Piccinali Romina, Aguadé Montserrat, Hasson Esteban
Departamento de Ecología, Genética y Evolución, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Buenos Aires, Argentina.
Mol Biol Evol. 2004 Jan;21(1):141-52. doi: 10.1093/molbev/msh006. Epub 2003 Oct 31.
The Xdh (rosy) gene is one of the best studied in the Drosophila genus from an evolutionary viewpoint. Here we analyze nucleotide variation in a 1875-bp fragment of the second exon of Xdh in Argentinian populations of the cactophilic D. buzzatii and its sibling D. koepferae. The major electrophoretic alleles of D. buzzatii not only lack diagnostic amino acids in the region studied but also differ on average from each other by four to 13 amino acid changes. Our data also suggest that D. buzzatii populations belonging to different phytogeographic regions are not genetically differentiated, whereas D. koepferae exhibits a significant pattern of population structure. The Xdh region studied is twice as polymorphic in D. buzzatii as in D. koepferae. Differences in historical population size or in recombinational environment between species could account for the differences in the level of nucleotide variation. In both species, the Xdh region exhibits a great number of singletons, which significantly departs from the frequency spectrum expected under neutrality for nonsynonymous sites and also for synonymous sites in D. buzzatii. These excesses of singletons could be the signature of a recent population expansion in D. buzzatii, whereas they may be simply explained as the result of negative selection in D. koepferae.
从进化的角度来看，Xdh（rosy）基因是果蝇属中研究得最为深入的基因之一。在此，我们分析了嗜仙人掌果蝇D. buzzatii及其近缘种D. koepferae的阿根廷种群中Xdh基因第二外显子1875bp片段的核苷酸变异情况。D. buzzatii的主要电泳等位基因不仅在所研究区域缺乏诊断性氨基酸，而且平均彼此之间存在4到13个氨基酸的差异。我们的数据还表明，属于不同植物地理区域的D. buzzatii种群没有遗传分化，而D. koepferae则呈现出显著的种群结构模式。所研究的Xdh区域在D. buzzatii中的多态性是D. koepferae中的两倍。物种之间历史种群大小或重组环境的差异可能解释了核苷酸变异水平的差异。在这两个物种中，Xdh区域都表现出大量的单例，这与非同义位点以及D. buzzatii同义位点在中性条件下预期的频率谱有显著差异。这些过量的单例可能是D. buzzatii近期种群扩张的标志，而在D. koepferae中，它们可能仅仅是负选择的结果。
