Pronounced genetic separation among varieties of the Primula cusickiana species complex, a Great Basin endemic

Distinguishing between populations with strong genetic structure and
unique species is a common challenge in systematics, especially for taxa
occurring in fragmented habitats where allopatric speciation may be
widespread and distinct groups may be morphologically similar. Such is
often the case with species complexes across sky island environments. In
these scenarios, biogeography may help to explain the taxonomic relations
between species complex members, and restriction site-associated DNA (RAD)
sequencing methods are commonly used to compare closely related species
across thousands of loci. Here we use RADseq to clarify the boundaries
separating the geographically distinct but morphologically similar
varieties of the Primula cusickiana species complex, and to contextualize
past findings of strong genetic structure among populations within
varieties. Our genetic analyses demonstrate pronounced separation between
isolated populations of this Great Basin endemic, indicating that the
current varietal classification of complex members is inaccurate, and
emphasizing their conservation importance. We discuss how these results
correspond to recent biogeographical models used to describe the
distribution of other sky island taxa in western North America. Our
findings also fit into a wider trend observed for alpine Primula species
complexes, and we consider how edaphic specialization and heterostylous
breeding systems may be contributing to frequent diversification via
allopatric speciation in this genus.

区分具有强烈遗传结构的种群与独特物种，是分类学（systematics）中常见的研究难题，尤其针对分布于碎片化生境的类群（taxa）而言——此类生境中异域成种（allopatric speciation）现象可能广泛存在，且不同类群的形态特征往往极为相似。跨天空岛（sky island）生境的物种复合体（species complex）便常面临此类困境。在此类研究场景中，生物地理学（biogeography）可用于阐明物种复合体各成员间的分类学关系；而限制性酶切位点相关DNA（restriction site-associated DNA, RAD）测序技术，常被用于在数千个基因座（loci）层面比较亲缘关系紧密的物种。本研究借助RADseq技术，厘清了Cusick报春（Primula cusickiana）物种复合体中地理分布迥异但形态相似的变种间的分类界限，并为既往关于变种内种群间强烈遗传结构的研究结果提供了背景阐释。我们的遗传分析结果显示，这一北美大盆地特有种（Great Basin endemic）的隔离种群间存在显著遗传分化，表明当前该物种复合体成员的变种分类体系并不准确，同时凸显了其保护价值。我们还讨论了本研究结果与近年用于阐释北美西部其他天空岛类群分布的生物地理学模型的契合性。本研究结果同样契合高山报春花属（Primula）物种复合体的普遍演化趋势，我们进一步探讨了土壤特化（edaphic specialization）与花柱异长（heterostylous）繁育系统，如何推动该属通过异域成种频繁发生物种分化。