de Lafontaine Guillaume, Bousquet Jean
Canada Research Chair in Forest Genomics Centre for Forest Research and Institute of Systems and Integrative Biology Université Laval Québec QC Canada.
Department of Plant Biology University of Illinois Urbana IL USA.
Ecol Evol. 2017 Apr 22;7(11):3883-3893. doi: 10.1002/ece3.2682. eCollection 2017 Jun.
Assessing directional bias in interspecific gene flow might be important in determining the evolutionary trajectory of closely related species pairs. Using a set of 300 single nucleotide polymorphisms (SNPs) having variable propensity to cross species boundary, we evaluated the genomic extent and direction of interspecific gene flow in a progenitor-derivative spruce species pair (black spruce and red spruce). A higher rate of gene flow was found from black spruce toward red spruce purebreds than vice versa. This asymmetry could reflect the historical gene flow between the two taxa at the time of species inception and during postglacial colonization. A clear asymmetry in introgression was depicted by a greater gene flow between red spruce and hybrids than between black spruce and hybrids. While backcrossing toward red spruce was invariably high across the genome, the actual species boundary is between hybrids and black spruce where gene flow is impeded at those genomic regions impermeable to introgression. Associations between hybrid index and climatic variables (total annual precipitation and mean annual temperature) were tested, as these might indicate a role for exogenous selection in maintaining the species boundary. While an apparent association was found between the hybrid index and precipitation, it collapsed when considered in light of the directional bias in interspecific gene flow. Hence, considering asymmetrical patterns of introgression allowed us to falsify an apparent role for exogenous selection. Although this was not formerly tested here, we suggest that this pattern could result from asymmetrical endogenous selection, a contention that deserves further investigations.
评估种间基因流中的方向偏差对于确定近缘物种对的进化轨迹可能很重要。我们使用一组300个具有不同跨物种边界倾向的单核苷酸多态性（SNP），评估了一个祖先 - 衍生云杉物种对（黑云杉和红云杉）种间基因流的基因组范围和方向。发现从黑云杉到红云杉纯种的基因流速率高于相反方向。这种不对称可能反映了在物种形成时以及冰期后殖民化期间两个分类群之间的历史基因流。红云杉与杂种之间的基因流大于黑云杉与杂种之间的基因流，描绘出了明显的渐渗不对称。虽然向红云杉的回交在整个基因组中始终很高，但实际的物种边界存在于杂种与黑云杉之间，在那些无法进行渐渗的基因组区域，基因流受到阻碍。测试了杂种指数与气候变量（年总降水量和年平均温度）之间的关联，因为这些可能表明外源选择在维持物种边界方面的作用。虽然在杂种指数与降水量之间发现了明显的关联，但考虑到种间基因流中的方向偏差时，这种关联就不成立了。因此，考虑渐渗的不对称模式使我们能够证伪外源选择的明显作用。虽然这里以前没有对此进行测试，但我们认为这种模式可能是由不对称的内源选择导致的，这一观点值得进一步研究。
