Genetic differentiation and phenotypic plasticity drive troglomorphic character development in European cavefish

The Aach cave loach (Barbatula barbatula), a recently discovered member of the Nemacheilidae family, offers a unique opportunity to understand the mechanisms underlying evolutionary change. In a common garden experiment, we reared groups of laboratory-bred cave, surface, and hybrid loach under different light conditions. Troglomorphic characters varied significantly among the fish, influenced to a different extent by parental origin and light conditions. Cavefish progeny consistently exhibited smaller eyes, lighter pigmentation, longer barbels, and larger olfactory epithelia than surface fish, while hybrids displayed intermediate characteristics. Surface and hybrid fish raised in complete darkness resembled the cavefish phenotype, while cavefish raised under a natural photoperiod approached the surface form. Characters associated with eye degeneration were found to be primarily heritable. Conversely, traits related to chemo- and mechano-reception were enhanced in the surface and hybrid ..., , , # Genetic differentiation and phenotypic plasticity drive troglomorphic character development in European cavefish To gain insight into the early environmental adaptation process of the Aach cave loach and its underlying mechanisms, we reared cave, surface, and hybrid offspring in a common garden under either cave (complete absence of light, DD) or surface conditions (natural light:dark cycle, DL). The dataset contains morphometric data of 94 fish from the DD and 93 from the DL treatment group, encompassing all origins. Measurements were extracted from photographs of formalin-fixed fish using ImageJ. Lateral images were used to measure the eye and lens diameter, as well as the length of the second barbel. Dorsal images were used to determine head length and the size of the olfactory epithelium. Head length was measured from the tip of the snout to the posterior margin of the neurocranium . The olfactory epithelium size (longest axis) of the olfactory epithelium was measured as the di...