When a hummingbird or a hawk moth sups on the sweet nectar of a wild tobacco plant, they're not just getting a tasty meal in exchange for their services in spreading the plant's pollen. Instead, a new study shows that the nectar
may be a complex chemical cocktail that simultaneously attracts and repels pollinators in order to optimize the amount of time they spend at each flower, and the attention they pay to flowers on different plants. "This paper shows just how sophisticated a plant can be in using chemistry to get what it wants," [The Scientist]
says lead researcher Ian Baldwin. The researchers had already analyzed the chemical composition of tobacco plants' nectar; they found that the compound benzyl acetone is the primary attractant, and that the plants "spike" their nectar with nicotine, presumably as a poisonous deterrent to insects. But in a clever experiment, the research team created genetically modified plants with different levels of these two chemicals.
In greenhouse and field experiments, the scientists were surprised to find that not only did nicotine deter nectar robbers and plant nibblers, but the right dose prevented pollinators from lingering too long at any one flower, increasing the number of flowers visited [Science News].
Tobacco plants can self-pollinate, researchers say, but the
plants, like other organisms, make an effort to “outcross” — mixing their genes with an unrelated mate — to get variation that could improve the odds that their young will survive [Science News].
By encouraging birds and insects to take small tastes of nectar from many different flowers, each tobacco plant increases its odds of creating beneficial genetic mixes. The study, published in the journal Science [subscription required], shows that the tobacco plants take a much more active role in boosting their reproductive chances than previously realized. Says Baldwin:
"The whole world of pollination biology was looking at it from the insect's perspective, rather than the plant's. Pollination is a complex activity, and every individual involved has its own agenda. The plant must play all sorts of sophisticated games in order to be pollinated but not have its nectar robbed" [Chemistry World].
Image: D. Kessler