Phylogenetic insights into the diversification of cutting strategies in leaf-cutting ants

Leaf-cutting ants are dominant herbivores in Neotropical ecosystems, yet the evolutionary origins of their cutting preferences remains unresolved. We investigated whether grass-cutting specialization emerged from a single evolutionary innovation or multiple independent origins. We compiled the predominant cutting behavior of each leaf-cutting ant species and classified them as dicot, grass, or grass–dicot cutters. Integrating these data into a time-calibrated phylogenetic framework allowed us to reconstruct the evolutionary history and diversification of leaf-cutting behavior in these ants. Divergence-time analyses date the origin of leaf-cutting ants to the early Miocene, major crown clades diversified during the late Miocene to early Pliocene, a period of increasing climatic seasonality and landscape openness in South America. The evolutionary history of these ants is strongly influenced by large-scale climatic and geological processes, as evidenced by their origin and major diversification events in close association with Miocene–Pliocene environmental changes. Phylogenetic analyses clarify the contrasting diversification dynamics of Acromyrmex , Amoimyrmex and Atta . Acromyrmex traces back to ~15 Ma and is structured into at least four major clades, with a distinct grass cutting clade. In contrast, Atta is a younger lineage characterized by rapid diversification during the Pliocene. Amoimyrmex occupies an early diverging position, indicating an independent origin of grass cutting within the group. Ancestral state reconstructions consistently indicate that dicot cutting is the ancestral condition, with grass and mixed dicot–grass cutting evolving independently multiple times. These repeated transitions coincide with the temporal expansion of open, grass-dominated habitats and likely reflect adaptive responses to new ecological opportunities. The convergent evolution of grass-cutting strategies, despite the mechanical and ecological challenges posed by silica-rich grasses, suggests that cutting preferences are evolutionarily flexible yet functionally constrained traits. Together, our results suggest that grass-cutting is not phylogenetically conserved, but rather represents a recurring adaptive response to environmental change. This highlights how major landscape transformations during the Miocene–Pliocene period promoted repeated ecological innovation in socially complex herbivores.