Mukabayire O, Caridi J, Wang X, Touré Y T, Coluzzi M, Besansky N J
Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556-0369, USA.
Insect Mol Biol. 2001 Feb;10(1):33-46. doi: 10.1046/j.1365-2583.2001.00238.x.
Patterns of DNA sequence variation in the ribosomal DNA (rDNA) second internal transcribed spacer (ITS2) and five unlinked single-copy nuclear loci were examined for evidence of reproductive isolation among four chromosomally recognized taxa of Anopheles gambiae from West Africa: Savanna, Bamako, Mopti and Forest, as well as sibling species An. arabiensis and An. merus. Included among the single-copy loci were three sequence-tagged random amplified polymorphic DNA (RAPD) loci, two of which (R15 and R37) had been reported as discriminating between Mopti and other chromosomal forms. Each of the five single-copy sequences were highly polymorphic in most samples. However, the R15 and R37 loci had no diagnostic value, and therefore are not recommended as tools in recognition of field-collected An. gambiae chromosomal forms. Although pairwise comparisons between species generally revealed significant levels of differentiation at all five loci, variation was not partitioned by chromosomal form within An. gambiae at any single-copy locus examined. The few exceptions to these trends appear related to a location either inside or nearby chromosomal inversions. At the tryptophan oxygenase locus inside inversion 2Rb, variation was structured only by inversion orientation and not by taxonomic designation even between An. gambiae and An. arabiensis, providing the first molecular evidence that the 2Rb inversion was transferred between species by introgressive hybridization. By contrast, the rDNA showed fixed differences between species and a difference diagnostic for Mopti, consistent with effective, if not complete, reproductive isolation. The apparent disagreement between the data from this locus and multiple single-copy loci within An. gambiae may be explained by the much lower effective population size of rDNA, owing to concerted evolution, which confers increased sensitivity at much shorter divergence times. Taken together with the accompanying reports by della Torre et al. (2001), Favia et al. (2001) and Gentile et al. (2001), our data suggest that neutral molecular markers may not have the sensitivity required to detect isolation between these recently established taxa.
对核糖体DNA（rDNA）的第二内部转录间隔区（ITS2）以及五个不连锁的单拷贝核基因座中的DNA序列变异模式进行了研究，以寻找来自西非的冈比亚按蚊四个染色体识别分类单元（稀树草原型、巴马科型、莫普提型和森林型）以及近缘种阿拉伯按蚊和梅氏按蚊之间生殖隔离的证据。单拷贝基因座包括三个序列标签随机扩增多态性DNA（RAPD）基因座，其中两个（R15和R37）已被报道可区分莫普提型和其他染色体形式。五个单拷贝序列中的每一个在大多数样本中都具有高度多态性。然而，R15和R37基因座没有诊断价值，因此不建议将其作为识别野外采集的冈比亚按蚊染色体形式的工具。尽管物种间的成对比较通常显示在所有五个基因座上都有显著的分化水平，但在所检查的任何单拷贝基因座上，冈比亚按蚊内部的变异都没有按染色体形式进行划分。这些趋势的少数例外似乎与染色体倒位内部或附近的位置有关。在倒位2Rb内部的色氨酸加氧酶基因座处，变异仅由倒位方向构建，即使在冈比亚按蚊和阿拉伯按蚊之间也不由分类学指定构建，这提供了第一个分子证据，表明2Rb倒位是通过渐渗杂交在物种之间转移的。相比之下，rDNA显示出物种之间的固定差异以及对莫普提型具有诊断性的差异，这与有效的（即使不是完全的）生殖隔离一致。该基因座的数据与冈比亚按蚊内多个单拷贝基因座的数据之间明显的不一致，可能是由于rDNA的有效种群大小低得多，这是由于协同进化导致的，这使得在短得多的分歧时间内具有更高的敏感性。与德拉·托雷等人（2001年）、法维亚等人（2001年）和真蒂莱等人（2001年）的相关报告一起，我们的数据表明，中性分子标记可能没有检测这些最近形成的分类单元之间隔离所需的敏感性。
