August 18, 2010
Sundews Just Want To Be Loved
Why do some insect-eating plants like sundews keep their flowers so far away from their traps? New research suggests that it isn't a clever trick to keep pollinators safe, it's about getting pollinated
Sex can be complicated at the best of times, but plants have an extra difficulty. If you're a plant who relies on insects to pollinate your flowers and reproduce, you will want your flowerstalks to be long. That way your flowers are on display to insects above the crowd. But if your stalk is too long, you'll stand out to herbivores, and you flower will end up as someone's lunch. It used to be thought that carnivorous plants like Sundews had the opposite problem. They reproduce better if they avoid eating insects that pollinate them, so a long stalk prevents an unfortunate meal. Simply looking at a plant, it's impossible to tell if the stalks evolved for sex or safety, but Bruce Anderson at the University of Stellenbosch has now found an answer to be published in the October issue of the Annals of Botany.
"But just because the stems didn't affect safety, it doesn't automatically follow that the other explanation, attracting pollinators, must be right by default. So I tested that too."
Flowers were cut from D. pauciflora and placed in test tubes. Some were set so the flowers were at normal height, while the other test tubes were buried so that the flower was barely above ground level. Anserson said: "Doing this meant there were few variables in the experiment. The flowers were identical. The only difference was their height. This way it's possible to simulate how well a Sundew that hadn't evolved a long stem could attract insects."
The results were emphatic. The taller flowers had ten times the number of visitors than the short flowers.
Anderson said: "There have been a few people who've suggested that the flower stalks are for attracting pollinators. However, the standard explanation in most textbooks is that the stems are to protect pollinators. It's a good story. It sounds like the kind of elegant solution that evolution comes up with. Now we have the hard data from these experiments and it shows that explanation is wrong. It's not about food, it's about sex. Sundews want to improve their chances of pollination and maximise their reproductive success."
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