Abstract
Caste determination in social Hymenoptera (whether a female egg develops into a reproductive queen or a sterile worker) is a remarkable example of phenotypic plasticity where females with highly similar genomes exhibit striking differences in morphology and behaviour. This phenotypic dichotomy is typically influenced by environmental factors. However, recent studies have revealed a strong caste-genotype association in hybridogenetic ants: workers are all interlineage hybrids while queens are all purebred, suggesting that female caste fate is genetically determined. Using the hybridogenetic ant Cataglyphis mauritanica, we show that under laboratory conditions, purebred offspring develop into reproductive queens but occasionally give rise to workers. Moreover, while hybrids typically become workers, juvenile hormone treatment can switch their developmental pathway to the reproductive caste. These results indicate that phenotypic plasticity has been retained in an ant with a strong caste-genotype association, despite its lack of expression in natural conditions.