Global change processes such as urbanization are likely to affect sleep behavior, by altering abiotic (e.g., thermal and illumination) and biotic conditions (e.g., predation pressure) that influence sleep. However, little is known of how sleep behavior responds to urbanization and whether this response is flexible or conserved across populations. We quantified sleep site characteristics of the peninsular rock agama Psammophilus dorsalis in Bangalore city and surrounding rural areas. We find that P. dorsalis in urban areas display remarkable behavioral flexibility in response to the novel stressor of artificial light at night, being nine times more likely to use covered sleep sites that limit illumination, compared to lizards in rural areas. However, sleep sites in both populations were highly conserved in terms of substrate type (i.e., rocky with high surface rugosity) and their thermal properties. Our findings support behavioral amelioration of potentially adverse effects of night light in urban areas, even within the restricted availability of preferred substrates as sleep sites. Our study is one of the first to comprehensively compare sleep behavior in rural and urban areas and demonstrate substantial behavioral flexibility. The role of sleep behavior in the coping strategies of animals to urbanization needs further research attention.
Sleep is essential to animal life, yet it imposes certain costs such as making sleeping individuals vulnerable to predators. “Where” an animal sleeps (or its sleep site) is therefore important to ensure safety from predators but also to provide conducive environmental conditions. Cities can transform the availability of ideal sleep sites and can alter their thermal properties, in addition to being intensely illuminated by night light that hampers sleep. In this study, we compared sleep site characteristics of rural and urban populations of the peninsular rock agama Psammophilus dorsalis. We find that urban lizards sleep in sheltered sleep sites that shield them from night light but are highly dependent on rough, rocky substrates in both the city and rural areas. The remarkable flexibility in sleep behavior displayed by urban lizards is likely to help them cope in a city.
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The thermal image camera was acquired with a DST-FIST grant to the Center for Ecological Sciences. We would like to thank Adhith Swaminathan, Alissa Barnes, Anwesha Naskar, Avik Banerjee, Caleb Daniel, Chetan Rao, Dhanya Bharath, Gauri Gharpure, Pritha Dey, Shawn Dsouza, Subhasmita Patro, Tanmay Wagh, and Udita Bansal for help with fieldwork. We thank two anonymous reviewers for their valuable inputs to the manuscript.
This research was funded by the Indian Institute of Science’s Raman Post-doctoral Fellowship (to NPM), and the DBT-IISc partnership program.
Ethics approval for the study was granted by the Institutional Animal Ethics Committee, Indian Institute of Science (# CAF/Ethics/739/2020). All applicable international, national, and institutional guidelines for the use of animals were followed.
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The authors declare no competing interests.
Communicated by C. R Gabor.
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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
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Mohanty, N.P., Joshi, M. & Thaker, M. Urban lizards use sleep sites that mirror the structural, thermal, and light properties of natural sites. Behav Ecol Sociobiol 75, 166 (2021). https://doi.org/10.1007/s00265-021-03101-5
- Sleep ecology
- Artificial light at night
- Light pollution