Tonic immobility in cartilaginous fishes (Chondrichthyes): function, evolutionary history, and future directions
Gayford, Joel H., and Rummer, Jodie L. (2025) Tonic immobility in cartilaginous fishes (Chondrichthyes): function, evolutionary history, and future directions. Reviews in Fish Biology and Fisheries, 35. pp. 1301-1315.
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Abstract
Tonic immobility, a temporary cessation of voluntary movements, is a widespread phenomenon within the animal kingdom. While commonly regarded as an ‘anti-predator’ defence strategy, empirical evidence supporting this hypothesis is predominantly limited to terrestrial vertebrates. In Chondrichthyes (i.e., sharks, rays, and chimaeras), tonic immobility has also been proposed as an anti-predator mechanism, despite a dearth of evidence and fundamental physiological distinctions from terrestrial counterparts. Here, we present data regarding tonic immobility induced by dorsoventral inversion across 13 chondrichthyan species. We also perform a review of the existing literature to identify temporal, taxonomic, and methodological trends in TI research. Then, using phylogenetic comparative methods, we demonstrate that this trait is plesiomorphic to Chondrichthyes and has been independently lost multiple times throughout chondrichthyan phylogeny. Contrary to expectations, we find no significant correlation between the evolutionary transitions in tonic immobility and major ecological axes of variation in Chondrichthyes. Our findings challenge existing hypotheses and suggest that tonic immobility may lack adaptive significance in extant chondrichthyans, persisting through chondrichthyan phylogeny due to minimal net fitness costs. Additionally, we propose an association between the loss of tonic immobility and entanglement risk in shallow-water benthic ecosystems. Our results provide unprecedented insights into the evolutionary history of this enigmatic behaviour within Chondrichthyes and across the phylogeny of jawed vertebrates.
| Item ID: | 87581 |
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| Item Type: | Article (Research - C1) |
| ISSN: | 1573-5184 |
| Keywords: | Elasmobranchii, Evolution, Limp response, Plesiomorphy, Sharks, Thanatosis |
| Copyright Information: | © The Author(s) 2025. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. |
| Date Deposited: | 16 Jan 2026 03:23 |
| FoR Codes: | 31 BIOLOGICAL SCIENCES > 3103 Ecology > 310305 Marine and estuarine ecology (incl. marine ichthyology) @ 100% |
| SEO Codes: | 18 ENVIRONMENTAL MANAGEMENT > 1805 Marine systems and management > 180504 Marine biodiversity @ 100% |
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