Parasitic bees reproduce without males

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An isolated population of honeybees, the cape bees, can reproduce without males.

Female worker bees in South Africa have found a way to procreate without males and ensure their offspring’s survival: by sneaking their eggs into other hives.

These bizarre abilities appear to be unique in the bee world, exhibited only by cape bees (Apis mellifera capensis), a subspecies of honeybee found in the far south of South Africa.

In most bee colonies, reproduction is sexual. It occurs between the queen bee and her devoted male workers while the female workers remain infertile.

In cape bee colonies, though, female workers use a unique form of cell division called thelytoky, which allows unfertilised eggs to produce female young. This process is found about 1,500 known animals, including some fish and reptiles.

Equally bizarre are the cape bee’s parasitic tendencies – when females reproduce on their own, they lay their eggs in foreign hives, allowing their young to feed off the resources of other colonies.

In these colonies, there is still a queen bee, and sexual reproduction still occurs. But if the queen bee is lost or killed, a new one can be produced by unfertilised eggs. The ability to reproduce asexually is then inherited by the next generation.

A team of researchers from Sweden and South Africa, led by Matthew Webster, a microbiologist at Uppsala University in Sweden, set about comparing the genomes of cape bees with those of related European and African species, hoping to identify the genes responsible for the development of these strange traits.

They surveyed the DNA of worker bees from two separate cape bee colonies. In both locations, worker bees produced almost exclusively female offspring.

According to the team’s findings, published in PLOS Genetics, the sets of DNA were remarkably similar across the bee species. However, they identified several genes that were starkly different when it came to cape bees.

These disparities, according to the researchers, may explain the development of asexual reproduction as well as the species’ parasitic behaviour – and the two traits may be linked.

The characteristics that allow for parasitism, for example, may also have been genetically selected for asexual reproduction.

Webster says the study helps scientists understand how genes control biological processes, such as cell division and behaviour.

“Understanding why populations sometimes reproduce asexually may help us to understand the evolutionary advantage of sex, which is a major conundrum for evolutionary biologists,” he says.

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