Adaptive trade-offs between vertebrate defence and insect predation drive Amazonian ant venom evolution.

Stinging ants have diversified into various ecological niches, and selective pressures may have contributed to shape the composition of their venom. To explore the drivers underlying venom variation in ants, we sampled 15 South American rainforest species and recorded a range of traits, including ecology, morphology and venom bioactivities. Principal component analysis of both morphological and venom bioactivity traits reveals that stinging ants display two functional strategies where species have evolved towards either an exclusively offensive venom or a multi-functional venom. Additionally, phylogenetic comparative analysis indicates that venom function (predatory, defensive or both) and mandible morphology correlate with venom bioactivity and volume. Further analysis of the venom biochemistry of the 15 species revealed switches between cytotoxic and neurotoxic venom compositions among species. Our study supports an evolutionary trade-off between the ability of venom to deter vertebrate predators and to paralyse insect prey which are correlated with different venom compositions and life-history strategies among Formicidae.