Phenotypic Plasticity, Not Supergenes, Explains Diversity in Reproductive Morphologies and Behavioural Strategies in the Ant Hypoponera opacior

Social insects frequently exhibit extensive intraspecific variation in reproductive strategies, characterised by pronounced differences in morphology, physiology, and behaviour. In many ant species, such variation is governed by supergenes that control complex traits, including queen number, size, morphology, and wing development of reproductives. This contrasts with the genetic basis of queen-worker caste differentiation, which typically results from phenotypic plasticity. Here, we investigate the genetic basis of sexual dimorphism in the ant Hypoponera opacior, which produces both winged and ergatoid morphs in males and queens, each associated with distinct reproductive behaviours, potential, and seasonal activity. Using whole-genome resequencing of all morphs, we tested for signatures of supergene architecture. Our analyses revealed no evidence for a supergene or other large scale genetic differentiation underlying this morphological and behavioural diversity. These findings suggest that male and queen morph determination in H. opacior is not controlled by a single genomic region but may instead result from phenotypic plasticity, environmentally sensitive developmental switches, or polygenic factors. Our study demonstrates that complex social traits in ants can evolve and persist without supergene architectures and underscores the importance of considering alternative genetic and epigenetic mechanisms underlying reproductive polymorphisms.