g., color during sleep), and behavior (e.g., sleep posture), as well as inter-individual interactions (e.g., conspecific aggregations), constitute the sleep ecology of a species (Mohanty et al 2021).…”

“…Our understanding of how sleep behavior is affected by urbanization has several knowledge gaps. Firstly, response of sleep to factors associated with urbanization has been limitedly studied in wild populations and rarely in reptiles (Mohanty et al 2021). This assumes further importance as sleep in reptiles is perhaps more sensitive to ALAN than in birds and mammals, due to the presence of a light-sensitive pineal eye in this group of vertebrates (Mohanty et al 2021).…”

“…Firstly, response of sleep to factors associated with urbanization has been limitedly studied in wild populations and rarely in reptiles (Mohanty et al 2021). This assumes further importance as sleep in reptiles is perhaps more sensitive to ALAN than in birds and mammals, due to the presence of a light-sensitive pineal eye in this group of vertebrates (Mohanty et al 2021). Secondly, there is a lack of comprehensive, systematic studies on urban sleep sites, especially with respect to their structural, thermal, and light conditions.…”