Gentile Gabriele, Della Torre Alessandra, Maegga Bertha, Powell Jeffrey R, Caccone Adalgisa
Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut 06520-8106, USA.
Genetics. 2002 Aug;161(4):1561-78. doi: 10.1093/genetics/161.4.1561.
Of the seven recognized species of the Anopheles gambiae complex, A. gambiae s.s. is the most widespread and most important vector of malaria. It is becoming clear that, in parts of West Africa, this nominal species is not a single panmictic unit. We found that the internal transcribed spacer (ITS) of the X-linked rDNA has two distinct sequences with three fixed nucleotide differences; we detected no heterozygotes at these three sites, even in areas of sympatry of the two ITS types. The intergenic spacer (IGS) of this region also displays two distinct sequences that are in almost complete linkage disequilibrium with the distinct ITS alleles. We have designated these two types as S/type I and M/type II. These rDNA types correspond at least partly to the previously recognized chromosomal forms. Here we expand the geographic range of sampling to 251 individuals from 38 populations. Outside of West Africa, a single rDNA type, S/type I, corresponds to the Savanna chromosomal form. In West Africa, both types are often found in a single local sample. To understand if these findings might be due to unusual behavior of the rDNA region, we sequenced the same region for 46 A. arabiensis, a sympatric sibling species. No such distinct discontinuity was observed for this species. Autosomal inversions in one chromosome arm (2R), an insecticide resistance gene on 2L, and this single X-linked region indicate at least two genetically differentiated subpopulations of A. gambiae. Yet, rather extensive studies of other regions of the genome have failed to reveal genetic discontinuity. Evidently, incomplete genetic isolation exists within this single nominal species.
在冈比亚按蚊复合体的七个已确认物种中，冈比亚按蚊指名亚种是分布最广且最重要的疟疾传播媒介。越来越明显的是，在西非部分地区，这个名义上的物种并非单一的随机交配群体。我们发现，X连锁核糖体DNA的内转录间隔区（ITS）有两个不同的序列，存在三个固定的核苷酸差异；即使在两种ITS类型同域分布的区域，我们在这三个位点也未检测到杂合子。该区域的基因间隔区（IGS）也显示出两个不同的序列，它们与不同的ITS等位基因几乎完全处于连锁不平衡状态。我们将这两种类型分别命名为S/ I型和M/ II型。这些核糖体DNA类型至少部分对应于先前确认的染色体形式。在这里，我们将采样的地理范围扩大到来自38个种群的251个个体。在西非以外地区，单一的核糖体DNA类型S/ I型对应于稀树草原染色体形式。在西非，两种类型常常在单个本地样本中被发现。为了了解这些发现是否可能归因于核糖体DNA区域的异常行为，我们对46只同域分布的近缘物种阿拉伯按蚊的同一区域进行了测序。该物种未观察到这种明显的间断情况。一条染色体臂（2R）上的常染色体倒位、2L上的一个抗杀虫剂基因以及这个单一的X连锁区域表明冈比亚按蚊至少有两个遗传分化的亚种群。然而，对基因组其他区域进行的相当广泛的研究未能揭示遗传间断情况。显然，在这个单一的名义物种内存在不完全的遗传隔离。
