Oolon Colluphid
27 Apr 2009, 11:10 AM
... is to scare off parasitic insects.
'Research Highlights' from Nature 458, 949 (23 April 2009)
Evolution: Bitter apple
In spring, aphid larvae emerge from eggs laid on host plants and head for the leaves to feed. But, for at least one aphid species (Dysaphis plantaginea), those whose parents laid eggs on apple tree (Malus pumila) hosts with red leaves in the autumn do less well than those laid on trees with yellow or green leaves. Marco Archetti of the University of Oxford, UK, says that this supports the theory that red leaves serve as an 'honest' signal to insects warning against such factors as robust chemical defences.
Domesticated apple trees were selected for nice fruit, not insect resistance, and as such should not advertise defences they have not retained. Accordingly, Archetti finds that domesticated apples rarely have red leaves in autumn. There might even be a direct trade-off; red-leaved trees make smaller, less palatable apples.
Royal Society Proceedings B
Published online before print April 15, 2009, doi: 10.1098/rspb.2009.0355
Evidence from the domestication of apple for the maintenance of autumn colours by coevolution
Marco Archetti
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.
'Research Highlights' from Nature 458, 949 (23 April 2009)
Evolution: Bitter apple
In spring, aphid larvae emerge from eggs laid on host plants and head for the leaves to feed. But, for at least one aphid species (Dysaphis plantaginea), those whose parents laid eggs on apple tree (Malus pumila) hosts with red leaves in the autumn do less well than those laid on trees with yellow or green leaves. Marco Archetti of the University of Oxford, UK, says that this supports the theory that red leaves serve as an 'honest' signal to insects warning against such factors as robust chemical defences.
Domesticated apple trees were selected for nice fruit, not insect resistance, and as such should not advertise defences they have not retained. Accordingly, Archetti finds that domesticated apples rarely have red leaves in autumn. There might even be a direct trade-off; red-leaved trees make smaller, less palatable apples.
Royal Society Proceedings B
Published online before print April 15, 2009, doi: 10.1098/rspb.2009.0355
Evidence from the domestication of apple for the maintenance of autumn colours by coevolution
Marco Archetti
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.