Roe Amanda D, Sperling Felix A H
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9.
Mol Ecol. 2007 Sep;16(17):3617-33. doi: 10.1111/j.1365-294X.2007.03412.x.
Accurate delimitation of species boundaries is especially important in cryptic taxa where one or more character sources are uninformative or are in conflict. Rather than relying on a single marker to delimit species, integrative taxonomy uses multiple lines of evidence such as molecular, morphological, behavioural and geographic characters to test species limits. We examine the effectiveness of this approach by testing the delimitation of two cryptic Nearctic species of Dioryctria (Lepidoptera: Pyralidae) using three independent molecular markers [cytochrome c oxidase I (COI), second internal transcribed spacer unit (ITS2), and elongation factor 1alpha (EF1alpha)], forewing variation and larval host plant association. Although mitochondrial DNA (mtDNA) haplotypes do not form reciprocally monophyletic clades, restricted gene flow between COI haplotype groups, and concordance with ITS2 genotypes, forewing variation and host plant associations support delimitation of two Nearctic species: eastern Dioryctria reniculelloides and western Dioryctria pseudotsugella. Conversely, EF1alpha genotype variation was incongruent with the two previous markers. A case of discordance between COI and ITS2 was detected, suggesting either introgression due to hybridization or retained ancestral polymorphism due to incomplete coalescence. This study is consistent with other similar literature where molecular loci in closely related species progress from shared to fixed haplotypes/alleles, and from polyphyletic to reciprocally monophyletic relationships, although loci may vary in these characteristics despite maintenance of genomic integrity between distinct species. In particular, mtDNA in other studies generally showed a lower rate of fixation of differences than did X-linked or autosomal loci, reinforcing the need to use an integrative approach for delimiting species.
在隐性类群中，准确界定物种边界尤为重要，因为在这些类群中，一个或多个特征来源无法提供信息或相互冲突。综合分类学并非依赖单一标记来界定物种，而是使用多条证据线，如分子、形态、行为和地理特征，来检验物种界限。我们通过使用三个独立的分子标记[细胞色素c氧化酶I（COI）、第二内部转录间隔区（ITS2）和延伸因子1α（EF1α）]、前翅变异和幼虫寄主植物关联，来测试北美两种隐性的Dioryctria（鳞翅目：螟蛾科）物种的界定，以此检验这种方法的有效性。尽管线粒体DNA（mtDNA）单倍型并未形成相互单系的分支，但COI单倍型组之间有限的基因流，以及与ITS2基因型、前翅变异和寄主植物关联的一致性，支持将北美两种物种界定为：东部的Dioryctria reniculelloides和西部的Dioryctria pseudotsugella。相反，EF1α基因型变异与前两个标记不一致。检测到一个COI和ITS2之间不一致的案例，这表明可能是由于杂交导致的基因渗入，或者是由于不完全合并而保留的祖先多态性。这项研究与其他类似文献一致，即密切相关物种中的分子位点从共享单倍型/等位基因发展到固定单倍型/等位基因，从多系关系发展到相互单系关系，尽管尽管不同物种之间保持基因组完整性，但位点在这些特征上可能会有所不同。特别是，其他研究中的mtDNA通常显示出比X连锁或常染色体位点更低的差异固定率，这进一步强调了使用综合方法来界定物种的必要性。
