School of Biological Sciences, Washington State University, Pullman, WA, 99164, USA.
Department of Biological Sciences, Boise State University, 1910 University Dr., Boise, ID, 83725-1515, USA.
Heredity (Edinb). 2021 Jan;126(1):178-193. doi: 10.1038/s41437-020-00354-0. Epub 2020 Aug 19.
Genetic diversity within and among 42 native populations of Bromus tectorum (cheatgrass) was characterized within two regions, the eastern Mediterranean and the western Mediterranean. Two hypotheses were tested for the genetic diversity of these populations: (1) populations from the eastern Mediterranean are more genetically diverse compared with populations to the west, a potential consequence of the species' westward dispersal with the spread of agriculture, and (2) populations across the Mediterranean contain comparable genetic diversity but display high genetic differentiation, a potential consequence of both regions having served as refugia during glacial advances in the late Quaternary Period. Populations in the eastern Mediterranean possess 16 polymorphic loci and 37 multilocus genotypes. In contrast, populations from the western Mediterranean include a subset of these polymorphic loci (9) and fewer multilocus genotypes (19), consistent with the dispersal of B. tectorum with the east-west Holocene spread of agriculture. Among the 19 multilocus genotypes identified in populations from the western Mediterranean, 13 are undetected among eastern Mediterranean populations. Average genetic diversity within populations from the eastern Mediterranean is nonetheless comparable to the genetic diversity in populations from the Iberian Peninsula, whereas diversity is the lowest in the populations from southern France. Our results suggest a prominent role for agriculture in the grass's western spread, although glacial history and environmental heterogeneity also could have influenced the grass's genetic diversity. The exceptionally high level of self-pollination (>99%) in B. tectorum has contributed to preserving the genetic signature associated with the species' biogeographical history across the Mediterranean region.
对分布于东地中海和西地中海两个地区的 42 个野生狗尾草（也就是莠草）本地种群进行了遗传多样性分析。对这些种群的遗传多样性提出了两个假设：（1）与西部种群相比，东部地中海种群的遗传多样性更为丰富，这可能是由于该物种随着农业的传播而向西扩散的结果；（2）地中海地区的种群具有相似的遗传多样性，但表现出较高的遗传分化，这可能是因为两个地区都曾在第四纪晚期的冰川扩张中充当避难所。东部地中海地区的种群拥有 16 个多态性位点和 37 个多位点基因型。相比之下，来自西地中海地区的种群包含这些多态性位点中的一个子集（9 个）和较少的多位点基因型（19 个），这与莠草随农业在东西方向的全新世传播而扩散的情况一致。在西地中海地区种群中发现的 19 个多位点基因型中，有 13 个在东地中海地区的种群中未被发现。尽管如此，东地中海地区种群的平均遗传多样性仍与伊比利亚半岛种群的遗传多样性相当，而法国南部种群的多样性最低。研究结果表明，农业在该草种的西向扩散中起着重要作用，尽管冰川历史和环境异质性也可能影响该草种的遗传多样性。狗尾草极高的自交率（>99%）有助于保存与该物种在整个地中海地区的生物地理历史相关的遗传特征。
