Kinematics of benthic suction feeding in Callichthyidae and Mochokidae, with functional implications for the evolution of food scraping in catfishes.

Food scraping has independently evolved twice from suction feeding in the evolution of catfishes: within neotropical Loricarioidea and paleotropical Mochokidae. To gain insight in the evolutionary transitions associated with the evolution towards scraping, we analyzed prey capture kinematics in two species of benthic suction feeders which belong to taxa that are closely related to the scraper lineages (respectively, Corydoras splendens and Synodontis multipunctatus), and compared it to prey capture in a more distantly related, generalist suction feeder (Clarias gariepinus). Simultaneous ventral and lateral view high-speed videos were recorded to quantify the movements of the lower jaw, hyoid, pectoral girdle and neurocranium. Additionally, ellipse modeling was applied to relate head shape differences to buccal expansion kinematics. Similarly to what has been observed in scrapers, rotations of the neurocranium are minimal in the benthic suction feeders, and may consequently have facilitated the evolution of a scraping feeding mechanism. The hypothesis that fish with a more laterally compressed head rely more heavily on lateral expansion of the buccal cavity to generate suction, was confirmed in our sample of catfish species. Since an important contribution of lateral expansion of the head to suction may avoid the need for a strong, ventral depression of the mouth floor during feeding, we hypothesized that this may have allowed a closer association with the substrate in the ancestors of scrapers. However, our hypothesis was not supported by an ancestral state reconstruction, which suggests that scraping probably evolved from sub-terminal mouthed ancestors with dorsoventrally flattened heads.