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背景文章
The new study concerns the common milkweed plant (Asclepias syriaca) and the aphids and ants that call it home. All three species depend on each other: the aphids drink the plant's sap and defecate a sweet syrup called honeydew, which ants eat. In return, the ants kick predators off the plant, protecting both the milkweed and the aphids in the process.Any biologist looking at milkweeds as a whole would see this mutualism play out, but community ecologists Kailen Mooney of the University of California, Irvine, and Anurag Agrawal of Cornell University wondered if the relationship held on a plant-by-plant basis. To find out, the researchers planted 320 milkweeds in an old field full of ant nests, picking 10 plants each from 32 genetically distinct families of full siblings. The team returned throughout the summer to census the insects that colonized the plants.
Plant genetics made a huge difference in insect dynamics. For 20 of the 32 plant families, ants helped the aphids as expected by increasing the aphid population more than 150% over that on ant-free plants in the same family. But for the remaining 12 plant families, the ants actually decreased the aphid populations by more than half. This averages out to ants boosting aphid populations overall but reveals a previously unimagined role for milkweeds in changing the relationship between the two insects, Mooney and Agrawal report in this month's issue of The American Naturalist.
The researchers suggest that the milkweed has an interest in manipulating the ant-aphid relationship: Plants that use their aphids to attract more ants win protection against herbivores食草动物 such as caterpillars, the team showed in another experiment. But that protection comes at a price--water and sugar the plants lose to the sap-sucking aphids, for example. For some genotypes, it apparently makes sense to have fewer aphids. |
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发表于 2012-7-25 22:59:27
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