Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan, USA.
Department of Botany, National Museum of Natural History, MRC 166, Smithsonian Institution, Washington, District of Columbia, USA.
Mol Ecol. 2022 Jul;31(13):3722-3737. doi: 10.1111/mec.16502. Epub 2022 Jun 6.
The role of hybridization in diversification is complex and may result in many possible outcomes. Not only can hybridization produce new lineages, but those lineages may contain unique combinations of adaptive genetic variation derived from parental taxa that allow hybrid-origin lineages to occupy unique environmental space relative to one (or both) parent(s). We document such a case of hybridization between two sedge species, Carex nova and Carex nelsonii (Cyperaceae), that occupy partially overlapping environmental space in the southern Rocky Mountains, USA. In the region hypothesized to be the origin of the hybrid lineage, one parental taxon (C. nelsonii) is at the edge of its environmental tolerance. Hybrid-origin individuals display mixed ancestry between the parental taxa-of nearly 7000 unlinked loci sampled, almost 30% showed evidence of excess ancestry from one parental lineage-approximately half displayed a genomic background skewed towards one parent, and half skewed towards the other. To test whether excess ancestry loci may have conferred an adaptive advantage to the hybrid-origin lineage, we conducted genotype-environment association analyses on different combinations of loci-with and without excess ancestry-and with multiple contrasts between the hybrids and parental taxa. Loci with skewed ancestry showed significant environmental associations distinguishing the hybrid lineage from one parent (C. nelsonii), whereas loci with relatively equal representation of parental ancestries showed no such environmental associations. Moreover, the overwhelming majority of candidate adaptive loci with respect to environmental gradients also had excess ancestry from a parental lineage, implying these loci have facilitated the persistence of the hybrid lineage in an environment unsuitable to at least one parent.
杂交在物种多样化中的作用非常复杂，可能会产生许多不同的结果。杂交不仅可以产生新的谱系，而且这些谱系可能包含来自双亲的适应性遗传变异的独特组合，使杂交起源的谱系相对于一个（或两个）亲本在独特的环境中占据独特的生态位。我们记录了美国落矶山脉南部的两种莎草物种 Carex nova 和 Carex nelsonii（莎草科）之间的杂交案例，它们占据了部分重叠的环境空间。在假设为杂交谱系起源的地区，一个亲代分类群（C. nelsonii）处于其环境容忍度的边缘。杂交起源的个体在双亲之间表现出混合的祖先背景-在采样的近 7000 个不相关的基因座中，几乎 30%显示出来自一个亲本谱系的过度祖先的证据-大约一半显示出偏向一个亲本的基因组背景，另一半偏向另一个亲本。为了测试多余祖先基因座是否赋予了杂交起源谱系适应优势，我们对不同的基因座组合进行了基因型-环境关联分析-包括具有和不具有多余祖先的基因座，以及杂交种和双亲之间的多个对比。具有倾斜祖先的基因座显示出与一个亲本（C. nelsonii）区分杂交谱系的显著环境关联，而具有相对相等的双亲祖先代表的基因座则没有这种环境关联。此外，绝大多数与环境梯度相关的候选适应性基因座也具有来自一个亲本的多余祖先，这意味着这些基因座促进了杂交谱系在至少一个不适合亲本的环境中的生存。
