Daguin C, Bonhomme F, Borsa P
Laboratoire Génome Populations Interactions and IRD, UMR 5000 CNRS, Station Méditerranéenne de l'Environnement Littoral, 1 Quai de la Daurade, 34200 Sète, France.
Heredity (Edinb). 2001 Mar;86(Pt 3):342-54. doi: 10.1046/j.1365-2540.2001.00832.x.
Intron-size variation at the actin gene locus mac-1 was used to characterize mussel, Mytilus spp., populations in the approximately 2000-km wide zone of contact and hybridization ('hybrid zone') between M. edulis and M. galloprovincialis in western Europe. Twenty-five samples were collected in 1995-99 in locations within the hybrid zone and from reference populations of each species. We used correspondence analysis on the matrix of allelic frequencies to determine which alleles are characteristic of each species, and to characterize samples along the genetic gradient between M. edulis and M. galloprovincialis. In the hybrid zone, some samples exhibited mac-1 allele frequencies that were typical of M. edulis; other samples were distributed along the M. edulis/M. galloprovincialis gradient and displayed variable levels of intergradation that were not correlated with geography. Some of the latter samples exhibited significant heterozygote deficiencies. The simple admixture hypothesis (Wahlund effect) could not be rejected for two-fifths of the samples. The hybrid zone thus appeared as a mosaic of populations which are either pure M. edulis, or hybrid between M. galloprovincialis and M. edulis, or a mixture of the foregoing with M. galloprovincialis individuals. These results were consistent with published allozyme data, suggesting that they can be extended to the entire nuclear genome. M. edulis mac-1 alleles were present at moderate frequency in Atlantic M. galloprovincialis, and at significantly lower frequency in some Mediterranean samples. This pattern was homogeneous over a broad geographical range within each basin. It was not evident that introgression of M. edulis into M. galloprovincialis presently occurs south of the zone of contact. We propose that the distinctness of the Atlantic M. galloprovincialis population results from past introgression by M. edulis alleles.
利用肌动蛋白基因位点mac - 1的内含子大小变异来表征贻贝（紫贻贝属）种群，该种群位于西欧紫贻贝和加利福尼亚贻贝之间约2000公里宽的接触和杂交区域（“杂交区”）。1995 - 1999年在杂交区内的地点以及从每个物种的参考种群中采集了25个样本。我们对等位基因频率矩阵进行对应分析，以确定每个物种的特征等位基因，并沿着紫贻贝和加利福尼亚贻贝之间的遗传梯度对样本进行表征。在杂交区内，一些样本呈现出典型的紫贻贝mac - 1等位基因频率；其他样本则沿着紫贻贝/加利福尼亚贻贝梯度分布，并表现出不同程度的渐渗，且与地理因素无关。后一类样本中的一些表现出显著的杂合子缺失。对于五分之二的样本，简单混合假说（瓦隆德效应）无法被拒绝。因此，杂交区呈现出由纯紫贻贝种群、加利福尼亚贻贝和紫贻贝之间的杂交种群，或上述种群与加利福尼亚贻贝个体的混合种群组成的镶嵌体。这些结果与已发表的同工酶数据一致，表明它们可以推广到整个核基因组。紫贻贝的mac - 1等位基因在大西洋加利福尼亚贻贝中以中等频率存在，而在一些地中海样本中频率显著较低。这种模式在每个海域的广泛地理范围内是一致的。目前在接触区以南未发现紫贻贝基因渗入加利福尼亚贻贝的明显迹象。我们认为大西洋加利福尼亚贻贝种群的独特性是过去紫贻贝等位基因渗入的结果。
