Gentile G, Slotman M, Ketmaier V, Powell J R, Caccone A
Department of Ecology and Evolutionary Biology, Yale University, 165 Prospect St., New Haven, CT 06520-8106, USA.
Insect Mol Biol. 2001 Feb;10(1):25-32. doi: 10.1046/j.1365-2583.2001.00237.x.
Analyses of inversions in polytene chromosomes indicate that, in West Africa, Anopheles gambiae (sensu stricto) may be a complex of more than a single taxonomic unit, and these units have been called chromosomal forms. In order to determine whether this genetic discontinuity extends to the rest of the genome, as would be expected if reproductive isolation exists, we have sequenced several regions of both the nuclear and mitochondrial genomes. With one exception, we were unable to identify any nucleotide sites that differentiate the chromosomal forms. The exception was the internal transcribed spacer (ITS) of the ribosomal DNA (rDNA). Three sites in this region distinguish Mopti chromosomal form from Savanna and Bamako in Mali and Burkina Faso. However, outside these two countries, the association between chromosomal form and rDNA type does not always hold. Together with the variants in the rDNA intergenic spacer (IGS) described in the accompanying papers (della Torre et al., 2001; Favia et al., 2001), we can recognize two major types of rDNA, Type I and Type II (corresponding to molecular forms S and M in della Torre et al., 2001). Type I is widespread in West Africa and is the only type found outside of West Africa (i.e. Tanzania and Madagascar). Type II is confined to West Africa. We were unable to detect any heterozygosity for the ITS types even in five collections containing both types. A sample from the island of São Tomé could not be classified into either Type I or Type II as the rDNA had characteristics of both. In general, our results confirm that An. gambiae is not a single pan-mictic unit, but exactly how to define any new taxa remains problematic. Finally, we have found minor variants of the major rDNA types fixed in local populations; contrary to most previous studies, this suggests restricted gene flow among populations of this species.
对多线染色体倒位的分析表明，在西非，冈比亚按蚊（狭义）可能是一个不止单一分类单元的复合体，这些单元被称为染色体型。为了确定这种遗传间断是否延伸到基因组的其他部分（如果存在生殖隔离，情况应该如此），我们对核基因组和线粒体基因组的几个区域进行了测序。除了一个例外，我们无法识别出任何能区分染色体型的核苷酸位点。这个例外是核糖体DNA（rDNA）的内部转录间隔区（ITS）。该区域的三个位点可将马里和布基纳法索的莫普提染色体型与萨凡纳型和巴马科型区分开来。然而，在这两个国家之外，染色体型与rDNA类型之间的关联并不总是成立。连同随附论文（della Torre等人，2001年；Favia等人，2001年）中描述的rDNA基因间隔区（IGS）的变异，我们可以识别出两种主要的rDNA类型，I型和II型（分别对应于della Torre等人，2001年中的分子型S和M）。I型在西非广泛分布，也是在西非以外地区（即坦桑尼亚和马达加斯加）发现的唯一类型。II型仅限于西非。即使在五个同时包含两种类型的样本中，我们也未能检测到ITS类型的任何杂合性。来自圣多美岛的一个样本无法归类为I型或II型，因为其rDNA具有两者的特征。总体而言，我们的结果证实冈比亚按蚊不是一个单一的随机交配单元，但究竟如何定义任何新的分类群仍然存在问题。最后，我们发现主要rDNA类型的微小变异在当地种群中是固定的；与大多数先前的研究相反，这表明该物种的种群之间基因流动受限。
