Evolution and Regulation of Decoupled Dimorphic Scaling Patterns in Ants

Allometric evolution, changing how morphological traits scale disproportionately to body size, has fuelled adaptive radiations. In ants, allometry has facilitated the repeated evolution of a worker-soldier caste system. Here we reveal an unexpected scaling pattern, and its superorganismal regulation, within the hyperdiverse genus Pheidole. We discovered that antennal sizing between the small worker and the big soldier is identical, lacking inter-caste scaling (antennae-body scaling is decoupled) yet retaining intra-caste scaling. Furthermore, we have pinpointed the evolutionary origin of this decoupling. Finally, manipulations of social environment, developmental hormones, and interorgan signalling influences the modularity-integration of trait-body covariation, uncovering head-to-body decoupling and the production of novel nanosoldiers. Collectively, this challenges our previous understandings of trait covariation, modularity, and their regulation, from individual to society and across species.