Proceedings of the Royal Society B: Biological Sciences
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Autumn leaves seen through herbivore eyes

Thomas F Döring

Thomas F Döring

Department of Life Sciences, Imperial College LondonSilwood Park Campus, Ascot, Berkshire SL5 7PY, UK

School of Biological and Chemical Sciences, Queen Mary, University LondonLondon E1 4NS, UK

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,
Marco Archetti

Marco Archetti

Department of Zoology, University of OxfordSouth Parks Road, Oxford OX1 3PS, UK

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and
Jim Hardie

Jim Hardie

Department of Life Sciences, Imperial College LondonSilwood Park Campus, Ascot, Berkshire SL5 7PY, UK

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Published:https://doi.org/10.1098/rspb.2008.0858

    Why leaves of some trees turn red in autumn has puzzled biologists for decades, as just before leaf fall the pigments causing red coloration are newly synthesized. One idea to explain this apparently untimely investment is that red colour signals the tree's quality to herbivorous insects, particularly aphids. However, it is unclear whether red leaves are indeed less attractive to aphids than green leaves. Because aphids lack a red photoreceptor, it was conjectured that red leaves could even be indiscernable from green ones for these insects. Here we show, however, that the colour of autumnal tree leaves that appear red to humans are on average much less attractive to aphids than green leaves, whereas yellow leaves are much more attractive. We conclude that, while active avoidance of red leaves by aphids is unlikely, red coloration in autumn could still be a signal of the tree's quality, or alternatively serve to mask the over-attractive yellow that is unveiled when the green chlorophyll is recovered from senescing leaves. Our study shows that in sensory ecology, receiver physiology alone is not sufficient to reveal the whole picture. Instead, the combined analysis of behaviour and a large set of natural stimuli unexpectedly shows that animals lacking a red photoreceptor may be able to differentiate between red and green leaves.

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