Today, with seemingly all the English-speaking world abuzz over the wedding of Prince William and Kate Middleton, let us turn to royal couplings I actually care about—as should you. After all, the future of the British monarchy may rest with Will and Kate but the future of much of the world’s food supply depends on these others: the honeybee queens and the lucky, lucky drones that they take as their kings (for a few seconds of airborne lovin’). The bees can’t rival the royals in the sheer spectacle of their nuptials, but we humans could still learn a few things from them about organization and breeding.
Traditionally, royal European families such as the Hapsburgs arranged marriages with one another to consolidate their political alliances. Good statecraft made for bad genetic hygiene, however, as the level of inbreeding gradually increased, leading to high rates of hemophilia, physical deformities and other problems. In the 18th century, Charles II, the last of Spain’s Hapsburg kings, suffered from so many abnormalities—not to mention a highly protrusive “Hapsburg lip”—that he was nicknamed “the Hexed.”
Honeybees might at first seem predisposed to a similar inbreeding problem. Three days after emerging from the cell where she was nurtured, a young virgin queen bee flies out of her hive in search of mates; during mid-air couplings, she may collect sperm from a dozen of them, which she will portion out to fertilize eggs for the rest of her life. (The drones die immediately after mating with her because their penises are torn out of their bodies in the process.) But of course, the first males the queen might encounter could easily be her own sibling drones, who have also gone a-courting. Such matings do sometimes happen, but they seem to yield unusually few offspring.
Moreover, genetic diversity directly contributes to the health of a hive. In a 2006 study appearing in the Proceedings of the Royal Society of London B, Thomas D. Seeley of Cornell University and David R. Tarpy of North Carolina State University demonstrated that honeybee colonies spawned from a single male were more vulnerable to disease than were those from 10 matings. How can the queen find so many different mates, however, without flying immense distances?
The honeybees’ solution was to invent their own version of the college mixer. Males from many colonies gather within flying spaces called drone congregation areas (DCAs), typically 10 to 40 meters above the ground and upward of 30 meters across. Queens then make their way to the DCAs and inject themselves into this cloud of randy drones to mate on the wing with a number of them. The no-longer-virgin queen then returns to the hive for a lifetime of babymaking, the lucky but eviscerated drones fall from the skies, and the unsuccessful drones either try again at another DCA or go home to sulk.
A curious and somewhat mysterious fact about the DCAs is that they always form at the same locations, year after year—even though none of the drones visiting them survive across the seasons. Drones commonly go to DCAs between two and three kilometers from their hives, though they have been known to go at least two or three times that far. When drones leave their colonies, they don’t fan out across the landscape randomly. Rather, they seem to favor certain flyways, or paths, adjacent to lines of trees or other geographic features. (Drones and queens won’t fly over water, it seems.) These flyways branch periodically, often where those landscape guides shift direction, too. The DCAs form directly above these branch points but at a much higher elevation. In the early 1990s, Gerald M. Loper of the U.S. Department of Agriculture and his colleagues used radar to map the movements of drones within 10 square kilometers of a commercial apiary: they measured 18 kilometers of flyways and at least 26 DCAs.
The formation of DCAs obviously improves a queen’s shot at finding as many different fathers for her future brood—but it wouldn’t be foolproof. If drones lived up to their reputation (among us humans, anyway) as lazy, they could simply hang out in the DCAs closest to their home colonies, or in ones closest to other colonies, thereby sparing themselves excess travel. But they don’t.
In 1998, as described in the Proceedings of the Royal Society B, Emmanuelle Baudry of the CNRS and her colleagues examined the genetic diversity among 142 drones taken from a DCA in Germany. They found that the relatedness among the drones very nearly followed a Poisson distribution. To quote from the abstract (emphasis added):
Therefore, colonies were apparently equally represented in the drone congregation, and calculations showed that the congregation comprised males that originated from about 240 different colonies. This figure is surprisingly high. Considering the density of colonies around the congregation area and the average flight range of males, it suggests that most colonies within the recruitment perimeter delegated drones to the congregation with an equal probability, resulting in an almost perfect panmixis. Consequently, the relatedness between a queen and her mates, and hence the inbreeding coefficient of the progeny, should be minimized. The relatedness among the drones mated to the same queen is also very low, maximizing the genetic diversity among the different patrilines of a colony.
Somehow, then, the drones from any one colony equally distribute themselves around all the DCAs in their vicinity—a feat of self-organization that strikes me as impressive, given that the drones have no obvious way of determining how many brothers they have and how many DCAs are around, and that the DCAs form even in the absence of queens (so the drones can’t follow trails of pheromones).
Also, I would be curious to read an informed analysis of how well or poorly this strategy works for the drones with respect to passing along their own genes. Granted, by participating in this arrangement, the drones help to ensure plenty of healthy outbreeding for all the colonies in the vicinity, which has to be good for the drones’ legacy. But it also means they hugely dilute their chances of passing on their genes (directly, and indirectly through their brothers) by competing with drones from every colony in the area, rather than, say, strategically ganging up in the DCAs near some other hive.
At least that how it seems to me. I’d welcome any corrections or thoughts that you readers might have to offer.
—Ahh, royal marriages. They always come down to power and politics, don’t they?
Update, 11:15 a.m.: For more on inbreeding among the European royals, see Luke Jostins’ post at Genomes Unzipped on “Inbreeding, Genetic Disease and the Royal Wedding.” But also see David Dobbs’ story for National Geographic on “The Risks and Rewards of Royal Incest.”
Baudry, E., M. Solignac, L. Garnery, M. Gries, J.M. Cornuet and N. Koeniger 1998. Relatedness among honeybees (Apis mellifera) of a drone congregation. Proc. R. Soc. Lond. B. 265: 2009-2014. doi: 10.1098/rspb.1998.0533
Loper, G.M., W.W. Wolf and O.R. Taylor, Jr. 1992. Honey bee drone flyways and congregation areas – radar observations. J. Kan. Entomol. 65: 223-230 (www.jstor.org/stable/25085360).
Seeley, T.D. and Tarpy, D.R. Queen promiscuity lowers disease within honeybee colonies. Proc. R. Soc. B 7 January 2007 274 (1606): 67-72. doi:10.1098/rspb.2006.3702
Underhill, Richard. “The Queen Bee Makes a Mating Flight,” The Peace Bee Farmer (peacebeefarm.blogspot.com/2009/05/queen-bee-makes-mating-flight.html).
Collison, Clarence. “A Closer Look—Drone Congregation Areas,” Bee Culture, Sept. 1, 2008 (www.beeculture.com/storycms/index.cfm?cat=Story&recordID=603).