Plant Evolutionary Ecology, Institute of Evolution and Ecology, University of Tübingen, Auf der Morgenstelle 1, 72076 Tübingen, Germany.
BMC Evol Biol. 2013 May 22;13:102. doi: 10.1186/1471-2148-13-102.
Phylogenetic studies, particularly those based on rDNA sequences from plant roots and basidiomata, have revealed a strikingly high genetic diversity in the Sebacinales. However, the factors determining this genetic diversity at higher and lower taxonomic levels within this order are still unknown. In this study, we analysed patterns of genetic variation within two morphological species, Sebacina epigaea and S. incrustans, based on 340 DNA haplotype sequences of independent genetic markers from the nuclear (ITS + 5.8S + D1/D2, RPB2) and mitochondrial (ATP6) genomes for 98 population samples. By characterising the genetic population structure within these species, we provide insights into species boundaries and the possible factors responsible for genetic diversity at a regional geographic scale.
We found that recombination events are relatively common between natural populations within Sebacina epigaea and S. incrustans, and play a significant role in generating intraspecific genetic diversity. Furthermore, we also found that RPB2 and ATP6 genes display higher levels of intraspecific synonymous polymorphism. Phylogenetic and demographic analyses based on nuclear and mitochondrial loci revealed three distinct phylogenetic lineages within of each of the morphospecies S. epigaea and S. incrustans: one major and widely distributed lineage, and two geographically restricted lineages, respectively. We found almost no differential morphological or ecological characteristics that could be used to discriminate between these lineages.
Our results suggest that recombination and negative selection have played significant roles in generating genetic diversity within these morphological species at small geographical scales. Concordance between gene genealogies identified lineages/cryptic species that have evolved independently for a relatively long period of time. These putative species were not associated with geographic provenance, geographic barrier, host preference or distinct phenotypic innovations.
系统发育研究，特别是基于植物根和担子果 rDNA 序列的研究，揭示了 Sebacinales 中存在极高的遗传多样性。然而，在该目内更高和更低分类水平上决定这种遗传多样性的因素仍然未知。在本研究中，我们基于核基因组（ITS+5.8S+D1/D2、RPB2）和线粒体基因组（ATP6）中 340 个独立遗传标记的 DNA 单倍型序列，对两个形态种 Sebacina epigaea 和 S. incrustans 进行了遗传变异模式分析，共分析了 98 个种群样本。通过对这些物种内遗传种群结构进行特征描述，我们深入了解了种界以及可能导致区域地理尺度上遗传多样性的因素。
我们发现，在 Sebacina epigaea 和 S. incrustans 的自然种群内，重组事件相对频繁，对种内遗传多样性的产生起到了重要作用。此外，我们还发现 RPB2 和 ATP6 基因显示出更高水平的种内同义多态性。基于核和线粒体基因座的系统发育和种群动态分析揭示了形态种 S. epigaea 和 S. incrustans 内的三个不同的系统发育谱系：一个主要的、广泛分布的谱系，以及两个地理上受限的谱系。我们几乎没有发现可以用来区分这些谱系的形态或生态特征上的差异。
我们的研究结果表明，重组和负选择在小地理尺度上对这些形态种内遗传多样性的产生发挥了重要作用。基因谱系之间的一致性鉴定出了已经独立进化了相对较长时间的谱系/隐种。这些假定的种与地理起源、地理屏障、宿主偏好或独特的表型创新无关。
