Evolutionary simplification and functional shifts of the ant stinger

Morphological evolution reflects a balance between the emergence of novel traits and the reduction or loss of existing traits, and both of these processes shape the diversity of life. Trait simplification, which involves the reduction or loss of structures, is a common phenomenon that provides adaptive advantages in novel ecological contexts. In this study, we examined the evolutionary dynamics and morphological outcomes of the reduction and simplification of the stinging apparatus in ants to elucidate the effect of these changes on broader evolutionary trajectories. Using a phylogenetically informed sampling of 98 ant genera, we explored how stinger morphology evolved in conjunction with behavioural and ecological changes, employing linear morphometrics and phylogenetic comparative methods. Our results revealed that transitions from piercing to nonpiercing stingers were substantially associated with dietary diversification and shifts in foraging strategies, thus reflecting the evolutionary compromises between defense, predation, and ecological specialization. Piercing stingers promoted predatory efficiency and ecological specialization, while nonpiercing stingers imparted behavioural and dietary versatility, such as herbivory and cooperative foraging. These findings highlight that morphological simplification is a key adaptive mechanism in driving ecological transitions and diversification and promoting evolutionary innovation.