Sensory convergence in the world s largest cavefish diversification: patterns of neuromast evolution, distribution and associated behaviour in Sinocyclocheilus

The genus Sinocyclocheilus represents the largest freshwater cavefish genus in the world. This emerging model system is endemic to the southern Chinese karstic landscape, and demonstrates multiple adaptations for caves (troglomorphism), with eye-degeneration being the most pronounced. The less-apparent lateral line system, which is often expanded in cave-dwellers, has been studied in other cavefish systems, but never in the context of this diversification. Here we investigated the distribution and evolution of cephalic neuromasts in 26 Sinocyclocheilus species. We used live-staining and behavioural assays, and interpreted results in a phylogenetic context. We show that asymmetry in neuromast features and the rate of evolution is greater in cave-adapted species. Ancestral state reconstructions show that most Sinocyclocheilus are right-biased with some scatter, and show convergence of neuromast phenotypes. There is substantial variation in cephalic neuromast distribution patterns between and (to a lesser extent) within species. Behavioural assays show blind species have a distinctive wall-following behaviour. We explain these patterns in the context of the deep evolutionary history associated with this karstic region, other organismal traits, and habitat occupation of these remarkable diversifications of fishes. Interestingly, some of these neuromast patterns and behaviour show convergence with other phylogenetically distant cavefish systems.