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The position of eyespots and thickened segments influence their protective value to caterpillars

Lookup NU author(s): Dr John Skelhorn, Giles Dorrington

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Abstract

It has long been believed that the paired circular markings ("eyespots") of Lepidoptera larvae, combined with their defensive postures (where the larvae swell their anterior body segments) protect them from potential predators. These traits could inhibit attacks by enhancing the similarity of the prey item to the predator's own natural enemies (notably snakes), but alternatively, they may simply exploit the predator's wariness of novel and/or conspicuous objects. To differentiate between these contrasting explanations, we evaluated the responses of naive chicks (Gallus gallus domesticus) to artificial caterpillar-like prey. In the first experiment, chicks were presented with model caterpillars either without eyespots or with eyespots positioned in 1 of 2 locations on their bodies: anteriorly or centrally. In the second experiment, chicks were presented with model caterpillars either lacking the thickening associated with the defensive posture, or with models in which a thickened section was placed centrally or anteriorly. In both cases, the chicks were significantly more wary of prey with anteriorly positioned defensive traits than either prey without these traits or prey with centrally positioned traits. Because prey with central eyespots and central thickening were equally novel and conspicuousness to those with these traits positioned in a more head-like anterior position, we infer that predator wariness was primarily influenced by the similarity of the prey to their potential natural enemies. These results support the idea that both caterpillar eyespots, and the defensive posture examined here, deter predators not simply because they are conspicuous, but because they enhance caterpillars' resemblance to potentially dangerous vertebrates.Predators are more wary of model caterpillars with eyespots and false heads placed anteriorly than those with these traits placed centrally. Many real caterpillars have anterior segments containing eyespots, which they inflate to create a "false head" when attacked. These traits could intimidate predators because they are conspicuous or because they make caterpillars resemble snakes. Our results support the latter explanation because the position of traits influenced models' resemblance to snakes but not their conspicuousness.


Publication metadata

Author(s): Skelhorn J, Dorrington G, Hossie TJ, Sherratt TN

Publication type: Article

Publication status: Published

Journal: Behavioral Ecology

Year: 2014

Volume: 25

Issue: 6

Pages: 1417-1422

Print publication date: 01/11/2014

Online publication date: 25/08/2014

Acceptance date: 18/07/2014

ISSN (print): 1045-2249

ISSN (electronic): 1465-7279

Publisher: Oxford University Press

URL: http://dx.doi.org/10.1093/beheco/aru154

DOI: 10.1093/beheco/aru154


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