Phenotypic plasticity and genetic differentiation drive troglomorphic character development in European cave loach

Abstract

Using a cross-fostering experiment, we provide evidence for the contribution of both genetic differentiation and phenotypic plasticity to troglomorphic character development in the recently discovered cave form ofBarbatula barbatula, an evolutionarily young lineage and first cavefish described in Europe, the northernmost record. We established reproducing populations of cave- and surface-dwelling loaches to produce cave, surface, and hybrid offspring and reared the F1 fish in a common garden setting in total darkness (DD) to simulate cave conditions as well as under the natural photoperiod (DL). We observed significant differences in the occurrence and extent of typical troglomorphic target characters among the offspring groups. Regardless of rearing conditions, cave fish exhibited smaller eyes, lighter body coloration, longer barbels, and larger olfactory epithelium than seen in surface fish. Hybrids in both rearing conditions generally showed an intermediate level of these traits. Surface and hybrid DD fish differed from the DL groups, resembling the cave fish phenotype in several traits, including eye size and body pigmentation. In contrast, cave and hybrid DL fish groups resembled surface fish phenotypes. Results confirmed that troglomorphic traits arise from heritable genetic differentiation of cave from surface forms and that phenotypic plasticity contributes to the process of adaptation to novel light conditions.

Unravelling the origins of boldness behaviour: a common garden experiment with cavefish ( Barbatula barbatula )

“…After more than six months of acclimation in the laboratory, we conducted a controlled pairwise breeding experiment whereby we paired fish with cave, surface and mixed origins to establish a laboratory-reared population of fish with different origins (see [ 31 ] for further details). Although breeding was challenging, we were able to obtain a large number of eggs from the different pairs.…”

“…We furthermore classified lenses into four classes to indicate their quality: Class 3 (normal), lens uniform in colour with a diameter approximately half that of the eye; Class 2, lens cloudy or milky, diameter 80–100% of Class 3 lenses; Class 1, lens < 80% the size of Class 3, completely white; and Class 0, no lens detected. Diversification of the complete morphology of cave loaches was the focus of another study and is described in detail there [ 31 ].…”

Unravelling the origins of boldness: A common garden experiment with cave fish (Barbatula barbatula)

“…After more than six months of acclimation in the lab, we conducted a controlled pairwise breeding experiment whereby we paired fish with cave, surface, and mixed origins to establish a laboratory-reared population of fish with different origins (see [33] for further details). Although breeding was challenging, we were able to obtain a large number of eggs from the different pairs.…”

“…We furthermore classified lenses into four classes to indicate their quality: Class 3 (normal), lens uniform in color with a diameter approximately half that of the eye; Class 2, lens cloudy or milky, diameter 80-100% of Class 3 lenses; Class 1, lens < 80 % the size of Class 3, completely white; and Class 0, no lens detected. Diversification of the complete morphology of cave loaches was the focus of another study and is described in detail there [33].…”