DOI: 10.5061/dryad.fbg79cp2w
title: Genetic differentiation and phenotypic plasticity drive troglomorphic character development in European cavefish

description: 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 groups reared in
 complete darkness, suggesting phenotypic plasticity. Our findings offer
 valuable insights into the interplay between genetic differentiation and
 phenotypic plasticity to troglomorphic adaption. This contributes to the
 broader understanding of the early stages of adaptation, where phenotypic
 plasticity, drift, and selection shape phenotypes. Relatively recently
 established cavefish, such as the Aach cave loach, are promising
 candidates for comparative research investigating evolutionary mechanisms.
description: # 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 distance between the anterior and the posterior nostrils on one side
 of the fish . All length measurements were recorded to the nearest µm.
 Using the lateral images, lenses were categorized into one of four classes
 to indicate quality: Class 3 (normal), featuring a uniformly cloudy lens
 with a circular shape approximately half the diameter of the eye; Class 2,
 characterized by an  inconsistently cloudy or milky lens with a diameter
 ranging from 80 to 100 % of Class 3 lenses; Class 1, where the lens is
 less than 80 % of the size of Class 3 and appears milky or completely
 white; and Class 0, indicating no lens detected. Images of anesthetized
 fish were examined to compare pigmentation via grey-scale analysis. The
 image was opened in ImageJ, and a representative rectangular area between
 the pelvic fin and the beginning of the dorsal fin selected. A score was
 obtained using the grey-scale measurement tool, which provides a number
 from 0 (black) to 254,000 (white). The dataset also contains
 size-corrected measurements for some selected morphometric data. Size
 effects were removed with a normalization equation that considers each
 origin group separately by calculating a unique regression coefficient for
 each group (Reist 1985; Chan and Lee Grismer 2021).. ## Description of the
 data and file structure Each row corresponds to an individual. Individuals
 are assigned to several groups (Origin, Treatment, Family). Information on
 the hatching date and age of the fish is also provided. The morphometric
 data is arranged in columns. The column headings refer to the morphometric
 measurement. Label code: Each individual has a unique identification
 number. Origin codes: Cave = cave stone loach offspring, Rdz = Offspring
 of surface stone loach from the Radolfzeller Aach River, Do = Offspring of
 surface stone loach from the Danube River Treatment codes: DD = complete
 absence of light, DL = natural light:dark cycle Family codes: These refer
 to the Origin and are numbered ## References Reist, J. D. 1985. An
 empirical evaluation of several univariate methods that adjust for size
 variation in morphometric data. Can. J. Zool. 63:1429–1439. Chan, K. O.,
 and L. Lee Grismer. 2021. Correcting for Body Size Variation in
 Morphometric Analysis. bioRxiv 1–16.