Professor Co-Authors Article Featured In Science about Bee Eusociality

Honey Bee Colony. Submitted photo.

Honey Bee Colony. Submitted photo.

Several scientists including the Department’s own Dr. Spencer Johnston have published results in a recent edition of Science Magazine on how genetics can affect the eusociality of bees.

Led by Karen Kapheim, the team studied the genomes of ten bee species that had varied social complexity that represented multiple independent transitions in the evolution of social structures in the insects. Johnston said that the scientists wanted to answer the question on how genetics played a role in determining behavior in social insects, such as bees.

“Scientists have many questions they would like to ask of the genome sequence. Among these is, ‘How is behavior determined?’” he said.  “The honey bee, with its many complex behaviors seemed an obvious place to start in an effort to answer this question. The honey bee genome sequence is relatively small, complete and accurate. The genes have largely been identified and the information gained to date is readily available at a nationally known website for genetic data.”

Johnston said that comparative genetics seemed to be the way to address the behavior question. “The idea was, let’s sequence other bees with easily compared behaviors and see if we can find genome sequences that change in concert with the behavior,” he said.

The group compared 10 species of bees ranging from solitary species to higher, more complex social structures, such as those found in honey bees. Johnston said that he was engaged early in this process to measure the number of nucleotides in bees that seemed good candidates for this comparative study.

His findings had a profound influence on the direction of the study. He found that the small honey bee genome is the exception.

“Other bees can have up to 4 billion letters in their genomes. That meant a great deal more effort and that extra effort limited the number of species that could be compared,” he said “With that hurtle addressed, the sequences were generated for four bees with differing levels of social behavior, and comparable sequences from four other bees were added to the study as they became available.”

The comparison of the genome sequence and the level of social behavior provided answers that were fascinating. It isn’t the sequence itself that changes coincident with behavior.

The study found that the more social insects a human trait that to control the expression of genes by adding a simple CH3 (Methyl) group to one of the letters (usually a methyl group will be added to a C that is followed by a G). Johnston said that the more social the bee, the more genes that contain a methylated C and that the honey bee appeared to takes this methylation one step further than other organisms. “As honey bees age, they take on increasingly risky jobs. Only the oldest bees take the high risk jobs leaving the hive to forage and scout. Younger bees tend the queen and maintain the hive,” Johnston said. “What does that behavioral change have to do with these methylated Cs? Coincident with this change in behavior is a change in methylation. Older bees have less and less of their genes controlled (usually this also means a reduction in activity) by methylation of a CG couplet. Methylation appears to be a signature of social behavior.”

Johnston also said that he and the scientists also studied additional changes with sociality. They found out that the number of interacting genes (the gene network) grows increasingly complex as bees become more social. In the most extreme form (eusociality), where workers give up their own fertility to tend a sister (the queen) and her brood, he said that the level of networking is extensive.

“The increasing level of networking we observe as insects become more social raisesmany interesting questions. Does this same phenomenon occur in humans? Are altruists characterized by an increasingly complex gene network?” he said. How about other vertebrates? Is the complexity of the gene network one of the ways we differ from other primates? What about our favorite pet? Has domestication changed the level of networking? Some would even ask, do cats even have such a network?”

In the long run, Johnston said that the study of eusociality also is a study of humans and that further research needs to be done to learn more.

“We know a great deal about the sequence of letters in the human genome, but we have much more to learn. The sequence is inherited, but the changes we identified here are not in the sequence itself,” Johnston said. “The environment plays a role. Our future may depend upon knowledge of that role.”

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