Genetic analysis of a recently established Undaria pinnatifida (Laminariales: Alariaceae) population in the northern Wadden Sea reveals close proximity between drifting thalli and the attached population

Undaria pinnatifida, a kelp species native to East Asia, has become cosmopolitan and drawn increasing attention due to its worldwide spread in recent decades. Floating fragments of this alga were found washed ashore on Sylt in 2016, the first record of this species in Germany. Thalli attached to local oyster reefs were detected in 2017. The genetic relationship between the floating and attached thalli on Sylt, as well as their relevance to the populations from northern Europe and native regions, was hitherto unknown. Here, 10 microsatellite markers were used to assess relationships between the recently established population on Sylt and five other northern European populations in France (Brittany, West English Channel), the Netherlands and England (Plymouth, West English Channel) plus three natural populations in China. Almost no genetic differentiation was detected between the floating and attached populations on Sylt, but they were genetically distinct from all the other studied northern European populations. The very low genetic diversity revealed in the new founder populations of Sylt suggests that they came from genetically similar parents. The marked reduction in both the number of alleles and heterozygosity in the northern European populations, as compared with the Chinese ones, is typical of founder effects in recently populated regions. Prominent genetic divergence was found between most of the northern European populations except those within Brittany and Sylt. Further studies will focus on identifying the putative source populations that might be found on shellfish farms, in local marinas or the benthic habitats around Sylt Island.

裙带菜（Undaria pinnatifida）是一种原产于东亚的褐藻物种，近几十年来因在全球范围内广泛扩散而成为广布物种，日益受到学界关注。2016年，科研人员在德国叙尔特岛（Sylt）的岸滩上发现了该藻类的漂浮碎片，这是该物种在德国的首次记录。2017年，又在当地牡蛎礁上发现了附着生长的藻体。此前，学界对叙尔特岛漂浮藻体与附着藻体之间的遗传关系，以及它们与北欧种群及原产地种群的关联尚不明确。本研究采用10个微卫星标记（microsatellite markers），对叙尔特岛新近建立的种群，以及另外5个北欧种群——涵盖法国布列塔尼（英吉利海峡西部）、荷兰与英格兰普利茅斯（英吉利海峡西部）的种群，外加3个中国原生种群——之间的遗传关系进行了评估。研究结果显示，叙尔特岛的漂浮种群与附着种群之间几乎未检测到遗传分化，但二者与所有其他被研究的北欧种群均存在显著遗传差异。叙尔特岛新近建立的奠基种群所展现出的极低遗传多样性，暗示其来源种群的遗传背景较为相似。与中国原生种群相比，北欧种群的等位基因数量与杂合度均显著降低，这是新近拓殖区域奠基者效应的典型特征。除布列塔尼与叙尔特岛的种群外，多数北欧种群之间均存在显著的遗传分化。后续研究将聚焦于识别可能存在于叙尔特岛周边贝类养殖场、当地游艇码头及底栖生境中的潜在来源种群。