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.

中文翻译：

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地中海地区雀麦（禾本科）的遗传分析：本地种群的生物地理格局

在东地中海和西地中海这两个地区内和之间的 42 个本地雀麦 (cheatgrass) 种群内和之间的遗传多样性被表征。对这些种群的遗传多样性进行了两个假设：(1) 地中海东部的种群与西部的种群相比在遗传上更具多样性，这是该物种随着农业的传播向西扩散的潜在结果，以及 (2)整个地中海的种群具有相当的遗传多样性，但显示出高度的遗传分化，这是两个地区在第四纪晚期冰川进展期间作为避难所的潜在结果。地中海东部的种群拥有 16 个多态位点和 37 个多位点基因型。相比之下，地中海西部的种群包括这些多态基因座的一个子集（9）和较少的多位点基因型（19），这与 B. tectorum 的传播与全新世东西方农业的传播一致。在西地中海人群中鉴定的 19 种多位点基因型中，有 13 种在东地中海人群中未被发现。尽管如此，地中海东部人群的平均遗传多样性与伊比利亚半岛人群的遗传多样性相当，而法国南部人群的多样性最低。我们的研究结果表明，农业在草的西部传播中发挥了重要作用，尽管冰川历史和环境异质性也可能影响草的遗传多样性。