The ecology of sleep in non-avian reptiles Nitya P. Mohanty 1 * , Carla Wagener 2 , Anthony Herrel 3 and Maria Thaker 1 1 Centre for Ecological Sciences, Indian Institute of Science, Bangalore, 560 012, India 2 Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Stellenbosch, Western Cape, 7600, South Africa 3 Département Adaptations du Vivant, MECADEV UMR7179 CNRS/MNHN, Paris, France ABSTRACT Sleep is ubiquitous in the animal kingdom and yet displays considerable variation in its extent and form in the wild. Eco- logical 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 con- text of sleep in non-avian reptiles remains understudied and without systematic direction. In this review, we examine mul- tiple 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 phys- iology (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. Key words: sleep ecology, sleep ecophysiology, roost, retreat, refuge, inactivity, anti-predator, thermoregulation, evolu- tion, Squamata CONTENTS I. Introduction ......................................................................... 2 II. Methods ............................................................................ 4 III. Summary of sleep literature ............................................................. 4 IV. Sleep traits ........................................................................... 5 (1) Habitat selection ................................................................. 5 (a) Sleep sites .................................................................... 5 (b) Spatio-temporal distribution of sleep sites ........................................... 8 (2) Behaviour, morphology, and physiology ............................................... 8 (a) Sleep posture and position ....................................................... 8 (b) Colour patterns while sleeping .................................................... 9 (c) Sleep architecture ............................................................ 10 (3) Inter-individual interactions ........................................................ 11 (a) Aggregations ................................................................ 11 (b) Ontogenetic and sex differences .................................................. 11 V. Evolutionary consequences ............................................................. 11 VI. Applied sleep ecology in an altered world .................................................. 12 VII. Prospectus .......................................................................... 12 VIII. Conclusions ......................................................................... 13 IX. Acknowledgements and author contributions ............................................... 14 * Address for correspondence (Tel: +91 6366796410; E-mail: nitya.mohanty@gmail.com) Biological Reviews (2021) 000–000 © 2021 Cambridge Philosophical Society. Biol. Rev. (2021), pp. 000–000. 1 doi: 10.1111/brv.12808