“When there are too few nurses, the foragers can step in and take their places, reverting to their former practices,” said Amdam. The researchers used this strategy to see whether foraging bees would maintain their foraging genetic tags when forced to start acting like nurses again. So they removed all of the nurses from their hives and waited several weeks for the hive to restore balance.

That done, the team again looked for differences in DNA methylation patterns, this time between foragers that remained foragers and those that became nurses. One hundred and seven DNA regions showed different tags between the foragers and the reverted nurses, suggesting that the epigenetic marks were not permanent but reversible and connected to the bees’ behavior and the facts of life in the hive.

Dramatically, Feinberg noted, more than half of those regions had already been identified among the 155 regions that change when nurses mature into foragers. These 57 regions are likely at the heart of the different behaviors exhibited by nurses and foragers, explained Amdam.

“It’s like one of those pictures that portray two different images depending on your angle of view,” said Amdam. “The bee genome contains images of both nurses and foragers. The tags on the DNA give the brain its coordinates so that it knows what kind of behavior to project.”

The researchers say they hope their results begin to shed light on complex behavioral issues in humans, such as learning, memory, stress response and mood disorders, which all involve interactions between genetic and epigenetic components similar to those in the study. A person’s underlying genetic sequence is acted upon by epigenetic tags, which may be affected by external cues to change in ways that create stable – but reversible – behavioral patterns.

Authors of the paper include Gro Amdam and Florian Wolschin, ASU School of Life Sciences in the College of Liberal Arts and Sciences, and the Norwegian University of Life Sciences, Brian Herb, Kasper Hansen, Martin Aryee, Ben Langmead, Rafael Irizarry and Andrew Feinberg from The Johns Hopkins University. This work was funded through the NIH Director's Pioneer Award through the National Institute of Environmental Health Sciences (# DP1OD008324), the Research Council of Norway and the Pew Charitable Trust.