Switching roles within the hive is reflected in reversible epigenetic changes.
All honeybees (Apis mellifera) are born equal, but this situation doesn’t last long. Although genetically identical, the bees soon take on the specific roles of queen or worker. These roles are defined not just by behavioural differences, but by physical ones. Underlying them are minor modifications to their DNA: ‘epigenetic’ changes that leave the DNA sequence intact, but that add chemical tags in the form of methyl (CH3) molecules to sections of the DNA. This in turn alters the way a gene is expressed.
Once a bee is a queen or worker, they fulfil that role for life — the change is irreversible. But that is not the case for the subdivisions among the workers. The workers start out as nurses, which look after and feed the queen and larvae, and most then go on to become foragers, which travel out from the hive in search of pollen. Again the two types have very different methylation patterns in their DNA. This time, however, as the latest research show, the DNA modifications are reversible: if a forager reverts to being a nurse, its methylation pattern reverts too.
Led by Andrew Feinberg of Johns Hopkins University in Baltimore, Maryland, and Gro Amdam of Arizona State University in Tempe, the researchers coaxed forager bees back into nursing roles by removing all the nurses from the hive while the foragers were out looking for pollen. When the foragers returned, they noticed the lack of nurses, and about half of them took on nursing roles. Examination of the methylation patterns in DNA from their brain cells showed that these too had switched back to the pattern associated with nurses.