Department of Agricultural Sciences, University of Helsinki, Helsinki, Finland.
PLoS One. 2013 Apr 19;8(4):e58073. doi: 10.1371/journal.pone.0058073. Print 2013.
Non-indigenous species (NIS) are species living outside their historic or native range. Invasive NIS often cause severe environmental impacts, and may have large economical and social consequences. Elodea (Hydrocharitaceae) is a New World genus with at least five submerged aquatic angiosperm species living in fresh water environments. Our aim was to survey the geographical distribution of cpDNA haplotypes within the native and introduced ranges of invasive aquatic weeds Elodea canadensis and E. nuttallii and to reconstruct the spreading histories of these invasive species. In order to reveal informative chloroplast (cp) genome regions for phylogeographic analyses, we compared the plastid sequences of native and introduced individuals of E. canadensis. In total, we found 235 variable sites (186 SNPs, 47 indels and two inversions) between the two plastid sequences consisting of 112,193 bp and developed primers flanking the most variable genomic areas. These 29 primer pairs were used to compare the level and pattern of intraspecific variation within E. canadensis to interspecific variation between E. canadensis and E. nuttallii. Nine potentially informative primer pairs were used to analyze the phylogeographic structure of both Elodea species, based on 70 E. canadensis and 25 E. nuttallii individuals covering native and introduced distributions. On the whole, the level of variation between the two Elodea species was 53% higher than that within E. canadensis. In our phylogeographic analysis, only a single haplotype was found in the introduced range in both species. These haplotypes H1 (E. canadensis) and A (E. nuttallii) were also widespread in the native range, covering the majority of native populations analyzed. Therefore, we were not able to identify either the geographic origin of the introduced populations or test the hypothesis of single versus multiple introductions. The divergence between E. canadensis haplotypes was surprisingly high, and future research may clarify mechanisms that structure native E. canadensis populations.
外来物种（NIS）是指生活在其历史或原生范围之外的物种。入侵的 NIS 通常会对环境造成严重影响，并可能产生巨大的经济和社会影响。Elodea（Hydrocharitaceae）是一个新世界属，至少有五个水生被子植物物种生活在淡水环境中。我们的目的是调查入侵水生杂草 Elodea canadensis 和 E. nuttallii 的原生和引入范围的 cpDNA 单倍型的地理分布，并重建这些入侵物种的传播历史。为了揭示用于系统地理学分析的信息丰富的叶绿体（cp）基因组区域，我们比较了原生和引入的 E. canadensis 个体的质体序列。总共，我们在由 112193bp 组成的两个质体序列之间发现了 235 个可变位点（186 个 SNP、47 个插入和两个倒位），并开发了侧翼最可变基因组区域的引物。这些 29 对引物用于比较 E. canadensis 内的种内变异水平和模式与 E. canadensis 和 E. nuttallii 之间的种间变异。基于 70 个 E. canadensis 和 25 个 E. nuttallii 个体的分析，9 对潜在的信息引物对两种 Elodea 物种的系统地理学结构进行了分析，这些个体覆盖了原生和引入的分布。总的来说，两种 Elodea 物种之间的变异水平比 E. canadensis 内的变异水平高 53%。在我们的系统地理学分析中，在两个物种的引入范围中都只发现了一个单倍型。这些单倍型 H1（E. canadensis）和 A（E. nuttallii）在原生范围中也广泛分布，覆盖了分析的大多数原生种群。因此，我们无法确定引入种群的地理起源，也无法检验单一或多个引入的假设。E. canadensis 单倍型之间的差异出人意料地高，未来的研究可能会阐明构成原生 E. canadensis 种群的机制。
