Soundscapes and selection: morphology, ecology, and evolutionary dynamics of weberian apparatus in the ictalurid catfish

Abstract

The Weberian apparatus is an innovation serving as the primary sound-conduction path for otophysan fishes. In this study, we investigate how North American catfishes (Ictaluridae) how this system varies across diverse ecological landscapes. By leveraging CT scanning and geometric morphometrics on 136 specimens across 47 species, we mapped the evolutionary trajectories of three critical components: the scaphium, tripus, and peripheral structures including the associated vertebrae and ligament insertions. Our findings challenge conventional expectations that the apparatus is phylogenetically conserved. While phylogenetic signal is significant but low, we discovered exceptionally high morphological disparity driven by ecological selective forces. Factors such as stream velocity, climate, and even body coloration correlate strongly with ossicle shape, reflecting functional adaptations to specific micro-habitats. Crucially, we identified a clear signal of modularity; the scaphium and tripus demonstrate decoupled evolutionary rates, allowing them to evolve independently. This modularity suggests that the Weberian apparatus is not a rigid unit, but a highly plastic system that ictalurids might be used to fine-tune their sensory systems to adapt to ecological pressures.