Meirmans P G, Godbout J, Lamothe M, Thompson S L, Isabel N
Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands.
Laurentian Forestry Centre, Canadian Forest Service, Natural Resources Canada, Québec, QC, Canada.
J Evol Biol. 2017 Nov;30(11):2044-2058. doi: 10.1111/jeb.13174. Epub 2017 Sep 30.
Hybridization between species is known to greatly affect their genetic diversity and, therefore, their evolution. Also, within species, there may be genetic clusters between which gene flow is limited, which may impact natural selection. However, few studies have looked simultaneously at the influence of among-species and within-species gene flow. Here, we study the influence of hybridization between Populus balsamifera and Populus trichocarpa on population structure and adaptation in P. balsamifera. We did this by sampling a total of 1517 individuals from across the ranges of these two species, and by genotyping them using a combination of 93 nuclear and 17 cpDNA SNPs. We found that hybridization is mostly limited to the contact zone where the species' distributions overlap. Within P. balsamifera, we found multiple levels of population structure. Interestingly, the border between the Eastern and Central clusters is very sharp, whereas the border between the Central and Western clusters is diffuse. Outlier analysis revealed that three loci associated with the sharp border were also associated with climate. We hypothesize that the observed clusters derive from three refugia during the Pleistocene ice ages. Between the Central and Western clusters, post-glacial long-distance gene flow has led to the diffusion of their border. In the Eastern cluster, we hypothesize that endogenous genomic barriers have developed, leading to the sharp border and a spurious climate association. We conclude that the large-scale genetic structure of P. balsamifera is mostly shaped by historical factors and the influence of interspecific hybridization is limited.
已知物种间的杂交会极大地影响其遗传多样性，进而影响其进化。此外，在物种内部，可能存在基因流受限的基因簇，这可能会影响自然选择。然而，很少有研究同时考察物种间和物种内基因流的影响。在此，我们研究了香脂杨（Populus balsamifera）和毛果杨（Populus trichocarpa）之间的杂交对香脂杨种群结构和适应性的影响。我们通过从这两个物种的分布范围内总共采集1517个个体，并使用93个核单核苷酸多态性（SNP）和17个叶绿体DNA SNP的组合对它们进行基因分型来实现这一目的。我们发现杂交大多局限于两个物种分布重叠的接触区。在香脂杨内部，我们发现了多个层次的种群结构。有趣的是，东部和中部基因簇之间的边界非常清晰，而中部和西部基因簇之间的边界则较为模糊。异常值分析表明，与清晰边界相关的三个基因座也与气候相关。我们推测，观察到的基因簇源自更新世冰期的三个避难所。在中部和西部基因簇之间，冰期后的长距离基因流导致了它们边界的扩散。在东部基因簇中，我们推测内源性基因组屏障已经形成，导致了清晰的边界和虚假的气候关联。我们得出结论，香脂杨的大规模遗传结构主要由历史因素塑造，种间杂交的影响有限。
