The rank of an ant in its colony’s caste is now understood to be determined by genetics. Evolutionary biologists at Johannes Gutenberg University Mainz (JGU) have found in a recent study that an ant’s DNA controls not only physical differences, but behavioral ones as well. Within an ant colony, it is genetics that determine an individual’s position rather than other factors such as age or size.
Evolutionary biologists have found this genetic determination of labor to be present in other insect societies as well. In an ant colony, the drastic difference of a member’s behavior is often paired with variations in physical appearance and physiological function. A soldier ant, for example, can weigh up to 100 times more than the brood care workers with whom they share the same genetic background.
A queen ant, which develops drastically different traits from other colony members, such as having a lifespan of up to 30 years compared to only a few, models a system known as polyphenism. Polyphenism describes situations in which the same genotype, or carried genes, produces different phenotypes, or expressed genes. These differences can be observed in behavior, individual morphology and life history.
An ant colony is comprised of a queen and workers, but the workers can be further subdivided into brood-carers, foragers or nest defense ants. A queen is the only actively fertile member of the colony; but if she dies, the brood care workers will develop ovaries and take on the group’s reproductive functions. “Either these worker genes have undergone major modifications or they are novel genes,” according to Barbara Fldmeyer from the JGU Institute of Zoology.
The remarkable ability of the brood-carers to adapt to the changing needs of the colony is the phenomenon that led scientists to induce fertility in brood workers and compare their gene expression with that of other colony members.
Differences between colony members’ genes were greatest between the queen and workers, while there were fewer differences between infertile brood care workers and foragers. While scientists found that genetics are responsible for the division of labor in ants, confusion remains over where some of the genes in newly fertile workers come from. They were not found in other insects unless they represent a highly-modified version of an already identified gene.
These recent findings about insect societies illustrate another dimension of DNA: the importance of epigenetics, or how genes can be modified by environmental factors, as ants with the same genes diverge greatly in phenotypic traits as a direct result of the food larvae they receive during development.
Susanne Foitzik, who is the head of the JGU Evolutionary Biology work group, said that with the major advances being made in the biology field, “We can now also look at a species known for their complexity in social behavior.” Biologists want to further investigate the genes that are responsible for the extremely long life and fertility of insect queens.
This study suggests that from an evolutionary standpoint, social insects with workers are preferred to a solitary insect lifestyle. While it is now clear that genetics are responsible for the division of labor in an ant colony, the mechanisms by which the polyphenism occurs remains to be understood.
By Lara Stielow