Cinget Benjamin, de Lafontaine Guillaume, Gérardi Sébastien, Bousquet Jean
Canada Research Chair in Forest and Environmental Genomics, Centre for Forest Research and Institute for Systems and Integrative Biology, Université Laval, 1030 Avenue de la Médecine, Québec, QC, Canada, G1V0A6.
Mol Ecol. 2015 Jun;24(11):2856-70. doi: 10.1111/mec.13194. Epub 2015 May 14.
Secondary contact between closely related taxa routinely occurs during postglacial migrations. After initial contact, the location of hybrid zones may shift geographically or remain spatially stable over time in response to various selective pressures or neutral processes. Studying the extent and direction of introgression using markers having contrasted levels of gene flow can help unravel the historical dynamics of hybrid zones. Thanks to their contrasted maternal and paternal inheritance, resulting in different levels of gene flow for mitochondrial and chloroplast DNA (mtDNA and cpDNA), the Pinaceae stand out as a relevant biological model for this purpose. The objective of the study was to assess whether the hybrid zone between Abies balsamea and Abies lasiocarpa (two largely distributed Pinaceae) has moved or remained stable over time by analysing the distribution of cytoplasmic DNA variation as well as published palaeobotanical data. Interspecific gene flow was higher for cpDNA than mtDNA markers; hence, the geographic distribution of mitotypes was more congruent with species distributions than chlorotypes. This genetic signature was contrary to expectations under a moving hybrid zone scenario, as well as empirical observations in other conifers. Genetic evidence for this rare instance of stable hybrid zone was corroborated by the colonization chronology derived from published fossil data, indicating that the two fir species initially came into contact in the area corresponding to the current sympatric zone 11 kyr ago. While an explanatory analysis suggested the putative influence of various environmental factors on the relative abundance of cytoplasmic genome combinations, further research appears necessary to assess the role of both demographic history and selective factors in driving the dynamics of hybrid zones.
亲缘关系较近的类群之间的二次接触在冰期后迁移过程中经常发生。初次接触后，杂交带的位置可能会随地理变化而移动，或者随着时间推移在各种选择压力或中性过程的影响下保持空间稳定。利用具有不同基因流水平的标记物研究基因渗入的程度和方向，有助于揭示杂交带的历史动态。由于松科植物线粒体和叶绿体DNA（mtDNA和cpDNA）具有不同的母系和父系遗传特征，导致基因流水平不同，因此松科植物是进行此项研究的理想生物模型。本研究的目的是通过分析细胞质DNA变异的分布以及已发表的古植物学数据，评估香脂冷杉和大果冷杉（两种分布广泛的松科植物）之间的杂交带随时间推移是移动了还是保持稳定。cpDNA标记的种间基因流高于mtDNA标记；因此，线粒体类型的地理分布比叶绿体类型更符合物种分布。这种遗传特征与移动杂交带模型的预期相反，也与其他针叶树的实证观察结果不符。已发表化石数据得出的定殖年代学证实了这一罕见的稳定杂交带实例的遗传证据，表明这两种冷杉最初在11千年前与当前同域分布区相对应的区域接触。虽然一项解释性分析表明各种环境因素可能对细胞质基因组组合的相对丰度产生影响，但似乎仍需进一步研究以评估种群历史和选择因素在驱动杂交带动态变化中的作用。
