A new study of bumble bees, honey bees, stingless bees and solitary bees has offered a first look at the genetic underpinnings of their differences in lifestyle.
Most people have trouble telling them apart, but these bees have home-lives that are as different from one another as a monarch’s palace is from a hippie commune or a hermit’s cabin in the woods. The study focuses on the evolution of “eusociality,” a system of collective living in which most members of a female-centric colony forego their reproductive rights and instead devote themselves to specialized tasks - such as hunting for food, defending the nest or caring for the young - that enhance the survival of the group. Eusociality is a rarity in the animal world, said Gene Robinson, a University of Illinois entomology professor and the director of the Institute for Genomic Biology, who led the study. Ants, termites, some bees and wasps, a few other arthropods and a couple of mole rat species are the only animals known to be eusocial.
Among bees, there are the “highly eusocial” honey bees and stingless bees, with a caste of sterile workers and a queen that functions primarily as a “giant, egg-laying machine,” said Robinson. And there are other, so-called “primitively eusocial” insects, usually involving a single mom who starts a nest from scratch and then, once she has raised enough workers, “kicks back and becomes a queen,” he said.
“People talk about the evolution of eusociality,” Robinson said. “But we want to emphasize that these were independent evolutionary events. And we wanted to trace the independent stories of each,” added Robinson.
The analysis did find significant differences in gene sequence between the eusocial and solitary bees. The researchers also saw patterns of genetic change unique to either the highly eusocial or primitively eusocial bees. The frequency and pattern of these changes in gene sequence suggest “signatures of accelerated evolution” specific to each type of eusociality, and to eusociality in general, the researchers reported.
“What we find is that there are some genes that show signatures of selection across the different independent evolutions (of eusocial bees),” said Robinson. “They might be representatives of the ‘gotta have it’ genes if you’re going to evolve eusociality. But others are more lineage-specific,” added Robinson.
The study is detailed in the Proceedings of the National Academy of Sciences.