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Evidence for Sleep in Sharks and Rays: Behavioural, Physiological, and Evolutionary Considerations
Michael L Kelly1,2,3, Shaun P Collin2,3,4, Jan M Hemmi1,2
1School of Biological Sciences, The University of Western Australia, Perth, Washington, Australia.
Brain, Behavior and Evolution
|November 28, 2019
Summary
Research on cartilaginous fish sleep is limited. Evidence suggests some sharks and rays may sleep, but continuously swimming species show no signs of sleep, requiring further study.
Area of Science:
- Comparative physiology
- Neuroscience
- Evolutionary biology
Background:
- Sleep is a fundamental biological process observed across diverse animal taxa.
- Significant gaps exist in our understanding of sleep patterns in aquatic vertebrates, particularly cartilaginous fishes.
- Sharks and rays, as early vertebrate lineages, offer unique insights into sleep evolution.
Purpose of the Study:
- To comprehensively review existing literature on sleep and activity patterns in cartilaginous fishes (sharks and rays).
- To identify current evidence for sleep states in these species and highlight knowledge gaps.
- To propose future research directions for understanding sleep in sharks and rays.
Main Methods:
- Exhaustive literature search of over 80 laboratory and field studies.
- Analysis of activity patterns, observed sleep behaviors, and electrophysiological data.
- Comparative review of sleep evidence in cartilaginous versus bony fishes.
Main Results:
- Preliminary evidence for sleep exists in sharks and rays that do not require continuous swimming for respiration.
- Currently, there is no evidence for sleep in continuously swimming fish species.
- The evolutionary history of sleep may be illuminated by studying these basal vertebrates.
Conclusions:
- Sleep in cartilaginous fishes is not well-documented, with preliminary findings for some species.
- Continuously swimming sharks and rays present a unique challenge for understanding sleep.
- Further research is crucial to determine how, when, and why sharks and rays sleep, and its evolutionary implications.
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