Table_2_High Genetic Diversity With Weak Phylogeographic Structure of the Invasive Spartina alterniflora (Poaceae) in China.docx

Biological invasion represents a global issue of concern due to its large negative impacts on native ecosystems and society. Elucidating the evolutionary history and genetic basis underpinning invasiveness is critical to understanding how alien species invade and adapt to novel environments. Smooth cordgrass (Spartina alterniflora, 2n = 6x = 62) is a notorious invasive species that causes heavily negative effects on native ecosystems worldwide. Here we addressed the evolutionary mechanisms underlying the invasion and dispersal history of this species along the China coast in the past decades. We employed nine microsatellites and three chloroplast fragments to investigate phylogeographic structure and genetic diversity of 11 native US and 11 invasive Chinese S. alterniflora populations. Demographic history simulation was also performed for both the native and invasive populations, respectively. Comparative genetic analyses of these natural populations revealed that although all the Chinese populations were introduced only once, high level of genetic diversity with weak geographic structure was observed. In particular, both the genetic features and mathematical simulation illustrated very recent population expansion in the Chinese populations. We found that genetic variants identified in native US populations were mixed in the Chinese populations, suggesting the recombination of these original variants during the invasion process. These genetic attributes indicate that Chinese populations might not have experienced a genetic bottleneck during the invasion process. High genetic diversity and genetic admixture might have contributed to the success of invasion of S. alterniflora in China. Our study provides a framework of how the smooth cordgrass spreads along the China coast as well as its potential genetic mechanisms underlying the invasion.

生物入侵因其对本土生态系统与社会造成的严重负面影响，已成为全球备受关注的重大议题。阐明入侵性背后的演化历史与遗传基础，对于理解外来物种如何入侵并适应全新环境至关重要。互花米草（Spartina alterniflora，2n=6x=62）是一种臭名昭著的入侵物种，对全球范围内的本土生态系统均造成极强的负面影响。本研究聚焦于近数十年来该物种在中国沿海的入侵与扩散历史背后的演化机制：我们采用9个微卫星（microsatellite）标记与3个叶绿体片段，对11个美国本土种群与11个中国入侵种群的互花米草开展了系统地理结构与遗传多样性分析；同时分别对本土种群与入侵种群进行了种群历史动态模拟。对这些自然种群的比较遗传学分析显示，尽管所有中国入侵种群均仅经历单次引种事件，但仍呈现出较高的遗传多样性与较弱的地理遗传结构。尤为关键的是，遗传特征与数学模拟结果均表明，中国入侵种群近期发生了快速种群扩张。研究发现，美国本土种群中的遗传变异在入侵种群中发生了混合，暗示这些原始变异在入侵过程中发生了重组。上述遗传特征表明，中国入侵种群在入侵过程中并未经历遗传瓶颈效应。较高的遗传多样性与遗传混合效应，可能是互花米草在中国成功入侵的重要驱动因素。本研究不仅阐明了互花米草在中国沿海的扩散模式，同时揭示了其入侵成功背后的潜在遗传机制。