Department of Molecular and Cell Biology, Evolutionary Biology Group (GIBE), Universidade da Coruña, A Zapateira s/n, E-15071 La Coruña, Spain.
Genome. 2010 Jan;53(1):23-34. doi: 10.1139/g09-080.
Internal transcribed spacer 1 and 2 (ITS1 and ITS2) sequences were analysed in Ensis razor shells (Mollusca: Bivalvia: Pharidae). We aimed to (1) test ITS1 and ITS2 as molecular markers at the population level in the successful alien E. directus (Conrad, 1843); (2) test these spacers at the species level in E. directus and three other Ensis species, E. siliqua (L., 1758), E. macha (Molina, 1782), and E. magnus (Schumacher, 1817); and (3) analyse the evolutionary processes that may be shaping Ensis ITS1 and ITS2 extant variation. In E. directus, despite the intragenomic divergence detected, ITS1 and ITS2 were informative in differentiating the geographic areas considered (Denmark and Canada) by means of both the insertion-deletion polymorphism and the nucleotide polymorphism. In this species, the 5.8S ribosomal gene (5.8S) showed scarce polymorphism. At the species level, maximum parsimony and maximum likelihood analyses revealed that ITS1 and ITS2 may be suitable to reconstruct Ensis phylogenetic relationships. Finally, the evolutionary models that best fit the long-term evolution of Ensis ITS1-5.8S-ITS2 are discussed. A mixed process of concerted evolution, birth-and-death evolution, and selection is chosen as an option that may reconcile the long-term evolution of Ensis ITS1-5.8S-ITS2 and 5S ribosomal DNA.
内转录间隔区 1 和 2（ITS1 和 ITS2）序列在贻贝科（软体动物：双壳类：贻贝科）中的剃刀贻贝中进行了分析。我们的目的是：（1）在成功的外来物种 E. directus（Conrad，1843）中，在种群水平上测试 ITS1 和 ITS2 作为分子标记；（2）在 E. directus 和其他三种贻贝物种 E. siliqua（L.，1758）、E. macha（Molina，1782）和 E. magnus（Schumacher，1817）中，在物种水平上测试这些间隔物；（3）分析可能影响贻贝 ITS1 和 ITS2 现存变异的进化过程。在 E. directus 中，尽管检测到了基因组内的差异，但 ITS1 和 ITS2 可以通过插入缺失多态性和核苷酸多态性来区分所考虑的地理区域（丹麦和加拿大），具有信息性。在该物种中，5.8S 核糖体基因（5.8S）显示出很少的多态性。在物种水平上，最大简约法和最大似然法分析表明，ITS1 和 ITS2 可能适合重建贻贝的系统发育关系。最后，讨论了最适合贻贝 ITS1-5.8S-ITS2 长期进化的进化模型。选择协同进化、生死进化和选择的混合过程作为一种可能的选择，以协调贻贝 ITS1-5.8S-ITS2 和 5S 核糖体 DNA 的长期进化。
