Palmer Sarah A, Moore Jonathan D, Clapham Alan J, Rose Pamela, Allaby Robin G
Warwick HRI, The University of Warwick, Wellesbourne, UK.
PLoS One. 2009 Jul 22;4(7):e6301. doi: 10.1371/journal.pone.0006301.
Archaeobotanical samples of barley (Hordeum vulgare L.) found at Qasr Ibrim display a two-row phenotype that is unique to the region of archaeological sites upriver of the first cataract of the Nile, characterised by the development of distinctive lateral bracts. The phenotype occurs throughout all strata at Qasr Ibrim, which range in age from 3000 to a few hundred years.
We extracted ancient DNA from barley samples from the entire range of occupancy of the site, and studied the Vrs1 gene responsible for row number in extant barley. Surprisingly, we found a discord between the genotype and phenotype in all samples; all the barley had a genotype consistent with the six-row condition. These results indicate a six-row ancestry for the Qasr Ibrim barley, followed by a reassertion of the two-row condition. Modelling demonstrates that this sequence of evolutionary events requires a strong selection pressure.
The two-row phenotype at Qasr Ibrim is caused by a different mechanism to that in extant barley. The strength of selection required for this mechanism to prevail indicates that the barley became locally adapted in the region in response to a local selection pressure. The consistency of the genotype/phenotype discord over time supports a scenario of adoption of this barley type by successive cultures, rather than the importation of new barley varieties associated with individual cultures.
在卡斯尔伊布里姆发现的大麦（Hordeum vulgare L.）考古植物样本呈现出两行型表型，这在尼罗河第一瀑布上游考古遗址所在区域是独一无二的，其特征是独特的侧苞片发育。这种表型出现在卡斯尔伊布里姆的所有地层中，其年代范围从3000年到几百年不等。
我们从该遗址整个居住范围内的大麦样本中提取了古代DNA，并研究了现存大麦中负责行数的Vrs1基因。令人惊讶的是，我们在所有样本中都发现了基因型与表型之间的不一致；所有大麦的基因型都与六行型情况一致。这些结果表明卡斯尔伊布里姆大麦的祖先是六行型，随后又恢复为两行型。模型表明，这种进化事件序列需要强大的选择压力。
卡斯尔伊布里姆的两行型表型是由与现存大麦不同的机制导致的。这种机制占主导地位所需的选择强度表明，大麦是为了应对当地的选择压力而在该地区实现了本地适应性。随着时间推移，基因型/表型不一致的一致性支持了一种观点，即这种大麦类型被连续的文化所采用，而不是与个别文化相关的新大麦品种的引进。
