Repeated convergent evolution of bradykinin mimics as defensive toxins

Natural selection can drive the evolution of similar traits through convergent evolution. Short peptides identical to the vertebrate hormone bradykinin (BK) have been reported from the venoms and skin secretions of certain species of wasps (order Hymenoptera) and frogs (order Anura), respectively. In this study, we demonstrate that the genes encoding the BK-like peptides of hymenopteran venoms and anuran skin secretions do not share common ancestry with that of the vertebrate hormone but instead independently evolved multiple times from peptide toxin genes. These peptides serve a defensive function against vertebrate predators and their resemblance to BK was driven by selection for efficacy at the predators' receptors. Our findings highlight how natural selection can drive repeated convergent evolution of similar molecules across distantly related lineages.