A beehive buzzes with thousands of genetically similar female honeybees. Some nurse their queen and her eggs while others fly out in search of pollen and nectar. For decades, scientists knew that bees took on new jobs as they aged, but a team of researchers recently discovered that chemical tags attached to the bees’ DNA play an important role in determining their career paths. The tags, which are frequently methyl groups, control gene expression, which in turn affects how an organism behaves. Both the chemical tags and the behavior they induce appear to be reversible, says Arizona State University biologist Gro Amdam. Foraging bees, for instance, could become nurses if the hive requires it. Humans also carry epigenetic tags that may affect their behavior. Scientists found methyl groups attached to a stress-hormone-receptor gene in child-abuse victims who committed suicide. If these chemical cues can be changed in bees, scientists may find new treatments for people with psychological trauma, mood disorders, and learning disabilities too.
To exploit the increase in available food, young bees that would normally become nurses immediately develop into foragers, a switch reflected by changes in their epigenetic tags.
An average hive has 10,000 to 50,000 workers. At any given time, foragers account for about 30 percent of the workforce, but that proportion can change depending on environmental factors.
When a queen gets old, she flees the hive with a swarm of mostly nurse bees, leaving the colony and its larvae to her successor. Some foragers and free-agent bees will then shift to nursing. In a lab experiment, after half of a hive’s population was taken away, only 10 percent of foragers became nurses. Scientists say that fragility may keep many foragers from making the switch. Foragers are programmed to be frail in order to protect the colony: Rather than bring infections or toxins back to the hive, they typically die out in the field.