As Pollinators Decline, Plants Could Go It Alone

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The global decline in pollinators -- both wild and domesticated -- has scientists wondering if plants will adapt or die -- and the fate of a lot of our food hangs in the balance.

Some plant scientists now propose that many flowering plants could rapidly evolve strategies to avoid sinking with the pollinators, including self pollination and building tighter bonds with those pollinators that are still around.

"We consider two evolutionary scenarios that can occur in plant populations where cross-fertilization is made difficult" because of fewer pollinators, said researcher Pierre-Olivier Cheptou of UMR's Centre d'Ecologie Fonctionnelle et Evolutive in Montpeillier, France. Cheptou is a coauthor of a paper analyzing the two scenarios in the May 18 issue of the journal Trends In Plant Science.

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Some plants, just because of their evolutionary history, have within their genes what amounts to a tool box of potential quick changes that can make, Cheptou explained. One of them is to decrease the distance between the fertile male and female sexual organs of the flower -- making it possible to self-fertilize. This is a good way to avoid immediate extinction, but it has serious drawbacks, since it amounts to extreme inbreeding which can magnify lethal genetic problems.

But many plants are unable to self-fertilize even when pollinated by hand. For these plants a more likely adaptation is to improve its attractiveness to pollinators by, for instance, increasing the size of the flower petals, or some other change that brings them crowding in.

"My plants did a little of both," said plant researcher Sarah Bodbyl of Michigan State University's W. K. Kellogg Biological Station. She has conducted experiments with an Oregon monkey flower, Mimulus guttatus, to see if they would tend, after a few generations, towards self-pollination with fewer pollinators around -- which they did. They also, perhaps coincidentally, got slightly larger flowers.

In some cases wooing pollinators better could help the pollinators too, Cheptou pointed out. If, for instance, more pollinators are coming because they get more nectar from certain plants, that would be good for the pollinators. But if all they get is a flashier flower to look at, it's more difficult to see any advantage for pollinators, he said.

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And then, of course, there is a third evolutionary direction: extinction.

"If you lose your pollinator and can't adapt fast enough, you go extinct," said Bodbyl, adding that this is probably the most common scenario in the real world.

"For (some) plant populations adaptation to pollinator decline could not be possible at all because of the lack of genetic variance," agreed Cheptou. "We don't know what proportion of flowering plants could indeed adapt to the loss of pollinators." In other words, scientists are only beginning to understand how plants could adapt or die to the falling numbers of pollinators worldwide.