Phenotypic plasticity plays a major role in the evolution of eusociality in insects. In ants, caste differentiation typically occurs only in females and results in distinct phenotypes, known as castes. Male ants, unlike their female counterparts, are generally monomorphic and contribute solely to reproduction during the mating flight. However, in some exceptional cases, a new caste known as ‘ergatoid male’ – worker-like male – emerges in some ant species. This phenomenon presents an opportunity for us to explore caste differentiation through phenotypic plasticity in ants. In the present study, our objective is to investigate if the molecular mechanisms that govern the formation of different adult female castes are similarly employed in the formation of ergatoid male adults.
We used Technomyrmex albipes as a model and performed RNA-seq on 12 young pupae samples, representing four distinct castes: winged queen, wingless female (intercaste/worker), winged male, and ergatoid male. The results revealed that differential gene expression predominantly occurs between sexes (male vs. female), with a specific subset of genes associated with the development of wingless adults in both sexes. Initially, we identified a number of genes with higher expression levels exclusively in the ergatoid males. However, most of these genes are already known for their roles in insect development. Subsequently, we examined whether genes displaying a winged-wingless differential expression pattern in females also exhibit a similar pattern in males. The results indicated a consistent expression pattern, where genes upregulated or downregulated in wingless females exhibited a corresponding expression trend in ergatoid males. Furthermore, gene ontology analysis of genes with high correlation in winged/wingless-related expression patterns across sexes is reported. These findings suggest that the formation of ergatoid male during the pupal stage in Technomyrmex primarily shares the molecular background with that of wingless female.