Marginal Eyespots on Butterfly Wings Deflect Bird Attacks Under Low Light Intensities with UV Wavelengths

Marginal Eyespots on Butterfly Wings Deflect Bird Attacks Under Low Light Intensities with UV Wavelengths.

Martin Olofsson, Adrian Vallin, Sven Jakobsson, Christer Wiklund

PLoS ONE 5(5): e10798. doi:10.1371/journal.pone.0010798

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Depuis une discussion qui commence à être vieillotte avec Jean Staune au sujet de Kallima inachis où Jean vois une chiée d’empreintes du doigt de Dieux, je me suis toujours demandé à quoi ressemblent les ailes de cette bestiole sous éclairage UV. Dès que je trouve un moyen de me connecter à PLoS (dont le système de connexion et de trackbaks pue, je poserai la question aux auteurs. Ils ont l’équipement UV, peut-être ils ont aussi quelques Kallima…

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a. Distribution of blue tit attacks under high light intensity in the presence of UV wavelengths (High, UV+, n = 13). b. Distribution of blue tit attacks under low light intensity in the presence of UV wavelengths (Low, UV+, n = 14). c. Distribution of blue tit attacks under low light intensity in the absence of UV wavelengths (Low, UV-, n = 13).

Background: Predators preferentially attack vital body parts to avoid prey escape. Consequently, prey adaptations that make predators attack less crucial body parts are expected to evolve. Marginal eyespots on butterfly wings have long been thought to have this deflective, but hitherto undemonstrated function.
Methodology/Principal Findings: Here we report that a butterfly, Lopinga achine, with broad-spectrum reflective white scales in its marginal eyespot pupils deceives a generalist avian predator, the blue tit, to attack the marginal eyespots, but only under particular conditions—in our experiments, low light intensities with a prominent UV component. Under high light intensity conditions with a similar UV component, and at low light intensities without UV, blue tits directed attacks towards the butterfly head.
Conclusions/Significance: In nature, birds typically forage intensively at early dawn, when the light environment shifts to shorter wavelengths, and the contrast between the eyespot pupils and the background increases. Among butterflies, deflecting attacks is likely to be particularly important at dawn when low ambient temperatures make escape by flight impossible, and when insectivorous birds typically initiate another day’s search for food. Our finding that the deflective function of eyespots is highly dependent on the ambient light environment helps explain why previous attempts have provided little support for the deflective role of marginal eyespots, and we hypothesize that the mechanism that we have discovered in our experiments in a laboratory setting may function also in nature when birds forage on resting butterflies under low light intensities.