Morrow J, Scott L, Congdon B, Yeates D, Frommer M, Sved J
Fruit Fly Research Centre, School of Biological Sciences, University of Sydney, New South Wales, Australia.
Evolution. 2000 Jun;54(3):899-910. doi: 10.1111/j.0014-3820.2000.tb00090.x.
Two sibling species of tephritid fruit fly, Bactrocera tryoni and B. neohumeralis, occur sympatrically throughout the range of B. neohumeralis in Australia. Isolation between the two species appears to be maintained by a difference in mating time: B. tryoni mates at dusk, whereas B. neohumeralis mates during the middle of the day. A morphological difference in humeral callus color also distinguishes the two species. Despite clear phenotypic evidence that B. tryoni and B. neohumeralis are distinct species, genetic differentiation as measured by four markers--nuclear DNA sequences from the white gene and the ribosomal internal transcribed spacer (ITS2), and mitochondrial DNA sequences from the cytochrome b (cytb) and cytochrome oxidase subunit II (COII) genes--is very small. Minor fixed differences occur in the ITS2 sequence, however, in all other cases the two species exhibit a high level of shared polymorphic variation. The close genetic similarity suggests either that speciation has occurred very rapidly and recently in the absence of any mitochondrial DNA sorting or that the sharing of polymorphisms is due to hybridization or introgression. A third species within the tryoni complex, B. aquilonis, is geographically isolated. Bactrocera aquilonis is also genetically very similar, but in this case there is clear differentiation for the mitochondrial loci. The three species form a group of considerable interest for investigation of speciation mechanisms.
实蝇科果蝇的两个姐妹物种，昆士兰果实蝇（Bactrocera tryoni）和新肩带果实蝇（B. neohumeralis），在澳大利亚新肩带果实蝇的整个分布范围内同域分布。这两个物种之间的隔离似乎是由交配时间的差异维持的：昆士兰果实蝇在黄昏时交配，而新肩带果实蝇在中午交配。肩前骨痂颜色的形态差异也区分了这两个物种。尽管有明确的表型证据表明昆士兰果实蝇和新肩带果实蝇是不同的物种，但通过四个标记测量的遗传分化——来自白色基因和核糖体内部转录间隔区（ITS2）的核DNA序列，以及来自细胞色素b（cytb）和细胞色素氧化酶亚基II（COII）基因的线粒体DNA序列——非常小。然而，ITS2序列中存在微小的固定差异，在所有其他情况下，这两个物种表现出高度的共享多态性变异。紧密的遗传相似性表明，要么物种形成在没有任何线粒体DNA分选的情况下非常迅速且最近才发生，要么多态性的共享是由于杂交或基因渗入。昆士兰果实蝇复合体中的第三个物种，北方果实蝇（B. aquilonis），在地理上是隔离的。北方果实蝇在遗传上也非常相似，但在这种情况下，线粒体基因座有明显的分化。这三个物种形成了一组非常值得研究物种形成机制的对象。
