School of Biological Sciences, University of Nebraska, Lincoln, Nebraska, 68588.
Current Address: Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, Kansas, 66045.
Evolution. 2015 Jun;69(6):1375-1389. doi: 10.1111/evo.12666. Epub 2015 May 8.
Polyploidy has played an important role in angiosperm diversification, but how polyploidy contributes to reproductive isolation remains poorly understood. Most work has focused on postzygotic reproductive barriers, and the influence of ploidy differences on prezygotic barriers is understudied. To address these gaps, we quantified hybrid occurrence, interspecific self-compatibility differences, and the contributions of multiple pre- and postzygotic barriers to reproductive isolation between diploid Erythronium mesochoreum (Liliaceae) and its tetraploid congener Erythronium albidum. Reproductive isolation between the study species was nearly complete, and naturally occurring hybrids were infrequent and largely sterile. Although postzygotic barriers effected substantial reproductive isolation when considered in isolation, the study species' spatial distributions and pollinator assemblages overlapped little, such that interspecific pollen transfer is likely uncommon. We did not find evidence that E. albidum and E. mesochoreum differed in mating systems, indicating that self-incompatibility release may not have fostered speciation in this system. Ultimately, we demonstrate that E. albidum and E. mesochoreum are reproductively isolated by multiple, hierarchically-operating barriers, and we add to the currently limited number of studies demonstrating that early acting barriers such as pollinator-mediated isolation can be important for effecting and sustaining reproductive isolation in diploid-polyploid systems.
多倍体在被子植物多样化中发挥了重要作用，但多倍体如何导致生殖隔离仍知之甚少。大多数研究都集中在后合子生殖障碍上，而倍性差异对前合子障碍的影响则研究不足。为了解决这些差距，我们量化了二倍体 Erythronium mesochoreum（百合科）与其四倍体同属 Erythronium albidum 之间杂种出现、种间自交亲和性差异以及多种前合子和后合子障碍对生殖隔离的贡献。研究物种之间的生殖隔离几乎完全，自然发生的杂种很少且大多不育。虽然后合子障碍在单独考虑时对生殖隔离产生了实质性的影响，但研究物种的空间分布和传粉者组合重叠很少，因此种间花粉转移可能不常见。我们没有发现 E. albidum 和 E. mesochoreum 在交配系统上存在差异的证据，表明自交不亲和性的释放可能没有促进该系统的物种形成。最终，我们证明了 E. albidum 和 E. mesochoreum 是通过多个层次作用的障碍进行生殖隔离的，并且我们增加了目前数量有限的研究，证明了早期作用的障碍，如传粉者介导的隔离，对于在二倍体-多倍体系统中产生和维持生殖隔离是重要的。
