Orchids' Lips Evolved to Lure Pollinators

Orchids, like humans, use their lips to attract and entice others, and now new research finds that intense competition underlies their formation and constant changes.

Two competing groups of proteins are engaged in an evolutionary war that helps to explain why orchids are so beguiling and come in many different shapes and sizes, according to a new study published in the latest issue of the journal Nature Plants.

Co-author Chang-Hsien Yang and his colleagues found that the protein complex "L" (for lip) and the protein complex "SP" (for standard petals) of orchids compete to promote the different shapes. If the proteins for lip formation win out, then the orchid will develop a big, prominent lip. If the competing complex wins, then flowers will develop where all of the petals look about the same. A mixture of the two creates a less obvious lip and countless variations.

An orchid lip is important because "it acts as a landing pad or serves as a platform for potential pollinators, such as insects, moths and butterflies," Yang, a professor in the Graduate Institute of Biotechnology at the National Chung Hsing University, told Discovery News.

"The lip also acts as the main pollinator attractant by employing visual, fragrance and tactile cues," Yang added. "All of these are important for giving orchids a great evolutionary advantage by promoting reproduction."

It's not hard to figure out that this bee orchid hopes to attract bees and other pollinators. When seen from above, it looks like a bee-shaped puppet.

The "come hither" look of orchids, such as this member of the genus Phalaenopsis, ties with their sexy appearance.

Barbara Gravendeel, who co-authored a Nature Plants "News & Views" piece about the latest orchid research, told Discovery News that while bees are very intelligent insects, they really do think that they are mating with another bee when they land on many orchids.

The mistake is understandable, considering that many orchids smell, feel and look like bee bodies.

The new research adds to the growing body of evidence that plants can be clever and develop effective, flexible survival strategies, even though they do not possess a brain. Here, an orchid from the Serapia genus is being pollinated by a bee, which believes he is having sex with another bee.

Gravendeel who is chair of the Biodiversity Department at the University of Applied Sciences, Leiden, explained that many orchids always flower at the beginning of the bee mating season, bursting open a week before female bees emerge above ground.

"Only un-experienced male bees that emerge a bit earlier than the females are fooled into mating with orchid flowers that look, smell and feel like female bees," she said.

In many cases, the orchid provides only a good time with no food reward, but by the time the bee figures this out, the orchid already received what it wants and needs: pollination.

"The male bees only need to be tricked twice: once for removing pollen from one orchid flower, and then once more for depositing this pollen on the stigma of another plant, ensuring pollination and subsequent fertilization and reproduction of the orchid," Gravendeel explained.

She added, "Once the real female bees appear above ground, the male bees quickly learn the difference and do not mate with orchid flowers anymore. These orchids have been pollinated by then, though, so there is no need to fool any more bees."

A moth orchid such as this is colorful enough to human eyes, with its beautiful hints of purple and yellow, but when seen from a pollinator's perspective, the flower is even more attractive. Honeybees, for example, cannot see the color red, but they can see a color that we cannot. It's known as "bee's purple," which is a mixture of yellow and ultraviolet.

Orchids dazzled renowned British naturalist Charles Darwin too. He predicted that many orchids co-evolved with pollinators, such that their shapes should match the bodies of these other beneficial organisms. The new research provides evidence for Darwin's prediction, Yang said, with the competition between the two protein complexes being part of the co-evolution process.

Read more at Discovery News