Flowers Are Evolving To Have Less Sex

As the number of bees and other pollinators falls, field pansies are adapting by fertilizing their own seeds, a new study found. From a report: Every spring, trillions of flowers mate with the help of bees and other animals. They lure the pollinators to their flowers with flashy colors and nectar. As the animals travel from flower to flower, they take pollen with them, which can fertilize the seeds of other plants. A new study suggests that humans are quickly altering this annual rite of spring. As toxic pesticides and vanishing habitats have driven down the populations of bees and other pollinators, some flowers have evolved to fertilize their own seeds more often, rather than those of other plants.

Scientists said they were surprised by the speed of the changes, which occurred in just 20 generations. 'That's rapid evolution,' said Pierre-Olivier Cheptou, an evolutionary ecologist at the University of Montpellier in France who led the research. Dr. Cheptou was inspired to carry out the study when it became clear that bees and other pollinators were in a drastic decline. Would flowers that depend on pollinators for sex, he wondered, find another way to reproduce? The study focused on a weedy plant called the field pansy, whose white, yellow and purple flowers are common in fields and on roadsides across Europe. Field pansies typically use bumblebees to sexually reproduce. But they can also use their own pollen to fertilize their own seeds, a process called selfing.

Selfing is more convenient than sex, since a flower does not have to wait for a bee to drop by. But a selfing flower can use only its own genes to produce new seeds. Sexual reproduction allows flowers to mix their DNA, creating new combinations that may make them better prepared for diseases, droughts and other challenges that future generations may face. To track the evolution of field pansies in recent decades, Dr. Cheptou and his colleagues took advantage of a cache of seeds that France's National Botanical Conservatories collected in the 1990s and early 2000s. The researchers compared these old flowers with new ones from across the French countryside. After growing the new and old seeds side by side in the lab under identical conditions, they discovered that selfing had increased 27 percent since the 1990s.

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