Kelly David W, MacIsaac Hugh J, Heath Daniel D
Great Lakes Institute for Environmental Research, University of Windsor, Ontario N9B 3P4, Canada.
Evolution. 2006 Feb;60(2):257-67.
Vicariance and dispersal can strongly influence population genetic structure and allopatric speciation, but their importance in the origin of marine biodiversity is unresolved. In transitional estuarine environments, habitat discreteness and dispersal barriers could enhance divergence and provide insight to evolutionary mechanisms underlying marine and freshwater biodiversity. We examined this by assessing phylogeographic structure in the widespread amphipod Gammarus tigrinus across 13 estuaries spanning its northwest Atlantic range from Quebec to Florida. Mitochondrial cytochrome c oxidase I and nuclear internal transcribed spacer 1 phylogenies supported deep genetic structure consistent with Pliocene separation and cryptic northern and southern species. This break occurred across the Virginian-Carolinian coastal biogeographic zone, where an oceanographic discontinuity may restrict gene flow. Ten estuarine populations of the northern species occurred in four distinct clades, supportive of Pleistocene separation. Glaciation effects on genetic structure of estuarine populations are largely unknown, but analysis of molecular variance (AMOVA) supported a phylogeographic break among clades in formerly glaciated versus nonglaciated areas across Cape Cod, Massachusetts. This finding was concordant with patterns in other coastal species, though there was no significant relationship between latitude and genetic diversity. This supports Pleistocene vicariance events and divergence of clades in different northern glacial refugia. AMOVA results and private haplotypes in most populations support an allopatric distribution across estuaries. Clade mixture zones are consistent with historical colonization and human-mediated transfer. An isolation-by-distance model of divergence was detected after we excluded a suspected invasive haplotype in the St. Lawrence estuary. The occurrence of cryptic species and divergent population structure support limited dispersal, dispersed habitat distribution, and historical factors as important determinants of estuarine speciation and diversification.
地理隔离和扩散会强烈影响种群遗传结构和异域物种形成，但其在海洋生物多样性起源中的重要性仍未得到解决。在过渡性河口环境中，栖息地的离散性和扩散障碍可能会加剧分化，并为海洋和淡水生物多样性的进化机制提供见解。我们通过评估广泛分布于从魁北克到佛罗里达的西北大西洋范围内13个河口的普通钩虾（Gammarus tigrinus）的系统发育地理结构来研究这一问题。线粒体细胞色素c氧化酶I和核糖体DNA内转录间隔区1的系统发育支持了与上新世分离以及隐秘的北方和南方物种相一致的深度遗传结构。这种分化发生在弗吉尼亚 - 卡罗来纳沿海生物地理区，那里的海洋学不连续可能会限制基因流动。北方物种的10个河口种群出现在四个不同的分支中，这支持了更新世的分离。冰川作用对河口种群遗传结构的影响在很大程度上尚不清楚，但分子方差分析（AMOVA）支持了马萨诸塞州科德角以前冰川覆盖区和非冰川覆盖区各分支之间的系统发育地理分化。这一发现与其他沿海物种的模式一致，尽管纬度与遗传多样性之间没有显著关系。这支持了更新世的地理隔离事件以及不同北方冰川避难所中各分支的分化。AMOVA结果和大多数种群中的私有单倍型支持了河口间的异域分布。分支混合区与历史殖民和人类介导的转移一致。在排除了圣劳伦斯河口一个疑似入侵单倍型后，检测到了距离隔离分化模型。隐秘物种的出现和不同的种群结构支持有限的扩散、分散的栖息地分布以及历史因素是河口物种形成和多样化的重要决定因素。
