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Born to be selfish: Capensis workers are Queen wannabees



7 July 2010

Image caption: Worker of the Cape honey bee subspecies, who are able to give birth to female offspring, pictured next to a queen cell in which worker-laid eggs are clearly visible (inside the white circle). Photo courtesy of Ben Oldroyd.
Image caption: Worker of the Cape honey bee subspecies, who are able to give birth to female offspring, pictured next to a queen cell in which worker-laid eggs are clearly visible (inside the white circle). Photo courtesy of Ben Oldroyd.

Some individuals are just born selfish, and research by Michael Holmes has shown that in Cape honey bees, Apis mellifera capensis, some workers are genetically predisposed to committing the ultimate act of selfishness - tricking other workers into raising their clonal daughter as the new queen.

Published in the journal Molecular Ecology in June 2010 and highlighted in the 19 June issue of New Scientist, the study reveals the extraordinary fact that Cape honey bee workers with particular genotypes can activate their ovaries and start producing potential queens much earlier than other workers - thereby increasing their chances of reincarnating themselves the colony's queen.

The study by Michael Holmes, conducted as part of his Honours research under the supervision of Associate Professor Madeleine Beekman and Professor Ben Oldroyd in the School of Biological Sciences, involved the fascinating Cape honeybee from South Africa, which has a completely unique mode of reproduction.

"Bees are social insects with reproductive division of labour, which means the queen reproduces for the colony and the female workers are sterile in her presence. But normal worker bees are capable of producing male offspring," says Michael who is now a PhD student in the School of Biological Sciences working on reproductive conflicts in honey bees.

"But amazingly, Cape honey bee workers give birth to female offspring who are clones of themselves. And if your genetically-identical daughter becomes the queen, then in genetical terms, you become the queen."

The unusual reproduction of Cape honey bees led Beekman and Oldroyd to hypothesise that workers would try to produce queens whenever the colony goes through its normal reproductive cycle. As expected they found that in colonies preparing to produce new queens, workers activated their ovaries and laid eggs in queen cells, some of which were successfully reared as queens by fellow workers.

"The aim of my project was to find out how soon after queen-loss did workers start to produce new queens. And we were also curious to see if workers, when given a choice, would prefer to rear queen brood that was laid by workers, or the queen herself," explains Michael.

Michael removed queens out of eight Cape honey bee colonies and found that workers immediately laid eggs in queen cells. He also showed that workers have no preference for rearing queen-laid eggs that were introduced days after workers began to lay, suggesting that certain sneaky workers had completely fooled their own sisters into raising their daughters as queens - a behaviour termed reproductive parasitism.

Not only did the authors find eggs of the colony's own workers in the queen cells, they also found that unrelated Cape honey bees were infiltrating the colony and laying eggs in queen cells.

"Combined, our results provide compelling evidence that certain genotypes of the Cape honey bee are specialised to live a life of reproductive selfishness - quite the opposite of the traditional view of a harmonious beehive full of dutiful worker daughters," says Michael.


Contact: Carla Avolio

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