Leaf Colour as a Signal of Chemical Defence to Insect Herbivores in Wild Cabbage
(Brassica oleracea)
#MMPMID26353086
Green JP
; Foster R
; Wilkins L
; Osorio D
; Hartley SE
PLoS One
2015[]; 10
(9
): e0136884
PMID26353086
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Leaf colour has been proposed to signal levels of host defence to insect
herbivores, but we lack data on herbivory, leaf colour and levels of defence for
wild host populations necessary to test this hypothesis. Such a test requires
measurements of leaf spectra as they would be sensed by herbivore visual systems,
as well as simultaneous measurements of chemical defences and herbivore responses
to leaf colour in natural host-herbivore populations. In a large-scale field
survey of wild cabbage (Brassica oleracea) populations, we show that variation in
leaf colour and brightness, measured according to herbivore spectral
sensitivities, predicts both levels of chemical defences (glucosinolates) and
abundance of specialist lepidopteran (Pieris rapae) and hemipteran (Brevicoryne
brassicae) herbivores. In subsequent experiments, P. rapae larvae achieved faster
growth and greater pupal mass when feeding on plants with bluer leaves, which
contained lower levels of aliphatic glucosinolates. Glucosinolate-mediated
effects on larval performance may thus contribute to the association between P.
rapae herbivory and leaf colour observed in the field. However, preference tests
found no evidence that adult butterflies selected host plants based on leaf
coloration. In the field, B. brassicae abundance varied with leaf brightness but
greenhouse experiments were unable to identify any effects of brightness on aphid
preference or performance. Our findings suggest that although leaf colour
reflects both levels of host defences and herbivore abundance in the field, the
ability of herbivores to respond to colour signals may be limited, even in
species where performance is correlated with leaf colour.
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