Genes Determine Caste in Ant Colonies

The development of an ant colony's different castes is influenced by either novel or highly modified genes, evolutionary biologists at Johannes Gutenberg University Mainz (JGU) discovered in a recent study of gene expression.

Ant colonies are largely divided into two groups: the queen and the worker ants. Within the second group, however, there are subdivisions, with tasks varying from foraging and defense, to caring for the brood. In many cases, behavioral specialization is paired with physical differences, such as the queen's ability to live up to 30 years or soldier ants that can weigh up to 100 times more than their peers.

If a queen dies or is removed, brood-care workers will develop their ovaries and start producing offspring. Using this phenomenon to their advantage, the researchers induced fertility in brood-care workers belonging to the ant species Temnothorax longispinosus. They did this in order to compare differences in gene expression tied to major variations in lifespan, fertility and behavior in fertile and infertile workers as well as queens.

Unsurprisingly, the largest discrepancy in gene expression was seen between the queen and her workers. The smallest differences, meanwhile, existed between infertile brood carers and foragers. Fertile brood care workers represented a midway point between the two.

According to the study, while the queens expressed a number of caste-specific genes whose functions were known based on comparisons with other species, the same was not true for workers, for whom about half of the characteristic genes were of unknown function.

"Either these worker genes have undergone major modifications or they are novel genes," Barbara Feldmeyer, from the JGU Institute of Zoology, said in a statement.

"This study of the differences in gene expression among ant castes is characteristic of the enormous advances that are currently being made in the field of biology," said Susanne Foitzik, head of the Evolutionary Biology work group at Mainz University.

"We can now also look at species known for their complexity in social behavior. In addition, by studying ants we can gain insights into the genes that are responsible for the unusually long life and fertility in insect queens," she said.