Accumulation of phyllodulcin in sweet-leaf plants ofHydrangea serrata and its neutrality in the defence against a specialist leafmining herbivore |
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Authors: | Mami Ujihara Masateru Shinozaki and Makoto Kato |
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Institution: | (1) Biological Laboratory, Yoshida College, Kyoto University, Sakyo, 606-01 Kyoto, Japan;(2) Laboratory of Applied Botany, Faculty of Agriculture, Kyoto University, Sakyo, 606-01 Kyoto, Japan |
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Abstract: | Among wild plants ofHydrangea serrata (Hydrangeaceae) in Japan, there are sweet plants whose leave contain a kind of isocoumarin, phyllodulcin, which happens to
be 350 times as sweet as sucrose to the human tongue. In a primary beech forest in Ashu, Kyoto, the spatial distribution of
sweet plants and temporal and the spatial distribution of phyllodulcin within and among plants were investigated using a high
performance liquid chromatograph. The distribution of sweet plants was confined within a valley and was parapatric with non-sweet
plants. A plant's characteristic phyllodulcin accumulation did not change, even when transplanted into the different habitats.
The phyllodulcin content of the sweet plants varied greatly among plants, and the population mean peaked in July when the
plants flowered. Within a plant, phyllodulcin content was elevated by partial defoliation. We examined the possible effect
of phyllodulcin on herbivory by a specialist leafmining herbivore,Antispila hydrangifoliella (Lepidoptera: Heliozelidae). We transplanted sweet and nonsweet plants reciprocally between their original habitats, excluded
attacks by parasitoids, and compared performance of the leafminer. Leafminer colonization and larval survivorship on transplanted
andin situ plants was not significantly different between sites. The fact that accumulation of phyllodulcin did not augment a defensive
function, at least against herbivory by the leafminer, and the sporadic distribution of phyllodulcin-accumulating plants,
suggest that the genotypes synthesizing phyllodulcin emerged independently at separate localities by mutation, and that the
genotypes are almost adaptively neutral in defence against the specialist herbivore. |
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Keywords: | Hydrangea chemical defence leafminer Antispila phyllodulcin sweetener |
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