Caste Differentiation in Ants

Scientists from the University of Copenhagen have revealed how a specific hormone regulates ant caste differentiation by phenotypic measurements of organ-level developmental changes and matching transcriptome analyses. Published in Proceedings of the National Academy of Sciences of the United States of America (PNAS) on November 4th, 2024, the study entitled "Juvenile hormone as a key regulator for asymmetric caste differentiation in ants" significantly enhances our understandings of caste development and evolution.

Most ants have two morphologically differentiated adult castes - queens and workers - each irreversibly specialized for either reproduction or nonreproductive altruism such as foraging, defense and care of maternal brood. Adult gynes (virgin queens) normally have higher body mass, wings and frontal eyes, as well as enlarged ovaries and a sperm storage organ. In contrast, workers are wingless females with smaller body size and degenerated reproductive tracts, usually without a sperm storage organ. In 1910, the American entomologist William Morton Wheeler noted in his monograph Ants that the superorganismal colonies of ants are strikingly analogous to metazoan bodies because queen and workers function as germline and soma at a higher level of bodily organization: the colony-level.

We are very used to the idea that germline cells in an animal body are set aside for their special reproductive roles very shortly after an egg is fertilized and starts to develop into an embryo. In most social insects with distinct queen (colony germline) and worker (colony soma) castes the analogous developmental differentiation happens in the larval stage and can still be hormonally reversed. However, in some ants colony germlines are also determined earlier, in the embryonic (egg) stage, begging the question whether that makes somatization of workers as irreversible as somatization of animal body cells as development proceeds.

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