SCIENCE

The Evolution of the Orchid and the Orchid Bee

Which came first—the plant or its pollinator?

September 23, 2011

Most orchid bees, like this Euglossa paisa, have metallic coloration. S. Ramirez, 2005

When scientists delve into studies of the co-evolution of plants and their pollinators, they have something of a chicken/egg problem—which evolved first, the plant or its pollinator? Orchids and orchid bees are a classic example of this relationship. The flowers depend on the bees to pollinate them so they can reproduce and, in return, the bees get fragrance compounds they use during courtship displays (rather like cologne to attract the lady bees). And researchers had thought that they co-evolved, each species changing a bit, back and forth, over time.

But a new study in Science has found that the relationship isn’t as equal as had been thought. The biologists reconstructed the complex evolutionary history of the plants and their pollinators, figuring out which bees pollinated which orchid species and analyzing the compounds collected by the bees. It seems that the orchids need the bees more than the bees need the flowers—the compounds produced by the orchids are only about 10 percent of the compounds collected by the bees. The bees collect far more of their “cologne” from other sources, such as tree resin, fungi and leaves.

And it was the bees that evolved first, the researchers found, at least 12 million years before the orchids. “The bees evolved much earlier and independently, which the orchids appear to have been catching up,” says the study’s lead author, Santiago Ramirez, a post-doc at the University of California at Berkeley. And as the bees evolve new preferences for these chemical compounds, the orchids follow, evolving new compounds to lure back their bee pollinators.

But this study is more than just an interesting look into the evolution of two groups of organisms. The researchers note that in the context of the current decline of bee populations worldwide, their research has disturbing implications for what that decline might mean for plants. “Many of these orchids don’t produce any other type of reward, such as nectar, that would attract other species of bee pollinators,” Ramirez notes. “If you lose one species of bee, you could lose three to four species of orchids.”

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