Honeybees in a hive have different fixed roles, or castes, even though their DNA sequence is often identical. What then decides these differing roles and are there any epigenetic changes that parallel these differences? On page 1371, Herb and colleagues provide some answers to these questions.

It is already known that a deciding factor for the role assigned to a honeybee is its care early in life: female larvae that are fed more royal jelly (a protein-rich secretion from glands in worker bees' heads) grow into queen bees, whereas larvae destined to be worker bees only get limited amounts of this secretion. Queen bees are in charge of laying eggs, whereas worker bees take on differing roles at different ages, ranging from cleaning cells to carrying water.

Such differences in phenotype on the basis of early-life care are suggestive of an epigenetic influence. Accordingly, the authors used whole-genome bisulfite sequencing and high-throughput methylation analysis to look at differences in DNA methylation between sister bees.

Herb and colleagues found no DNA methylation differences between newly emerging worker and queen bees, but did uncover differences between two worker subcastes: nurse bees, which feed other bees, and foragers, which travel outside of the hive to collect food. Although the queen bee's behavior is fixed, and it cannot switch to being a worker, the roles of these worker subcastes are not fixed, and nurse bees can switch to foraging later in life. The transition from nurse to forager bee showed a relationship to DNA methylation, and the authors found over 150 methylated regions that were different in nurses and foragers.

However, these differences could just be linked to the change from nurse to forager bee, rather than reflecting the differences in behavior between these subcastes. To exclude this possibility, the authors tricked some foragers into reverting back to their nurse roles. This behavioral 'U turn' resulted in DNA methylation patterns that were also mostly reverting, showing a pattern more like that seen in nurse bees than that in foragers.

Credit: Brian Herb and Christofer Bang

These findings suggest that there is a close link between the pattern of DNA methylation and the role of worker bees. More broadly, these results underline that it is not just the DNA sequence that decides how genes modulate behavior and that epigenetic modulation can be a powerful effector of behavioral patterns.