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Summary: Evidence from the domestication of apple for the
maintenance of autumn colours by coevolution
Marco Archetti*
Department of Zoology, University of Oxford, South Parks Road, OX1 3PS Oxford, UK
The adaptive value of autumn colours is still a puzzle for evolutionary biology. It has been suggested that
autumn colours are a warning signal to insects that use the trees as a host. I show that aphids (Dysaphis
plantaginea) avoid apple trees (Malus pumila) with red leaves in autumn and that their fitness in spring is
lower on these trees, which suggests that red leaves are an honest signal of the quality of the tree as a host.
Autumn colours are common in wild populations but not among cultivated apple varieties, which are no
longer under natural selection against insects. I show that autumn colours remain only in the varieties that
are very susceptible to the effects of a common insect-borne disease, fire blight, and therefore are more in
need of avoiding insects. Moreover, varieties with red leaves have smaller fruits, which shows that they have
been under less effective artificial selection. This suggests a possible trade off between fruit size, leaf colour
and resistance to parasites. These results are consistent with the hypothesis that autumn colours are a
warning signal to insects, but not with other hypotheses.
Keywords: autumn colours; apple; aphid; photoprotection; coevolution; domestication
1. INTRODUCTION
(a) Autumn colours
Many trees and shrubs of the temperate regions change
their leaf colour in autumn. The biochemistry and the
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