Department of Biodiversity and Plant Systematics, Centre for Organismal Studies (COS) Heidelberg, Heidelberg University, Heidelberg, Germany.
Global Institute for Food Security, Seed Developmental Biology Program, University of Saskatchewan, Canada.
Ann Bot. 2017 Nov 28;120(6):955-966. doi: 10.1093/aob/mcx110.
In Central Europe Hypericum perforatum and Hypericum maculatum show significant hybridization and introgression as a consequence of Pleistocene range fluctuations, and their gene pools are merging on higher ploidy levels. This paper discusses whether polyploid hybrid gene pools are trapped in the ecological climatic niche space of their diploid ancestors, and tests the idea of geographical parthenogenesis.
DNA sequence information of nuclear ribosomal DNA and plastid loci, ploidy level estimates and ecological niche modelling are used to characterize the various diploid and polyploid gene pools and unravel spatio-temporal patterns of gene flow among them.
On the diploid level, the three gene pools are clearly distinct between and within species of H. perforatum (two gene pools) and H. maculatum, and their divergence dates back to the first half of the Pleistocene. All polyploids in Central Europe show high levels of past and contemporary gene flow between all three gene pools. The correlation of genetic and geographical distances breaks down if the latter is larger than 250 km, indicating recent and ongoing gene flow. The two species are ecologically differentiated, but in particular hybrids among all three gene pools do not show significant niche differences compared to their parental gene pools, except for some combinations with H. maculatum.
Inter- and intraspecific gene flow between inter- and intra-species gene pools is limited on the diploid level, and the geographical distribution of the diploids largely reflects Pleistocene evolutionary history. Secondary contact promoted hybridization and introgression on the polyploid level, enabling offspring to escape the diploid gene pools. However, the hybrid polyploids do not show significant niche differences compared to their diploid progenitors. It is concluded that the observed absence of niche divergence has precluded further differentiation and geographical partitioning of new polyploid lineages being effectively separated from the parental lines. The predominantly apomictic reproducing polyploids are trapped in the polyploid gene pool and the ecological climatic niche space of their diploid ancestors.
在中欧，贯叶金丝桃和贯叶连翘由于更新世范围波动而发生显著的杂交和基因渐渗，它们的基因库在较高的多倍体水平上融合。本文讨论了多倍体杂种基因库是否被困在其二倍体祖先的生态气候生态位空间中，并检验了地理孤雌生殖的观点。
使用核核糖体 DNA 和质体基因座的 DNA 序列信息、倍性水平估计和生态位建模来描述各种二倍体和多倍体基因库，并揭示它们之间基因流的时空模式。
在二倍体水平上，三个基因库在贯叶金丝桃（两个基因库）和贯叶连翘的种间和种内都明显不同，它们的分化可以追溯到更新世的前半段。中欧所有的多倍体都表现出高水平的过去和当代基因流，在所有三个基因库之间。如果后者大于 250 公里，遗传和地理距离的相关性就会破裂，表明最近和正在进行的基因流。这两个物种在生态上是有区别的，但特别是在所有三个基因库中的杂交种与它们的亲本基因库相比，没有明显的生态位差异，除了与贯叶连翘的一些组合。
种间和种内基因库之间的种间和种内基因流在二倍体水平上是有限的，二倍体的地理分布在很大程度上反映了更新世的进化历史。次生接触促进了多倍体水平上的杂交和基因渐渗，使后代能够逃避二倍体基因库。然而，与它们的二倍体祖先相比，杂种多倍体并没有表现出明显的生态位差异。因此，可以得出结论，观察到的生态位差异不存在，阻止了新的多倍体谱系的进一步分化和地理划分，有效地将它们与亲本谱系分离。主要通过无融合生殖繁殖的多倍体被困在多倍体基因库和它们的二倍体祖先的生态气候生态位空间中。
