Tegelström Håkan, Gelter Hans P
Department of Genetics, Uppsala University, Box 7003, S-750 07, Uppsala, SWEDEN.
Evolution. 1990 Dec;44(8):2012-2021. doi: 10.1111/j.1558-5646.1990.tb04307.x.
The collared flycatcher (Ficedula albicollis) and the pied flycatcher (F. hypoleuca) hybridize where their geographic ranges overlap. Restriction fragment comparison of 5% of the mitochondrial genome showed a sequence divergence of 10% between these flycatcher species. This degree of sequence divergence between a closely related pair of bird species is unusually high and contrasts with the low level of divergence between F. albicollis and F. hypoleuca in nuclear genes (Nei's D = 0.0006) revealed by enzyme electrophoresis. The low nuclear differentiation is explained by sex biassed gene flow and introgression in nuclear genes (via fertile male hybrids), while the high mitochondrial DNA sequence divergence is preserved by sterility of female hybrids, which prevents mitochondrial introgression. This pattern is in accordance with Haldane's rule and is supported by field data on hybrid fertility. The high mtDNA differentiation could be explained by transfer of mitochondrial DNA from a third species during a past period of hybridization.
白领姬鹟（Ficedula albicollis）和斑姬鹟（F. hypoleuca）在其地理分布范围重叠的区域杂交。对线粒体基因组5%的限制性片段进行比较显示，这两种姬鹟之间的序列差异为10%。在亲缘关系较近的一对鸟类物种之间，这种程度的序列差异异常高，与酶电泳显示的白领姬鹟和斑姬鹟在核基因中的低水平差异（内氏遗传距离D = 0.0006）形成对比。核基因低分化现象可通过性别偏向的基因流和核基因渗入（通过可育雄性杂种）来解释，而高线粒体DNA序列差异则因雌性杂种不育得以保留，这阻止了线粒体基因渗入。这种模式符合霍尔丹法则，并得到了关于杂种育性的野外数据支持。高线粒体DNA分化现象可以用过去杂交时期来自第三个物种的线粒体DNA转移来解释。
