Do caecilians face selective pressure from elapid snake predators? A study by Mancuso et al (2023) searched for clues in neurotoxin fighting systems in 37 caecilian species, representing all currently known families of caecilians in the Americas, Africa, and Asia, and the Seychelles. Three types of caecilian resistance neurotoxins were identified. The study demonstrated that resistance to alpha-neurotoxins convergently evolved at least fifteen times across the caecilian tree (three times in Africa, seven times in the Americas, and five times in Asia). In addition, several species were shown to possess multiple resistance modifications acting synergistically, thus they concluded that caecilians must have undergone at least 20 separate events involving the origin of toxin resistance. In contrast, resistance in non-caecilian amphibians was found to have arisen only five separate times. Together, the mutations underlying resistance in caecilians constitute a robust signature of positive selection, which strongly correlates with elapid presence through both space (sympatry with caecilian-eating elapids) and time (Cenozoic radiation of elapids). This study demonstrates the extent of convergent evolution that can be expected when a single widespread predatory adaptation triggers parallel evolutionary arms races at a global scale.

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