Data from: Weaving a tangled web: divergent and reticulate speciation in Boechera fendleri sensu lato (Brassicaceae: Boechereae)

Hybrid speciation is relatively common in plants compared to other well-studied groups. Polyploidy and apomixis are strongly associated with hybrid speciation, presumably due to the opportunities they provide for both reestablishing reproductive function in hybrids with incomplete chromosomal homology and creating rapid reproductive isolation in sympatry. Boechera, a species-rich genus closely related to Arabidopsis, is a particularly fertile ground for the study of hybrid speciation. Thirty-eight apomictic triploid hybrid species are currently recognized in Boechera. Recent research has shown that apomictic diploid hybrids, although very rare in angiosperms, are common in Boechera. Given this complexity, focused studies of individual species complexes are critical to understanding speciation and diagnosing biodiversity in Boechera. Here we analyze DNA sequences from seven nuclear loci and multilocus genotypes from 15 microsatellite markers in a group of closely related taxa formerly included in B. fendleri. Our results support the recognition of four species previously segregated from B. fendleri s. l., including three genetically distinct, sexual diploids (B. fendleri, B. spatifolia, and B. texana) and one apomictic triploid hybrid (B. porphyrea). We also identify four novel apomictic diploid hybrid species (B. carrizozoensis, B. centrifendleri, B. sanluisensis, and B. zephyra) and additional apomictic triploid hybrids. Our results reveal a complex network of relationships. Sexual diploid species can hybridize to form apomictic diploids, and members of these two groups can hybridize to form trigenomic, apomictic triploids.

与其他研究较为深入的类群相比，杂交物种形成（hybrid speciation）在植物中相对常见。多倍体化（polyploidy）与无融合生殖（apomixis）与杂交物种形成存在强关联，推测其原因在于二者可为两类过程提供契机：一是在染色体同源性不完全的杂种中重建生殖功能，二是在同域分布（sympatry）类群中快速建立生殖隔离。弯叶芥属（Boechera）是与拟南芥属（Arabidopsis）亲缘关系紧密的物种丰富类群，是研究杂交物种形成的理想体系。目前该属已确认38个无融合生殖三倍体杂种物种。近期研究表明，尽管无融合生殖二倍体杂种在被子植物中极为罕见，但在弯叶芥属中却较为常见。鉴于该类群的复杂性，针对单个物种复合体的聚焦研究对于理解弯叶芥属的物种形成过程与生物多样性诊断至关重要。本研究对一组曾被归入广义芬德勒弯叶芥（B. fendleri s. l.）的近缘类群，分析了7个核基因座（nuclear loci）的DNA序列以及15个微卫星标记（microsatellite markers）的多位点基因型。研究结果支持将4个曾从广义芬德勒弯叶芥中分出的物种予以正式确认，其中包括3个遗传上独立的有性生殖二倍体物种：芬德勒弯叶芥（B. fendleri）、狭叶弯叶芥（B. spatifolia）以及德克萨斯弯叶芥（B. texana），以及1个无融合生殖三倍体杂种物种：紫花弯叶芥（B. porphyrea）。本研究还鉴定出4个全新的无融合生殖二倍体杂种物种：卡里佐索弯叶芥（B. carrizozoensis）、近缘芬德勒弯叶芥（B. centrifendleri）、圣路易斯弯叶芥（B. sanluisensis）以及西风弯叶芥（B. zephyra），以及额外的无融合生殖三倍体杂种类群。研究结果揭示了一套复杂的亲缘关系网络：有性生殖二倍体物种可通过杂交形成无融合生殖二倍体，而这两类类群的成员又可进一步杂交形成三基因组型的无融合生殖三倍体。