Luttikhuizen P C, Drent J, Baker A J
Royal Netherlands Institute for Sea Research, Den Burg, The Netherlands.
Mol Ecol. 2003 Aug;12(8):2215-29. doi: 10.1046/j.1365-294x.2003.01872.x.
Mitochondrial DNA sequence data for 295 individuals of the marine bivalve Macoma balthica (L.) were collected from 10 sites across the European distribution, and from Alaska. The data were used to infer population subdivision history and estimate current levels of gene flow. Inferred historical biogeography was expected to be congruent with colonization of the Atlantic Ocean from the Pacific Ocean after the opening of the Bering Strait 3.5 Ma. In addition, the last glacial maximum, about 18000 years ago, was expected to have been responsible for most of the present-day distribution of molecular variation within Europe, because the area must have been recolonized after confinement to France and the south of the British Isles during the last glacial maximum. Current gene flow was hypothesized to be high, because the larvae of M. balthica spend 2-5 weeks drifting in the water column. The geographical distribution of one highly diverged haplotype clade was found to be disjunct and was encountered exclusively in samples from the Baltic Sea and Alaska. A molecular clock calibration for marine bivalve cytochrome-c-oxidase I dates this clade as having split off from the other haplotypes 9.8-39 Ma. Multiple colonizations of the Atlantic Ocean from the Pacific by M. balthica may explain the strong differences found between Baltic Sea and other European populations of this species. The sympatric occurrence of the highly diverged mitochondrial lineages in western parts of the Baltic Sea points to secondary admixture. With the use of coalescent analysis, population divergence times for French vs. other non-Baltic European populations ('Atlantic population assemblage') were estimated at a minimum of about 110000 years ago, well before the last glacial maximum 18000 years ago. Signatures of population divergence of M. balthica that appear to have originated during the Pleistocene have thus survived the last glacial maximum. Some of the populations within the Atlantic assemblage are currently isolated, while others appear to be connected by gene flow. Apparently, populations of this species can remain highly subdivided in spite of the potential for high gene flow, implying that their population and evolutionary dynamics can be independent.
从欧洲分布区的10个地点以及阿拉斯加收集了295个海洋双壳贝类波罗的海蛤仔（Macoma balthica (L.)）个体的线粒体DNA序列数据。这些数据用于推断种群细分历史并估计当前的基因流动水平。推断的历史生物地理学预计与350万年前白令海峡开通后从太平洋对大西洋的殖民情况相符。此外，约18000年前的末次盛冰期预计是造成欧洲境内目前分子变异分布的主要原因，因为在末次盛冰期该区域被限制在法国和不列颠群岛南部后，肯定经历了重新殖民。当前的基因流动被假设为很高，因为波罗的海蛤仔的幼虫会在水柱中漂流2至5周。发现一个高度分化的单倍型分支的地理分布是间断的，且仅在波罗的海和阿拉斯加的样本中出现。对海洋双壳贝类细胞色素c氧化酶I的分子钟校准将该分支与其他单倍型的分化时间定在980万至3900万年前。波罗的海蛤仔从太平洋对大西洋的多次殖民可能解释了该物种波罗的海种群与其他欧洲种群之间存在的巨大差异。在波罗的海西部高度分化的线粒体谱系的同域出现表明存在二次混合。通过使用溯祖分析，法国与其他非波罗的海欧洲种群（“大西洋种群组合”）的种群分化时间估计至少在约11万年前，远早于1万8千年前的末次盛冰期。因此，似乎起源于更新世的波罗的海蛤仔种群分化特征在末次盛冰期后留存了下来。大西洋组合中的一些种群目前是隔离的，而其他种群似乎通过基因流动相连。显然，尽管该物种有高基因流动的潜力，但其种群仍可能高度细分，这意味着它们的种群和进化动态可能是独立的。
