Data from: Bird migratory flyways influence the phylogeography of the invasive brine shrimp Artemia franciscana in its native American range

Since Darwin’s time, waterbirds have been considered an important vector for the dispersal of continental aquatic invertebrates. Bird movements have facilitated the worldwide invasion of the American brine shrimp Artemia franciscana, transporting cysts (diapausing eggs), and favouring rapid range expansions from introduction sites. Here we address the impact of bird migratory flyways on the population genetic structure and phylogeography of A. franciscana in its native range in the Americas. We examined the sequence variation for two mitochondrial gene fragments (COI and 16S for a subset of the data) in a large set of population samples representing the entire native range of A. franciscana. Furthermore, we performed Mantel tests and redundancy analyses (RDA) to test the role of flyways, geography and human introductions on the phylogeography and population genetic structure at a continental scale. A. franciscana mitochondrial DNA was very diverse, with two main clades, largely corresponding to Pacific and Atlantic populations, mirroring American bird flyways. There was a high degree of regional endemism, with populations subdivided into at least 12 divergent, geographically restricted and largely allopatric mitochondrial lineages, and high levels of population structure ( Φ ST of 0.92), indicating low ongoing gene flow. We found evidence of human-mediated introductions in nine out of 39 populations analysed. Once these populations were removed, Mantel tests revealed a strong association between genetic variation and geographic distance (i.e., isolation-by-distance pattern). RDA showed that shared bird flyways explained around 20% of the variance in genetic distance between populations and this was highly significant, once geographic distance was controlled for. The variance explained increased to 30% when the factor human introduction was included in the model. Our findings suggest that bird-mediated transport of brine shrimp propagules does not result in substantial ongoing gene flow; instead, it had a significant historical role on the current species phylogeography, facilitating the colonisation of new aquatic environments as they become available along their main migratory flyways.

自达尔文时代以来，水鸟一直被视为大陆水生无脊椎动物扩散的重要媒介（vector）。鸟类的迁徙活动推动了美国卤虫（Artemia franciscana）在全球范围内的入侵——通过携带其孢囊（滞育卵），助力该物种从引入位点快速实现分布范围扩张。本研究旨在探讨鸟类迁徙航线对美洲原生分布区内美国卤虫（A. franciscana）种群遗传结构与系统地理学（phylogeography）的影响。我们针对覆盖该物种全部原生分布区的大量种群样本，对两段线粒体基因片段（COI与16S，仅部分数据集包含16S片段）的序列变异情况进行了检测。此外，我们开展了曼特尔检验（Mantel test）与冗余分析（Redundancy Analysis, RDA），以在大陆尺度下检验迁徙航线、地理因素与人类引种对该物种种群系统地理学格局与遗传结构的作用。美国卤虫的线粒体DNA具有极高的多样性，可划分为两个主要进化枝（clades），大致对应太平洋与大西洋种群，这与美洲鸟类的迁徙航线分布高度契合。该物种存在显著的区域特有性（endemism），种群被细分为至少12个分化显著、地理范围受限且基本呈异域分布的线粒体谱系（lineages），种群遗传分化水平极高（Φ_ST=0.92），表明当前持续进行的基因流（gene flow）水平极低。在本次分析的39个种群中，我们发现9个种群存在人类介导引种的证据。移除这些种群后，曼特尔检验显示遗传变异与地理距离之间存在强关联，即距离-隔离（isolation-by-distance）模式。冗余分析结果表明，在控制地理距离的影响后，共享的鸟类迁徙航线可解释种群间遗传距离约20%的变异，且该结果具有极高的统计学显著性；若将人类引种因素纳入模型，其可解释的变异占比提升至30%。本研究结果显示，鸟类介导的卤虫繁殖体（propagules）传播并未带来显著的当前持续基因流；相反，其在历史层面上对该物种当前的系统地理学格局起到了关键作用，助力卤虫在其主要迁徙航线沿线可利用的新生水生环境中完成定植（colonisation）。