Social status determined by genetics

Imagine a corporation in which the CEO expresses one set of genes and assembly line workers express a completely different set of genes. All employees are born with the same genetic composition, but the genes they express determine their labor role, status in the corporation and quality of life. If the CEO passes away, assembly line workers can adapt to express the “CEO-specific genes” in hopes of assuming the role of CEO.

It turns out ant colonies operate in a manner analogous to the way this hypothetical corporation operates. Led by evolutionary biologist Barbara Feldmeyer, researchers at the Institute of Zoology of the Johannes Gutenberg University Mainz in Germany found that in Temnothorax longispinosus, a small species of black ant, females with the same genetic background could differentiate into either queen ants or worker ants, which differ in morphology, behavior and even life expectancy. Like many of their fellow insects in the order Hymenoptera, including wasps and honeybees, T. longispinosus live in colonies with a distinct societal caste system and a clear division of labor. The researchers discovered that although the queen is normally the only individual in the colony that reproduces, if the queen is absent, young brood-tending worker ants often develop ovaries, engage in dominance interactions and become reproductively active within a few weeks.

To study the genetic differentiation and phenotypic plasticity between queen and worker ants, Feldmeyer and her team of researchers experimentally induced the reproductive potential of female worker ants. To set up their experiment, the researchers first categorized the worker ants in their colony as either foragers or brood-carers, based on what activities each ant engaged in during the majority of the time. Work task specialization is age-dependent, as young female workers typically tended the brood while older female workers typically performed foraging duties. The experimenters removed the queen ant from the colony and observed the fertility status of the young brood-carers, who now had the potential to become reproductively active and lay eggs, thus leaping over caste boundaries and transforming into queen ants.

To determine the fertility status of the brood-carers, the ants were frozen to death at sub-zero temperatures before their ovaries were removed and dissected. The condition of the ovaries determined the fertility status of the workers. “Fertile” brood-carers were those with developed ovaries and eggs, while “unfertile” brood-carers were those with short, undeveloped ovaries and no eggs. Following reproductive status assessment, genomic analyses were performed on the DNA of queen ants and the three castes of female worker ants — fertile brood-carers, unfertile brood-carers and foragers — to determine the similarities and differences in gene expression among members of these ant social castes.

Genomic studies revealed clear differences in gene expression among the four female castes, signifying the presence of caste-specific genes in T. longispinosus. Additionally, while foragers and infertile brood-carers had similar gene expression patterns, their expression patterns differed greatly from those of fertile brood-carers and queens. Compared with the expression patterns of foragers and unfertile brood-carers, the expression patterns of fertile brood-carers resembled those of queen ants much more closely. Furthermore, genetic analyses revealed that queen ants possessed far more differentially-expressed genes than any of the three worker castes; in other words, in terms of gene expression, queen ants are far more different from all worker ants than worker ants in different castes are from one another. This indicates that in order for brood-carer ants to become queen ants, either their genes have to undergo major modifications or there are novel genes present. This opens up a new door for tremendous advances in the fields of evolutionary and behavioral biology.

For humans, modifying our genes and altering our gene expression to obtain upward social mobility is neither practical nor ethical. But if ants can bypass the strict caste system of their insect societies and ascend the social pyramid from the bottom to the very top, perhaps humans today ought to reevaluate the structure of their global society, which reserves a life of wealth and privilege to a minuscule minority of its members while confining the masses of its population to a life of poverty and oppression.