Details

Autor(en) / Beteiligte

• Hossie, Thomas John
• Skelhorn, John
• Breinholt, Jesse W.
• Kawahara, Akito Y.
• Sherratt, Thomas N.

Titel

Body size affects the evolution of eyespots in caterpillars

Ist Teil von

• Proceedings of the National Academy of Sciences - PNAS, 2015-05, Vol.112 (21), p.6664-6669

Ort / Verlag

United States: National Academy of Sciences

Erscheinungsjahr

2015

Link zum Volltext

Quelle

MEDLINE

Beschreibungen/Notizen

• 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 × 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 naïve domestic chicks in a laboratory setting following a 2 × 3 design (small or large size × 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). Significance Eyespots are a widespread form of antipredator defense that have long captured the imagination of evolutionary biologists, geneticists, psychologists, and artists. These markings are particularly common within Lepidoptera, and eyespots on caterpillars have been shown to deter avian predators; however, why eyespots have evolved in particular caterpillar species, and why they are not even more widespread, remain unclear. Here we answer this question using a powerful three-pronged approach. Our phylogenetically controlled analysis of hawkmoths demonstrates that eyespots are typically restricted to large caterpillars, and our field and laboratory experiments provide an explanation for this. Eyespots are costly to small caterpillars because they enhance detectability without providing a protective advantage, but they are beneficial to large caterpillars because they deter predators.