Breaking trait scaling via the evolution and regulation of dimorphic decoupling in ants.

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