Sensory evolution in a cavefish radiation: Patterns of neuromast distribution and associated behaviour in Sinocyclocheilus (Cypriniformes: Cyprinidae)

Sinocyclocheilus, a large radiation of freshwater cavefish, are well-known for their presence of regressive features (e.g., variable eye reduction). Fewer constructive features are known, such as the expansion of the lateral line system (LLS) involved in detecting water movements. The precise relationship between LLS expansion and cave adaptation is not well understood. Here we examine morphological and behavioural features of the LLS in Sinocyclocheilus characterized by broad variation in eye size, habitat and geographic distribution. Using live-staining techniques and automated behavioural analyses, we examined 26 Sinocyclocheilus species and quantified neuromast organ numbers, positions, and laterality within a phylogenetic context. We then examined how these morphological features may relate to wall-following, an established cave-associated behaviour mediated by the lateral line. We show that most species demonstrated laterality (i.e., asymmetry) in neuromast organs on the head, oft...