Multiple Shifts from Peptide-Based to Metabolite-Based Venoms in Ants
Venom systems are key evolutionary innovations that have contributed to the ecological success of numerous animal lineages. In ants (Formicidae), venom exhibits an exceptional diversity in both chemical composition and delivery mechanisms. Here, we combine a synthesis of current knowledge on the evolution of ant venoms with new phylogenetic comparative analyses, integrating chemical, morphological, and phylogenetic data at the genus level. Comparative analyses across Formicidae support the hypothesis that peptide-rich venoms represent the ancestral condition in ants, as they are widely distributed across basal and derived lineages. Despite this ancestral state, we identify seven independent evolutionary transitions toward non-peptidic venom, occurring in major clades including Dolichoderinae, Formicinae, Stenammini, Solenopsidini, Crematogaster, Pheidole, and fungus-growing ants. Ancestral state reconstruction and tests of correlated evolution across 114 genera show that these seven shifts away from peptide-based venom were almost irreversible and tightly coupled with the loss of stinging capacity and a dietary shift away from predation. These transitions are consistently associated with profound morphological modifications of the venom apparatus, such as reduction or complete loss of the sting, or its transformation into non-injecting structures. Chemically, these systems are dominated by alkaloids, iridoids, formic acid, esters, and terpenoids. These repeated transitions reflect major ecological and evolutionary shifts. Lineages that rely less on individual predation and more on collective foraging or plant-based diets tend to exhibit reduced reliance on injectable peptide toxins. Instead, they favor metabolite-based venoms that can be co-opted from existing biochemical pathways and deployed in diverse ecological contexts. Conversely, peptide-rich venoms are retained in lineages subjected to strong selective pressures for rapid prey immobilization or defense against vertebrate predators. Overall, ants represent a unique model for understanding venom evolution, illustrating how shifts in chemistry, morphology, and ecological strategy can drive repeated and convergent innovations. Future integrative studies combining genomics, metabolomics, and functional assays will be essential to unravel the mechanisms underlying these transitions and their role in the extraordinary diversification of ants.