Datura & moth mutualism
Why do the plants continue to cooperate with such a costly partner, and indeed to attract and reward it above all other possible pollinators?
Most plant require animal pollinators in order to reproduce. Pollinators move pollen between flowers as they seek out nectar, sugar-rich liquid they require to fuel their busy lives. Nectar is not cheap for plants to produce, but generally the pollination benefits that nectar-feeders confer is worth the investment. Oddly, though, sometimes pollinators inflict direct damage on their food plants. Such is the case in the relationship between the jimsonweed (Datura wrightii) and the hawkmoth Manduca sexta. These large moths are outstanding pollinators, and visit the massive, white, night-blooming, nectar-rich jimsonweed flowers with great regularity. In fact, the moths feed from almost no other flowers, and the plants have almost no other pollinators. This certainly looks like a win-win situation. But Manduca exacts a heavy toll for its services. After a nectar meal, female moths commonly lay eggs on the leaves. The caterpillars grow into the huge hornworms you may encounter destroying your tomato plants. Just as they do on tomatoes, the hornworms consume many or even all of jimsonweed’s leaves. Why do the plants continue to cooperate with such a costly partner, and indeed to attract and reward it above all other possible pollinators? These are questions that my students and I are actively investigating.
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