The Cape honeybee of South Africa seems at first like an ordinary bee. Like many bees, it lives in a colony where the only fertile individual is the queen, who returns from mating flights to lay eggs containing more workers, each pairing the genes of the queen and her mates. But in certain situations, in which the queen is absent or a worker happens upon another bee subspecies’ hive, a worker bee can rise up. Freed from the hormonal stranglehold that the queen usually maintains over the rest of the colony, she begins to lay eggs.
Each new bee is a perfect clone of herself. When they hatch, the rapidly reproducing clones can take wing and raven through the countryside in search of other subspecies’ hives, where they invade hapless victims’ nests, lay their own eggs, and act as parasites until the host colony collapses. But by then, other copies of the insubordinate worker have been born and flown over the horizon in search of new queens to dethrone.
In a bee, this is monstrously strange. Generally, colonies of bees and other social insects function like a single superorganism, with the many supporting the reproduction of the few. They are all so closely related that this amounts to helping themselves. When a Cape honeybee transforms from a placid social insect into a parasite, it’s doing something that appears outside the natural order. Ever since people discovered parasitic Cape honeybees inside collapsing colonies in South Africa, about a hundred years ago, beekeepers and biologists have considered: How does this happen? In a new paper out in Molecular Biology and Evolution, biologists provide the beginnings of an explanation, revealing that a single blip in the genetic code is the only difference between these bees and their peaceful siblings.
From a colony of wild Cape honeybees, the researchers sequenced the genomes of a number of individuals, half of whom were the parasites’ clones and half of whom were not. “We compared these two groups,” says Denise Aumer of the Martin-Luther-Universität Halle-Wittenberg, in Germany, a biologist and a lead author of the paper. “We found only a single locus in the whole genome where they differed significantly.” After decades of mystery, seeing this difference was striking, says Eckart Stolle, Aumer’s colleague and co–lead author: “It was super cool to find a strong signal like this, because you wouldn’t necessarily expect it.”
At that place, they found a one-letter difference between the bees’ genetic codes. Looking closer at the gene, the researchers determined that it codes for a little-studied protein lodged in the membrane of cells, which may be involved in trafficking substances in and out. They also discovered that for bees to switch into this parasitic mode, they must carry a certain version of a second gene. On its own, this gene is innocent of any wrongdoing, unless it winds up in a bee with the one-letter change. Other factors in the bee’s environment, like a weakening of the queen’s hormonal control or the changed bee’s arrival in a fresh host colony, must also align. But with these two genes, a bee is capable of the switch.
Intriguingly, the study explains an odd fact that beekeepers and scientists had independently noticed. It is not possible to breed a Cape honeybee with a closely related bee subspecies and wind up with parasitic offspring—they are always determinedly normal. The reason, it turns out, is quite simple. In Cape honeybees, that second, complementary gene originally comes from the father of the initial worker bee, while the one-letter difference comes originally from the queen, her mother. Thus, any Cape honeybee queen mated with a male from another subspecies will never yield children with both the pieces necessary for the transformation. And it’s probably not a bad thing—it means that no other bee species can pick up this exact behavior. But parasitic Cape honeybees are still a real pest in some parts of South Africa, with campaigns to eradicate them, Stolle notes.
Perhaps this ability, odd as it seems, has been beneficial for Cape honeybees in the evolutionary past. The researchers observed that the bees’ natural habitat is quite windy, and the ability of a worker to transform herself into a kind of queen might save colonies when their queens are blown off course and lost during mating flights. That single genetic change and the hormonal storm it must unleash might have meant the difference between total obliteration and bouncing back from a loss. Rather than a perversion, it might represent a kind of awe-inspiring, if slightly terrifying, flexibility in the face of disaster.
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