Parchman Thomas L, Buerkle C Alex, Soria-Carrasco Víctor, Benkman Craig W
Department of Biology, University of Nevada Reno, Reno, NV, 89557, USA.
Department of Botany, University of Wyoming, Laramie, WY, 82071, USA.
Mol Ecol. 2016 Nov;25(22):5705-5718. doi: 10.1111/mec.13825. Epub 2016 Sep 29.
Despite substantial interest in coevolution's role in diversification, examples of coevolution contributing to speciation have been elusive. Here, we build upon past studies that have shown both coevolution between South Hills crossbills and lodgepole pine (Pinus contorta), and high levels of reproductive isolation between South Hills crossbills and other ecotypes in the North American red crossbill (Loxia curvirostra) complex. We used genotyping by sequencing to generate population genomic data and applied phylogenetic and population genetic analyses to characterize the genetic structure within and among nine of the ecotypes. Although genome-wide divergence was slight between ecotypes (F = 0.011-0.035), we found evidence of relative genetic differentiation (as measured by F ) between and genetic cohesiveness within many of them. As expected for nomadic and opportunistic breeders, we detected no evidence of isolation by distance. The one sedentary ecotype, the South Hills crossbill, was genetically most distinct because of elevated divergence at a small number of loci rather than pronounced overall genome-wide divergence. These findings suggest that mechanisms related to recent local coevolution between South Hills crossbills and lodgepole pine (e.g. strong resource-based density dependence limiting gene flow) have been associated with genome divergence in the face of gene flow. Our results further characterize a striking example of coevolution driving speciation within perhaps as little as 6000 years.
尽管人们对协同进化在物种多样化中的作用有着浓厚兴趣，但协同进化促成物种形成的例子却难以寻觅。在此，我们以过往研究为基础，这些研究既表明了南山交嘴雀与扭叶松之间存在协同进化，也显示出南山交嘴雀与北美红交嘴雀复合体中的其他生态型之间存在高度的生殖隔离。我们利用测序基因分型来生成群体基因组数据，并应用系统发育和群体遗传学分析来刻画九个生态型内部及之间的遗传结构。尽管生态型之间全基因组的差异较小（F = 0.011 - 0.035），但我们发现许多生态型之间存在相对遗传分化（以F 衡量）以及内部的遗传凝聚性。正如对游牧和机会主义繁殖者的预期，我们未检测到距离隔离的证据。唯一的定居生态型——南山交嘴雀，在遗传上最为独特，这是因为少数位点的差异增加，而非全基因组范围内有明显差异。这些发现表明，南山交嘴雀与扭叶松之间近期局部协同进化相关的机制（例如基于资源的强烈密度依赖限制基因流动）在存在基因流动的情况下与基因组差异有关。我们的结果进一步刻画了一个协同进化可能在短短6000年内推动物种形成的显著例子。
