Jan 22, 2018 | Updated: 09:54 AM EDT

Birds vs Bees: Flowers Evolved To Lure Specific Pollinators

Apr 22, 2017 09:20 PM EDT

It has always been believed that evolution of flowers has happened to lure pollinators. However, recent research hints that flowers visited by hummingbirds are not developing to attract birds, but confuse bumblebees. It makes bees seek out nectar in other flowers. This leaves the first set of plants to lure hummingbirds, which are more efficient as pollinators.

How do floral characteristics attract bumblebees? Robert Gegear, assistant professor of biology and biotechnology at Worcester Polytechnic Institute (WPI), studied bees flying among some paper representations of "hummingbird flowers" that were red with horizontal orientation as well as "bee flowers" that were lavender or blue and stood upright, according to ScienceDaily. Bee flowers tend to contain just small amounts of concentrated nectar. But the bird flowers contain more quantities of dilute nectar. It was found that hummingbird-pollinated flowers tend to evolve from bee-pollinated ancestors.

Often, flowering plants, as well as insect pollinators, are thought to be among the most significant examples of co-evolution on earth. Bees are thought to be one of the most important groups of flowering plant pollinators. There were 20,000 species depending only on resources from flowers, such as pollen and nectar, according to ScienceDirect.

Bird flowers are independent and make it tough for bees to access nectar or even see their red flowers. On the other hand, Gegear's paper shows that actually the traits "interact synergistically" so that bees can search in other places for nectar.

The team discovered that bees visited upright flowers, no matter what their color was. They also visited lavender flowers, without considering their orientation. However, when red flowers were shown to be in a horizontal orientation and lavender flowers were vertically oriented, like the natural flowers Mimulus cardinalis and Mimulus lewisii, the bumblebees did not visit them so often. Similarly, when the red color was combined with dilute nectar, the floral display and reward traits tend to interact in order to keep bees away.

Gegear says that bumblebees are generalists, maximize their reward intake and are not genetically programmed to visit only some special flowers. However, an ideal pollinator for the plant is a specialist, as it would make each plant get pollen only from its own species. By combining some floral characteristics, plants manipulate pollinators such that pollinating becomes less attractive to generalists.

The team's research showed that "the reason bee-to-bird evolutionary transitions are often accompanied by a floral shift to classic 'bird' trait complexes is because bees have a particularly difficult time combining red with other sensory traits, including nectar rewards," said Gegear. 

"It takes them longer to learn to seek out these combinations, and once they learn them, it takes them longer to recognize these flowers. Thus, bees avoid bird flowers in mixed floral environments because it makes economic sense for them to do so. When you put all this together, you find that 'bird flowers' are really 'anti-bee flowers' that function by exploiting specific sensory and cognitive limitations," he added.

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