Evolutionary innovation of functional fused molariform pharyngeal jaws in suckermouth catfishes

Adaptive radiations are facilitated by innovations that enable ecological specialization and the exploitation of new niches. In the radiation of cichlid fishes, the ability to diversify pharyngeal jaw structures has been proposed as one such innovation, providing ecological opportunities through novel feeding strategies. However, the relevance of pharyngeal innovations in granting access to new ecological resources in other species-rich fish radiations has remained un-clear, including in the radiation of Neotropical suckermouth catfishes in the family Loricariidae. Here, we used computed tomography scans to quantify jaw morphology of 65 species from 57 loricariid genera. These scans enabled us to characterize a wide morphological disparity in both oral and pharyngeal jaw anatomy, including a group with fused lower pharyngeal jaws and molariform pharyngeal teeth that are strikingly similar to those of durophagous cichlid fishes. Using phylogenetic comparative methods, we identified a significant association between both oral jaw morphology and diet, and pharyngeal morphology and diet, suggesting that both sets of jaws can promote ecological specialization. This approach enabled us to identify a significant association between pharyngeal and jaw morphology, indicative of functional integration between the two traits. Finally, experimental feeding trials showed that these catfish species with fused pharyngeal jaws and associated molariform teeth were capable of consuming freshwater molluscs. Collectively, the results support a role for pharyngeal anatomical diversification in the adaptive radiation of loricariid catfishes. They also provide evidence of convergent anatomical innovation between two of the largest freshwater fish adaptive radiations—cichlids and loricariids—that diverged over 220 million years ago.