Gene-Flow in a Mosaic Hybrid Zone: Is Local Introgression Adaptive?
Gene-Flow in a Mosaic Hybrid Zone: Is Local Introgression Adaptive?
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DOI：
10.1534/genetics.114.161380
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发表时间：
2014-07-01
期刊：
影响因子：
3.3
通讯作者：
Bierne, Nicolas
中科院分区：
文献类型：
--
作者：
Fraisse, Christelle;Roux, Camille;Bierne, Nicolas
对杂交类群之间的遗传分化进行全基因组扫描可以识别具有不寻常渗透率的基因组区域。高分化的区域可能代表基因流动的障碍，而低分化的区域可能表明适应性渗透--选择性有益的等位基因在生殖隔离的遗传背景之间的传播。在这里，我们对两个贻贝物种紫贻贝和紫贻贝之间的镶嵌杂交区的不寻常的分化模式进行扫描。一个偏僻的座位Mac-1表现出局部渐渗的特征足迹，在镶嵌带内的一块斑块中，甜菜衍生的等位基因异常频繁，而在镶嵌带外的斑块中，频率很低。进一步的DNA序列分析表明，在这块斑块中，几乎所有的甜菜等位基因多样性都已导入到高山红豆杉的背景中。然后，我们使用各种方法来检验Mac-1存在适应性导入的假设。用最大似然和近似贝叶斯计算方法进行的模拟和模型拟合表明，自适应渗透可以产生“软扫描”，这与我们的数据定性上是一致的。尽管所需的迁移率很高，但这与人口统计学推论所揭示的基因流动的有效障碍的功能是一致的。因此，适应性导入既可以解释Mac-1周围种内分化的减少，也可以解释导入等位基因的高度多样性，尽管也可能调用屏障强度的局部变化。总而言之，我们的结果强调了在解释离群点时需要考虑二次接触的复杂历史。
Genome-wide scans of genetic differentiation between hybridizing taxa can identify genome regions with unusual rates of introgression. Regions of high differentiation might represent barriers to gene flow, while regions of low differentiation might indicate adaptive introgression-the spread of selectively beneficial alleles between reproductively isolated genetic backgrounds. Here we conduct a scan for unusual patterns of differentiation in a mosaic hybrid zone between two mussel species, Mytilus edulis and M. galloprovincialis. One outlying locus, mac-1, showed a characteristic footprint of local introgression, with abnormally high frequency of edulis-derived alleles in a patch of M. galloprovincialis enclosed within the mosaic zone, but low frequencies outside of the zone. Further analysis of DNA sequences showed that almost all of the edulis allelic diversity had introgressed into the M. galloprovincialis background in this patch. We then used a variety of approaches to test the hypothesis that there had been adaptive introgression at mac-1. Simulations and model fitting with maximum-likelihood and approximate Bayesian computation approaches suggested that adaptive introgression could generate a "soft sweep," which was qualitatively consistent with our data. Although the migration rate required was high, it was compatible with the functioning of an effective barrier to gene flow as revealed by demographic inferences. As such, adaptive introgression could explain both the reduced intraspecific differentiation around mac-1 and the high diversity of introgressed alleles, although a localized change in barrier strength may also be invoked. Together, our results emphasize the need to account for the complex history of secondary contacts in interpreting outlier loci.