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Body size affects the evolution of eyespots in caterpillars

Lookup NU author(s): Dr John Skelhorn


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Many caterpillars have conspicuous eye-like markings, called eyespots. Despite recent work demonstrating the efficacy of eyespots in deterring predator attack, a fundamental question remains: Given their protective benefits, why have eyespots not evolved in more caterpillars? Using a phylogenetically controlled analysis of hawkmoth caterpillars, we show that eyespots are associated with large body size. This relationship could arise because (i) large prey are innately conspicuous; (ii) large prey are more profitable, and thus face stronger selection to evolve such defenses; and/or (iii) eyespots are more effective on large-bodied prey. To evaluate these hypotheses, we exposed small and large caterpillar models with and without eyespots in a 2 x 2 factorial design to avian predators in the field. Overall, eyespots increased prey mortality, but the effect was particularly marked in small prey, and eyespots decreased mortality of large prey in some microhabitats. We then exposed artificial prey to naive domestic chicks in a laboratory setting following a 2 x 3 design (small or large size x no, small, or large eyespots). Predators attacked small prey with eyespots more quickly, but were more wary of large caterpillars with large eyespots than those without eyespots or with small eyespots. Taken together, these data suggest that eyespots are effective deterrents only when both prey and eyespots are large, and that innate aversion toward eyespots is conditional. We conclude that the distribution of eyespots in nature likely results from selection against eyespots in small caterpillars and selection for eyespots in large caterpillars (at least in some microhabitats).

Publication metadata

Author(s): Hossie TJ, Skelhorn J, Breinholt JW, Kawahara AY, Sherratt TN

Publication type: Article

Publication status: Published

Journal: Proceedings of the National Academy of Sciences of the United States of America

Year: 2015

Volume: 112

Issue: 21

Pages: 6664-6669

Online publication date: 26/05/2015

Acceptance date: 14/04/2015

ISSN (print): 0027-8424

Publisher: National Academy of Sciences


DOI: 10.1073/pnas.1415121112


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Funder referenceFunder name
Natural Sciences and Engineering Research Council of Canada
Newcastle University
IOS 1121739National Science Foundation