Bees' Violet Preference Makes Sense

Bumblebees really, really like purple — and now we know why. New experiments with bumblebees that rove amongst the flowers near Würzburg, Germany, show that the inborn color preference gives the bees a good start in life.
The world’s a bit of a tough place for a naïve bee," said animal color perception researcher Adrian Dyer of La Trobe University in Australia. "They have to go out and find the goodies."

And any bee which innately prefers the color of flowers with the highest amounts of nectar will probably have a better chance of surviving its first few days in the world and then pass on that trait to its own offspring.

By comparing the colors of specific species of flowers and their nectar contents near Würzburg, and the color preferences shown by local newborn "naïve" Bombus terrestris bumblebees under laboratory conditions, researchers Nigel Raine and Lars Chittka of Queen Mary, University of London, found that there is a clear advantage to bees that start out life primed for purple.

"The purple flowers in that area near Würzburg are more rewarding," explained Raine.

By rewarding, he means they are unusually nectar-rich. Similar color preferences are found, but not previously explained, in several other bumblebee species from Asia, Europe and North America, Raine told Discovery News.

He and Chittka co-authored a paper on their study, which appears in the June 20 issue of the online journal PLoS ONE.

On the other hand, just because bumblebees come preloaded with a purple preference, doesn’t mean they are slaves to it, Raine pointed out.

"They’re very flexible in their foraging behavior," Raine said. "They can change their preference."

But unlike the purple preference, the advantages of flowers of other colors have to be learned by going out into the world and checking out what’s there.
Among the practical questions the new study may answer, observed Dyer, is a longstanding chicken-or-egg matter: Have flowers evolved and changed colors to attract the bees, or have bees evolved preferences that serve flowers?

The purple preference implies that some bees probably just had an individual, natural preference for purple flowers that turned out to be advantageous and inheritable. Because it served the bumblebees well, it led to more bees with the preference successfully reproducing until all bumblebees had the preference.

"It’s not the case that the bees had the preference first and the flowers followed," said Dyer.

This could have important implications for places like Australia, where bumblebees have not yet taken up residence, but could in the near future, he said. Tasmania saw its first bumblebees just 15 years ago, he noted.

The fact that flowers elsewhere seem to push bumblebees to evolve preferences could mean, for instance, that the flora of Australia might change the bumblebees more than vice versa.

Special Thanks to the Dicovery Channel