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 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.

阿赫洞穴鳅（Barbatula barbatula）是鳅科（Nemacheilidae）近年新发现的物种，为解析演化变化的内在机制提供了独特契机。在本项同质园实验（common garden experiment）中，我们将实验室繁育的洞穴型、地表型及杂交型鳅类群组置于不同光照条件下饲养。穴居适应性形态特征（troglomorphic characters）在所有受试鳅类间存在显著差异，且受亲本来源与光照条件的影响程度各不相同。洞穴鳅子代相较地表鳅，始终表现出更小的眼径、更浅的体色、更长的触须以及更发达的嗅觉上皮；而杂交个体则呈现出中间型表型特征。完全黑暗环境下饲养的地表鳅与杂交鳅，其表型趋近于洞穴鳅；而在自然光照周期下饲养的洞穴鳅，则趋近于地表鳅的形态。与眼部退化相关的特征主要为可遗传性状。反之，在完全黑暗环境下饲养的地表鳅与杂交鳅群组中，化学感应与机械感应相关的性状得到增强，这提示存在表型可塑性（phenotypic plasticity）。本研究结果为理解遗传分化与表型可塑性在穴居适应性形态形成中的相互作用提供了重要见解。这有助于进一步深化对适应早期阶段的认知——在该阶段，表型可塑性、遗传漂变与自然选择共同塑造生物表型。诸如阿赫洞穴鳅这类较晚定居洞穴的鳅类，是探究演化机制的比较研究中极具潜力的研究对象。