Data from: No evidence for host specialization or host-race formation in the European bitterling (Rhodeus amarus), a fish that parasitizes freshwater mussels

Coevolutionary relationships between parasites and hosts can elevate the rate of evolutionary changes due to reciprocal adaptations between coevolving partners. Such relationships can result in the evolution of host specificity. Recent methodological advances have permitted the recognition of cryptic lineages, with important consequences for our understanding of biological diversity. We used the European bitterling (Rhodeus amarus), a freshwater fish that parasitizes unionid mussels, to investigate host specialization across regions of recent and ancient sympatry between coevolving partners. We combined genetic data (12 microsatellite and 2 mitochondrial markers) from five populations with experimental data for possible mechanisms of host species recognition (imprinting and conditioning). We found no strong evidence for the existence of cryptic lineages in R. amarus, though a small proportion of variation among individuals in an area of recent bitterling-mussel association was statistically significant in explaining host specificity. No other measures supported the existence of host-specific lineages. Behavioural data revealed a weak effect of conditioning that biased behavioural preferences toward specific host species. Host imprinting had no effect on oviposition behaviour. Overall, we established that populations of R. amarus show limited potential for specialization, manifested as weak effects of host conditioning and genetic within-population structure. Rhodeus amarus is the only species of mussel-parasitizing fish in Europe, which contrasts with the species-rich communities of bitterling in eastern Asia where several host-specific bitterling occur. We discuss costs and constraints on the evolution of host-specific lineages in our study system and more generally.

寄生虫与宿主之间的协同进化关系，可因协同进化伙伴间的互惠适应性提升进化改变速率。此类关系可促成宿主专一性（host specificity）的演化。近年来的方法学进展使得研究者得以识别隐存谱系（cryptic lineages），这对深化生物多样性认知具有重要意义。我们以寄生珠蚌科贻贝（unionid mussels）的淡水鱼类欧洲鳑鲏（Rhodeus amarus）为研究对象，探究协同进化伙伴间新近与长期同域分布区域的宿主特化现象。我们整合了5个种群的遗传数据（12个微卫星标记与2个线粒体标记），以及宿主物种识别潜在机制——印记（imprinting）与条件化（conditioning）的实验数据。研究结果显示，未发现欧洲鳑鲏（R. amarus）存在隐存谱系的有力证据；不过在新近形成鳑鲏-蚌类共生关系的区域中，个体间的少量变异对宿主专一性的解释具有统计学显著性。其余分析均未支持宿主专一性谱系的存在。行为学数据表明，条件化对宿主物种选择偏好存在微弱的偏向性影响，而宿主印记对产卵行为（oviposition behaviour）无显著作用。综上，我们证实欧洲鳑鲏（R. amarus）种群的特化潜力有限，具体表现为宿主条件化效应微弱，且种群内部存在遗传结构。欧洲鳑鲏是欧洲唯一的蚌寄生鱼类，这与东亚地区物种丰富的鳑鲏群落形成鲜明对比——东亚存在多种宿主专一性鳑鲏物种。我们就本研究体系乃至更广范围的宿主专一性谱系演化的成本与限制因素展开了讨论。