A Whiff of Bee Evolution

There is a whole network out there that goes undetected by our eyes, ears, or even our wireless devices. Bees, specifically orchid bees, utilize complex olfactory signals in their quest for mates. Even more impressively, they are the only currently confirmed animals that use mating pheromones entirely derived from their environment. Similar to how Darwin's finches evolved varied beaks according to niches, each species of these bees has its own blend of pheromones.

Even within species, everything from the number of components in the fragrance to the quantity of this fragrance differs, but the largest differences are between different species. This may seem obvious, but it shows how vital these collected scents are to orchid bees — this is how female bees keep from mating with the wrong species.

The strong relationship between these bees and their orchids makes them ideal for evolutionary studies. Santiago Ramírez from Harvard University partnered with Professor Yvonne Zimmerman and Thomas Eltz from the Sensory Ecology Group at the University of Düsseldorf to look at orchid bees for lessons on evolution. These researchers improvised male orchid bee lures from scented, nylon-wrapped Wiffle balls, which dangled from the trees of a jungle-island in the middle of the Panama Canal, capturing different species depending on how each ball was scented. The resulting study was published in Ecology last year.

"One can attract males by using synthetic compounds that are chemically identical to those produced by the flowers," explained Ramírez, who dutifully hung the Wiffle balls through rain and mosquitoes. Such efforts paid off. The researchers compared the genetic distance between the various orchid bee species and the chemical divergence in their pheromones. They found that the fragrance composition is one of the first things to diverge during speciation, indicating that smell in these bees has a profound influence on their biological identity.

Why go through all the trouble to figure out how these bees evolved in the first place?

"If you see a strong correlation between two traits, and you take phylogeny into account, you are making sure that such correlation is real and not simply an artifact of common descent," said Ramírez.

Because of their efforts to map these bees on an evolutionary tree and link their fragrance differences with these relationships, the researchers now think that some of the orchids on the islands adapted to accommodate the bees' search for scents. It's a case of evolutionary history revealing itself through data on interspecies adaptation.

Using this information, these scientists have also been able to contribute to knowledge about the bees' foraging behavior and even spatial memory. The stories of bees' pasts and their role in shaping the evolution of other organisms, along with their own, are now being pieced together through the way this invisible communication diversified.

Be sure to check out Sophie Robinson's post about the worldwide decreasing numbers of bees here on Student Voices.

Image Credit: http://wikimedia.org (Marten Sepp)

References:

1. Zimmermann, Y., Ramírez, S. R., & Eltz, T. Chemical niche differentiation among sympatric orchid bees. Ecology 90, 2994–3008 (2009).