The secret behind virgin birth in South African bees

Researchers from The University of Sydney have identified the single gene that determines how South Africa’s Cape honey bees reproduce without ever having sex.

Writing in the journal Current Biology, the scientists revealed that the gene GB45239, on chromosome 11, is responsible for the virgin births. Reversions to asexual reproduction are rare in nature, so this may be the first time that the genetic basis of such a phenomenon has been discovered.

“It is extremely exciting,” said Professor Benjamin Oldroyd, a behavioural geneticist at The University of Sydney. “Scientists have been looking for this gene for the last 30 years. Now that we know it’s on chromosome 11, we have solved a mystery.”

In the Cape honey bee (Apis mellifera capensis), GB45239 has allowed worker bees to lay eggs that only produce females instead of the normal males that other honey bees do. “Males are mostly useless,” Prof Oldroyd said, “but Cape workers can become genetically reincarnated as a female queen and that prospect changes everything.”

But this also causes problems: “Instead of being a cooperative society, Cape honey bee colonies are riven with conflict because any worker can be genetically reincarnated as the next queen. When a colony loses its queen, the workers fight and compete to be the mother of the next queen.”

The ability to produce daughters asexually, known as “thelytokous parthenogenesis”, is restricted to this single honey bee subspecies. Several other traits distinguish the Cape honey bee from other subspecies; in particular, the ovaries of worker bees are larger and more readily activated and they are able to produce queen pheromones, allowing them to assert reproductive dominance in a colony.

These traits also lead to a propensity for social parasitism — a behaviour where Cape bee workers invade foreign colonies, reproduce and persuade the host colony workers to feed their larvae. Every year in South Africa, 10,000 colonies of commercial beehives die because of the social parasite behaviour in Cape honey bees.

The existence of Cape bees with these characters has been known for over a hundred years, but it is only recently, using modern genomic tools, that we have been able to understand the actual gene that gives rise to virgin birth. According to Prof Oldroyd, “Further study of Cape bees could give us insight into two major evolutionary transitions: the origin of sex and the origin of animal societies.”

Perhaps the most exciting prospect arising from this study is the possibility to understand how the gene actually works functionally, with Prof Oldroyd saying, “If we could control a switch that allows animals to reproduce asexually, that would have important applications in agriculture, biotechnology and many other fields. For instance, many pest ant species like fire ants are thelytokous, though unfortunately it seems to be a different gene to the one found in capensis.”

Image caption: Cape honey bee workers laying parasitic eggs on a queen cell. Image credit: Benjamin Oldroyd.

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