Tropical plant picks and chooses who can pollinate it

Chuck Bednar for redOrbit.com – @BednarChuck

Not all plants just sit around waiting for pollinators to come to them – some can recognize when a high-quality pollinator is nearby and send signals designed to attract those creatures, according to research published this week in the Proceedings of the National Academy of Sciences.

In fact, in the study, Oregon State University ecologist Matthew Betts and his colleagues reveal that one exotic tropical plant known as the Heliconia tortuosa can recognize different types of hummingbirds by the way that they sip the flower’s nectar. In response, the red and yellow hued plant allows pollen to germinate, increasing the chances of successful seed formation.

I like big bills and I cannot lie

According to Science News, the researchers found that longer-billed hummingbirds are better at reaching in and guzzling nectar than shorter-billed ones, and the plant has adapted to only accept pollen from birds with bills that match the shape of its flowers. The authors claim that their study is the first to provide evidence that plants possess the ability to recognize pollinators.

Betts and his associates were actually studying H. tortuosa to find out if it was able to reproduce in regions where the rainforests of its native Costa Rica had become fragmented. However, when they tried to hand-pollinate the flowers, they discovered that the plant reproduced less than when it was simply left alone outside. So they set out to discover why this was happening.

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In an aviary at the Las Cruces Biological Station in Costa Rica, they exposed H. tortuosa to six different species of hummingbirds and one type of butterfly, and found that both the violet sabrewing and green hermit hummingbirds achieved an 80 percent success rate in fertilizing the plants. Both types of hummingbirds have long, curved bills that match the shape of the flowers, which apparently triggered the reproductive process in the plant.

By altering their hand pollinating techniques to mimic the two successful hummingbirds, Betts and his colleagues were able to achieve similar fertilization success rates. They also discovered one other shared characteristic among the two most effective types of pollinators: they traveled more widely across the landscape than the five other species, leading the researchers to believe that far-ranging species have more genetically-diverse pollen that benefits the plant.

“If the pollen’s from 20 meters away, the likelihood is it’s… from the plant’s own flowers or its brother or sister,” Betts told Science News. “But pollen from a long way away is unlikely to be related,” which would cut down on inbreeding and help keep the plants’ gene pool diverse. As a result, the H. tortuosa would have increased competitive fitness, the lead author noted.

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“The mechanism may have evolved to enable the plant to sort out pollinators that are likely to be carrying high-quality pollen from those carrying poor-quality pollen. It’s a big energy savings,” he added. “If you bother to make a seed and fruit every time you get pollen, that’s a lot of energy expenditure; you could be making a seed from your siblings’ genes. If you make a seed or fruit only from distant high-quality pollen, it could be an adaptive advantage.”

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