Biology Department, Utah State University, 5305 Old Main Hill, Logan, UT, 84322, USA.
Ecology Center, Utah State University, 5205 Old Main Hill, Logan, UT, 84322, USA.
BMC Evol Biol. 2018 Apr 25;18(1):61. doi: 10.1186/s12862-018-1173-6.
Hybridization is very common in plants, and the incorporation of new alleles into existing lineages (i.e. admixture) can blur species boundaries. However, admixture also has the potential to increase standing genetic variation. With new sequencing methods, we can now study admixture and reproductive isolation at a much finer scale than in the past. The genus Boechera is an extraordinary example of admixture, with over 400 hybrid derivates of varying ploidy levels. Yet, few studies have assessed admixture in this genus on a genomic scale.
In this study, we used Genotyping-by-Sequencing (GBS) to clarify the evolution of the Boechera puberula clade, whose six members are scattered across the western United States. We further assessed patterns of admixture and reproductive isolation within the group, including two additional species (B. stricta and B. retrofracta) that are widespread across North America. Based on 14,815 common genetic variants, we found evidence for some cases of hybridization. We find evidence of both recent and more ancient admixture, and that levels of admixture vary across species.
We present evidence for a monophyletic origin of the B. puberula group, and a split of B. puberula into two subspecies. Further, when inferring reproductive isolation on the basis of presence and absence of admixture, we found that the accumulation of reproductive isolation between species does not seem to occur linearly with time since divergence in this system. We discuss our results in the context of sexuality and asexuality in Boechera.
杂交在植物中非常普遍，新等位基因的掺入（即混合）会模糊物种界限。然而，混合也有可能增加遗传变异。随着新测序方法的出现，我们现在可以比过去更精细地研究混合和生殖隔离。Boechera 属是混合的一个极好的例子，有超过 400 种不同倍性水平的杂交衍生种。然而，很少有研究在基因组水平上评估这个属的混合。
在这项研究中，我们使用基于测序的基因型（GBS）来阐明 Boechera puberula 进化枝的进化，其六个成员分布在美国西部。我们进一步评估了该组内混合和生殖隔离的模式，包括两个分布在北美的其他物种（B. stricta 和 B. retrofracta）。基于 14815 个常见的遗传变异，我们发现了一些杂交的证据。我们发现了近期和更古老的混合的证据，并且混合的水平在物种之间有所不同。
我们提出了 B. puberula 组的单系起源和 B. puberula 分为两个亚种的证据。此外，当根据混合的有无来推断生殖隔离时，我们发现，在这个系统中，物种之间生殖隔离的积累似乎没有随时间的推移而线性发生。我们在 Boechera 的有性和无性繁殖的背景下讨论了我们的结果。
