The eye, students of evolution learn, is so useful an adaptation that it has emerged numerous times in the history of life. The ancestors of bats and birds, too, evolved the capacity for flight independently.

But limbs and organs aren’t the only features to emerge though convergent evolution. A eusocial lifestyle, where worker castes toil for the good of the community and often a queen, has evolved at least 11 times among insects.

Now, a genomic study of different bee species suggests that even when insects evolve eusociality independently, they often use the same genes and molecular pathways.

“There seem to be some genes that are common in the evolution of eusociality. You can call it a toolkit,” says Gene Robinson, an entomologist at the University of Illinois in Urbana, who led the new study, published this week in Proceedings of the National Academy of Sciences.

The study came together after Robinson’s lab won a contest with a prize of one billion letters of DNA sequencing from the life-sciences company Roche.

They sequenced genes expressed in the brains and abdomens of nine bee species, representing three separate origins of eusociality. Robinson’s team chose the brain because of its likely role in social behaviour, and the abdomen because genes expressed in reproductive organs might reveal differences between hyper-fertile queens and sterile workers. The honeybee, Apis mellifera, provided a complete genome sequence with which to compare the other species’ DNA.

The billion base pairs yielded sequences of more than three thousand genes present in all nine species. Next, Robinson’s team scoured these sequences for signs of rapid evolutionary change – a sign of natural selection at work – in the eusocial bees. This identified 212 genes, including some involved in sugar metabolism and gland development, potentially part of the eusocial ‘toolkit’.

Sugar metabolism, the team speculates, could be important because eusocial bees tend to eat more highly processed carbohydrates than solitary species. Gland development also makes sense because social insects rely more heavily on chemical communication than their solitary relatives.

Robinson’s team also compared highly eusocial bees with large colonies and a rigid caste system, such as honey bees, with less eusocial species, where colonies are smaller and castes are more fluid. Here, 173 genes appeared to be evolving only in highly eusocial bees, while another 218 were under selection in the primitively eusocial insects.

Many of the genes under selection in the primitively eusocial bees were related to brain function, including a gene involved in learning and memory called dunce. Robinson’s team speculates that the fluid social structures of these bee species require more cognitive resources than life in a eusocial insect society where relations and roles are set.

The researchers also found genes and pathways under selection in sole species of eusocial bee. “The take home message of this paper is the mosaic story,” Robinson says. “There do seem to be genes that are specific to individual lineages involved in the evolution of eusociality,” he says.

Much more work will be needed to figure out how the genes Robinson’s team identified could explain the evolution of euosciality, or whether they are involved at all. Some of the genes could be evolving as a consequence of a eusocial lifestyle, rather than being its cause. The next step will be to determine if the genes identified make proteins that differ from those made by solitary bees, Robinson says.

However, Gro Amdam, a biologist at Arizona State University in Tempe, says that the evolution of eusociality may not have depended on changes in the shape and function of proteins. Subtler genetic tweaks, influencing where and when genes are active, will also prove important.

Robinson’s study would miss most of these changes, because they tend to occur in regions of the genome that don’t encode proteins. But “it’s very cool that they do find a signature also in coding genes,” Amdam adds. “I don’t think there’s any mutually exclusive idea for how you achieve a eusocial lifestyle.”

Image of a honey bee queen via Wikimedia Commons