Arnesen Spencer, Coleman Craig E, Meyer Susan E
Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah 84602 USA.
USFS Rocky Mountain Research Station, Shrub Sciences Laboratory, 735 North 500 East, Provo, Utah 84606 USA
Am J Bot. 2017 Jun;104(6):879-890. doi: 10.3732/ajb.1700038. Epub 2017 Jun 20.
Invasive species are often initially restricted to a narrow range and may then expand through any of multiple mechanisms including phenotypic plasticity, in situ evolution, or selection on traits preadapted for new habitats. Our study used population genetics to explore possible processes by which the highly selfing invasive annual grass has expanded into montane environments.
We used 69 single nucleotide polymorphic (SNP) markers to genotype ca. 20 individuals from each of 38 montane cheatgrass populations from throughout the Intermountain West and to identify characteristic SNP haplotypes and examine their distribution.
Five invariant SNP haplotypes were dominant in montane cheatgrass populations, making up 59% of genotyped individuals, with each haplotype present in 12 to 21 populations. Four of these were absent or present at low frequency in low elevation populations, while the fifth was also sometimes dominant at low elevation. Sixteen haplotypes made up 78% of all genotyped individuals. These haplotypes were distributed across several haplogroups within the clade that also includes most sagebrush steppe lineages.
The wide geographic distribution of several common haplotypes almost completely restricted to montane habitats suggests that dominant lineages in montane populations may possess adaptive syndromes that are preserved through reduced outcrossing rates or negative selection on outcrossed progeny. However, conclusive evidence of such local adaptation requires reciprocal seeding experiments and further characterization of adaptive traits and breeding system characteristics. Other lineages have likely risen to dominance in montane populations through selectively neutral processes.
入侵物种最初通常局限于狭窄的范围，随后可能通过多种机制中的任何一种进行扩张，包括表型可塑性、原地进化或对适应新栖息地的性状进行选择。我们的研究利用群体遗传学来探索高度自交的入侵一年生草本植物扩散到山地环境的可能过程。
我们使用69个单核苷酸多态性（SNP）标记对来自美国西部山间地区38个山地黑麦草种群中约20个个体进行基因分型，以识别特征性SNP单倍型并检查它们的分布。
5种不变的SNP单倍型在山地黑麦草种群中占主导地位，占基因分型个体的59%，每个单倍型存在于12至21个种群中。其中4种在低海拔种群中不存在或频率较低，而第5种在低海拔地区有时也占主导地位。16种单倍型占所有基因分型个体的78%。这些单倍型分布在该进化枝内的几个单倍群中，该进化枝还包括大多数蒿属草原谱系。
几种几乎完全局限于山地栖息地的常见单倍型的广泛地理分布表明，山地种群中的优势谱系可能具有通过降低异交率或对异交后代进行负选择而得以保留的适应综合征。然而，这种局部适应的确凿证据需要进行相互播种实验以及对适应性状和繁殖系统特征进行进一步表征。其他谱系可能通过选择性中性过程在山地种群中占据主导地位。
