Kelly David W, Muirhead James R, Heath Daniel D, Macisaac Hugh J
Great Lakes Institute for Environmental Research, University of Windsor, 401 Sunset Avenue, Windsor, Ontario, Canada N9B 3P4.
Mol Ecol. 2006 Oct;15(12):3641-53. doi: 10.1111/j.1365-294X.2006.03012.x.
Biological invasions may combine the genetic effects of population bottlenecks and selection and thus provide valuable insight into the role of such processes during novel environmental colonizations. However, these processes are also influenced by multiple invasions, the number of individuals introduced and the degree of similarity between source and receiving habitats. The amphipod Gammarus tigrinus provides a useful model to assess these factors, as its invasion history has involved major environmental transitions. This species is native to the northwest Atlantic Ocean, although it invaded both brackish and freshwater habitats in the British Isles after introduction more than 65 years ago. It has also spread to similar habitats in Western Europe and, most recently, to Eastern Europe, the Baltic Sea, and the Laurentian Great Lakes. To examine sources of invasion and patterns of genetic change, we sampled populations from 13 native estuaries and 19 invaded sites and sequenced 542 bp of the mitochondrial COI gene. Strong native phylogeographical structure allowed us to unambiguously identify three allopatrically evolved clades (2.3-3.1% divergent) in invading populations, indicative of multiple introductions. The most divergent clades occurred in the British Isles and mainland Europe and were sourced from the St Lawrence and Chesapeake/Delaware Bay estuaries. A third clade was found in the Great Lakes and sourced to the Hudson River estuary. Despite extensive sampling, G. tigrinus did not occur in freshwater at putative source sites. Some European populations showed reduced genetic diversity consistent with bottlenecks, although selection effects cannot be excluded. The habitat distribution of clades in Europe was congruent with the known invasion history of secondary spread from the British Isles. Differences in salinity tolerance among lineages were suggested by patterns of habitat colonization by different native COI clades. Populations consisting of admixtures of the two invading clades were found principally at recently invaded fresh and brackish water sites in Eastern Europe, and were characterized by higher genetic diversity than putative source populations. Further studies are required to determine if these represent novel genotypes. Our results confirm that biological invasions need not result in diminished genetic diversity, particularly if multiple source populations, each with distinctive genetic composition, contribute to the founding populations.
生物入侵可能会结合种群瓶颈和选择的遗传效应，从而为这些过程在新环境定殖过程中的作用提供有价值的见解。然而，这些过程也受到多次入侵、引入个体数量以及源栖息地和接收栖息地之间的相似程度的影响。双栖虾虎鱼（Gammarus tigrinus）提供了一个评估这些因素的有用模型，因为其入侵历史涉及重大的环境转变。该物种原产于西北大西洋，尽管在65多年前被引入后，它入侵了不列颠群岛的咸淡水和淡水栖息地。它还扩散到了西欧的类似栖息地，最近又扩散到了东欧、波罗的海和劳伦琴五大湖。为了研究入侵来源和遗传变化模式，我们从13个原生河口和19个入侵地点采集了样本，并对线粒体COI基因的542 bp进行了测序。强大的原生系统地理结构使我们能够明确识别入侵种群中三个异域进化的分支（分歧度为2.3 - 3.1%），这表明存在多次引入。分歧最大的分支出现在不列颠群岛和欧洲大陆，其来源是圣劳伦斯河和切萨皮克湾/特拉华湾河口。在五大湖发现了第三个分支，其来源是哈得逊河河口。尽管进行了广泛的采样，但在假定的源地点的淡水中并未发现双栖虾虎鱼。一些欧洲种群的遗传多样性降低，这与瓶颈效应一致，不过不能排除选择效应。欧洲各分支的栖息地分布与已知的从不列颠群岛二次扩散的入侵历史相符。不同原生COI分支的栖息地定殖模式表明了各谱系在耐盐性上的差异。由两个入侵分支混合组成的种群主要出现在东欧最近入侵的淡水和咸淡水地点，其遗传多样性高于假定的源种群。需要进一步研究以确定这些是否代表新的基因型。我们的结果证实，生物入侵不一定会导致遗传多样性的减少，特别是如果多个具有独特遗传组成的源种群对奠基种群有贡献的话。
