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Bees Can Switch Roles Epigenetically


-- Monty Python, "Eric the Half-Bee" Song

For the first time, scientists have witnessed a behavioral change via epigenetic markers, with no change to the genes themselves.

Honeybees start out their lives as nurses, spending their time in the hive taking care of the queen's eggs. After two or three weeks, they take to the fields outside in a new role as foragers. Scientists have wondered how an insect with the same genetic makeup makes the transition to a completely different behavior. It's two bees in one! The solution of the enigma appears to be in the epigenetic code.

Science Daily reported this discovery by Johns Hopkins University ("How Bees Decide What to Be: Reversible 'Epigenetic' Marks Linked to Behavior Patterns"). The discovery hints at a sea change in how biologists will view genetics from now on: "what is believed to be the first evidence that complex, reversible behavioral patterns in bees -- and presumably other animals -- are linked to reversible chemical tags on genes." (Emphasis added.)

Using a new search tool, the researchers mapped the methyl tags -- a variety of epigenetic marker -- on the genes of nurse bees and forager bees. Though the genes were the same, 155 methyl tags had changed between them. The scientists believe these tags reside on regulatory genes known to affect the status of other genes. The tags regulate gene expression traffic: "Gene sequences without these tags are like roads without stoplights -- gridlock," remarked Andy Feinberg, director of the Center for Epigenetics at JHU.

Next, the team cleansed the hive of nurses and allowed returning foragers to adapt to the nursing shortage. The bees that reverted to the nursing role were mapped again. Remarkably, they found that more than half of the methyl tags reverted to their earlier nursing state. Of the reverted tags, 57 were on genes likely involved in the behavior of the different roles. Team member Gro Amdam commented,

"It's like one of those pictures that portray two different images depending on your angle of view," she says. "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."
New Scientist used a computer metaphor, likening the change to a "reboot of brain genes" back to the nursing role. "Worker honeybees shuttling between foraging and nursing tasks have been found to switch huge groups of genes on and off in their brains for each job."

What this implies (for humans as well as bees) is that behavioral changes might have reversible epigenetic settings. "It's the first evidence, to our knowledge, of an epigenetic change linked to reversible behavior in any organism," Feinberg said. "It opens doors to new ways of thinking about human problems like addiction, and about learning and memory."

Psychiatric disorders like addiction, schizophrenia and bipolar disorder, as well as aging and other chronic conditions like obesity are known to have an epigenetic component. So a better understanding of how epigenetics and behavior interact could lead to new treatments.
Fascinating. Yet there is this that is left unexplained: what master control knows how and when to switch these particular 155 methyl tags on and off? It can't be random. Imagine a chimpanzee at a switchboard flipping switches without a plan, each switch causing cascading effects on downstream systems. Chaos would result.

Honeybee roles involve hierarchies of control. Nurse bees with one predefined role, involving particular behaviors and skills, have to make a radical switch to another predefined role (forager) with very different tasks and skills. What reprograms the right tags at the right time? Some master control, like fingers on a keyboard, signals them to "Stop nursing and go forth into the fields; bring back nectar and dance for your mates."

It appears certain that evolutionary theory, with its dependence on genetic point mutations or other unplanned accidental changes, is hopelessly inadequate to explain this finding. If a single-base mutation on a gene is already unlikely to produce a benefit, how much more would a random change be utterly unable to correctly order all the switches that must work simultaneously to produce a complex behavior, like foraging?

When you think of it, foraging includes numerous skills: navigation, remote sensing, targeting, memory, and communication, to name a few. Another article on Science Daily recently showed that bumblebees, with their tiny brains, solve the "traveling salesman problem," a difficult algorithm in computational complexity theory.

Two new levels of complexity above the already-complex genes have come into view here: an epigenetic switchboard, as described by the ENCODE project, and a master controller yet to be elucidated. This appears to be a promising area of research for a theory equipped with the epistemic resources to handle complex systems of this magnitude: intelligent design.

Image credit: lamoix/Flickr.