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Single or multiple trajectories for the spread of maize cultivation into South America?

玉米种植向南美洲传播的单一或多重轨迹？

基本信息

批准号：
NE/F003250/1
负责人：
Terence Brown
金额：
$ 43.34万
依托单位：
University of Manchester
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2008
资助国家：
英国
起止时间：
2008 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FF003250%2F1
关键词：
Single multiple trajectories spread maize

项目摘要

Maize is the cultivated form of a grass called teosinte, which grows wild in parts of southern and western Mexico. The prehistoric Americans first cultivated maize about 9000 years ago, probably close to the Rio Balsas river in western Mexico. By the time that Europeans arrived in the 15th century AD, maize was being grown throughout the Americas, and was the staple crop for many indigenous civilisations such as the Maya and the Inca. How did maize spread from its centre of origin in Mexico throughout North and South America? The first model for the spread of maize into South America arose from a large study of chromosome structures in different varieties from all over the continent, carried out in the 1970s. Subtle variations in chromosome structure, in particular the positions of small knobs, enabled the genetic relationships between the varieties to be deduced. The pattern of spread was then inferred by comparing these genetics relationships with the geographic location of each variety. The resulting model suggested that maize was initially introduced into the central Andes and from this location spread extensively throughout the highland and lowland regions of the continent, not being significantly supplemented by other types of maize until new varieties spread southwards along the east coast of Brazil in relatively recent times. This model was held to be generally correct until 2002 when it was replaced by the results of a more detailed study of variable DNA sequences called microsatellites, again in different varieties of maize grown throughout South America. This new model holds that the southwards movement of maize from Mexico led first into the lowlands of South America, and only then into the Andes Mountains. Unfortunately, there is a problem with both these models. The geographical distribution of the varieties being studied is a critical component of the analysis, as this distribution, when compared with the genetic relationships between different plants, is what reveals the pattern of spread. This means that in order for the analysis to work, the present-day distribution of the maize varieties must be similar to the pattern set up when maize first spread into South America. But this is unlikely to be the case, because Europeans have had a major impact on South American agriculture, and in particular have been responsible for the extensive movement of maize varieties from one place to another. This movement has created 'noise', obscuring the prehistoric geographic signal and disguising the original pattern of spread. We therefore need to strip off the modern noise to get closer to the prehistoric geographic signal. In a previous project we started to do this by examining archaeological maize specimens that predate the arrival of Europeans, as well as indigenous crops collected from remote native villages which until recently were unaffected by European influences. Our genetic analysis of these archaeological and indigenous specimens suggested that both previous models might be incorrect, and that instead there were two independent routes for the spread of maize cultivation into South America, one along the Andes on the western side of South America, and the second along the lowlands of the northeast coast. Our project was very limited in scope, involving examination of a single short DNA sequence in just eleven indigenous varieties and ten archaeological specimens, most of these from Brazil, and so we cannot yet be sure if our model is accurate. The purpose of the proposed project is to test our model by obtaining substantially more genetic data from a greater number of archaeological specimens and indigenous varieties, from a much broader geographical range throughout South America.

玉米是一种名为类蜀黍的草的栽培形式，这种草在墨西哥南部和西部的部分地区野生生长。大约9000年前，史前美国人首次种植玉米，地点可能靠近墨西哥西部的里奥巴尔萨斯河。当欧洲人于公元 15 世纪抵达时，玉米已在整个美洲种植，并且是玛雅和印加等许多土著文明的主要作物。玉米是如何从墨西哥的起源中心传播到北美和南美的？玉米传播到南美洲的第一个模型源于 20 世纪 70 年代对整个非洲大陆不同品种的染色体结构进行的大规模研究。染色体结构的微妙变化，特别是小瘤的位置，使得能够推断出品种之间的遗传关系。然后通过将这些遗传关系与每个品种的地理位置进行比较来推断传播模式。由此产生的模型表明，玉米最初被引入安第斯山脉中部，并从这个位置广泛传播到整个大陆的高地和低地地区，直到新品种在相对较近的时期沿着巴西东海岸向南传播之前，并没有得到其他类型玉米的显着补充。这个模型一直被认为是正确的，直到 2002 年，它被称为微卫星的可变 DNA 序列更详细的研究结果所取代，同样是在南美各地种植的不同玉米品种中进行的。这个新模型认为，玉米从墨西哥向南移动首先进入南美洲低地，然后才进入安第斯山脉。不幸的是，这两种模型都存在问题。所研究品种的地理分布是分析的关键组成部分，因为与不同植物之间的遗传关系相比，这种分布可以揭示传播模式。这意味着，为了使分析发挥作用，目前玉米品种的分布必须与玉米首次传播到南美洲时建立的模式相似。但事实不太可能是这样，因为欧洲人对南美农业产生了重大影响，特别是对玉米品种从一地到另一地的广泛转移负有责任。这种运动产生了“噪音”，掩盖了史前地理信号并掩盖了原始的传播模式。因此，我们需要去除现代噪音，以更接近史前地理信号。在之前的一个项目中，我们开始通过检查欧洲人到来之前的考古玉米标本，以及从偏远村庄收集的本土作物来做到这一点，这些村庄直到最近才受到欧洲影响。我们对这些考古和土著标本的基因分析表明，之前的两种模型可能都是错误的，相反，玉米种植传播到南美洲有两条独立的路线，一条沿着南美洲西侧的安第斯山脉，第二条沿着东北海岸的低地。我们的项目范围非常有限，只涉及检查 11 个本土品种和 10 个考古标本（其中大部分来自巴西）的单个短 DNA 序列，因此我们尚不能确定我们的模型是否准确。拟议项目的目的是通过从整个南美洲更广泛的地理范围内的更多考古标本和本土品种获得更多的遗传数据来测试我们的模型。