U. ILLINOIS (US) — A new study of different types of bees—bumble bees, honey bees, stingless bees, and solitary bees—offers a first look at the genetic underpinnings of their different lifestyles.
Most people have trouble telling them apart, but these different bee species 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, says Gene Robinson, professor of entomology at University of Illinois 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,” Robinson says.
And there are other, so-called “primitively eusocial” insects, usually involving a single mother who starts a nest from scratch and then, once she has raised enough workers, “kicks back and becomes a queen.”
Sydney Cameron, professor of entomology and a collaborator on the study, dislikes the term “primitively eusocial” because it suggests that these bees are on their way to becoming more like stingless bees or honey bees.
Eusociality is not a progressive evolution from the “primitive” to the “advanced” stage, she says. “They’re not striving to become highly eusocial. They don’t say to themselves, ‘If only I could become a honey bee'”
“People talk about the evolution of eusociality,” Robinson says. “But we want to emphasize that these were independent evolutionary events. And we wanted to trace the independent stories of each.”
To accomplish this, the researchers sequenced active genes (those transcribed for translation into proteins) in nine species of bees representing every lifestyle from the solitary leaf-cutter bee, Megachile rotundata, to the highly eusocial dwarf honey bee, Apis florea.
Then co-author Matt Hudson, a professor of crop sciences, used the only available bee genome, that of the honey bee, Apis mellifera, as a guide to help assemble and identify the sequenced genes in the other species, and the team looked for patterns of genetic change that coincided with the evolution of the differing social systems.
“Are there genes that are unique to the primitively eusocial bees that aren’t found in the highly eusocial bees?” Cameron asks. “Or if you lump all the eusocial bees together, are there unique genes that unite those groups compared to the solitaries?”
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 report in a study published in the journal Proceedings of the National Academy of Sciences.
“What we find is that there are some genes that show signatures of selection across the different independent evolutions [of eusocial bees],” Robinson says. “They might be representatives of the ‘gotta have it’ genes if you’re going to evolve eusociality. But others are more lineage-specific.”
This study was made possible with a one-gigabyte sequencing grant from 454 Life Sciences (Roche Diagnostics Corporation) by way of the Roche 1GB contest. The National Science Foundation and the National Institutes of Health also supported the research.
The study team also included researchers from Cornell University and from the Program in Ecology, Evolution and Conservation Biology, and the Institute for Genomic Biology at the University of Illinois.
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