Genetic Consequences of Pre-Columbian Agave Cultivation in Central Arizona

虽然龙舌兰在中美洲的民族植物学重要性早已得到承认，但直到20世纪80年代，美国和墨西哥之间的国际边界以北的土著人民才有记录。 从那时起，几位学者研究了北方索诺兰沙漠前哥伦布文化中的龙舌兰种植，但仍存在许多问题。 该研究项目将研究前哥伦布时期种植对三种龙舌兰品种的遗传影响，这些龙舌兰品种是由亚利桑那州中部的几种史前文化从公元600年到1350年种植的。 因为其中两种龙舌兰（Agave murpheyi和A. delamateri）仅在考古遗址中发现，它们被认为是栽培植物或作物。 它们很可能是沿着沿着史前贸易路线从墨西哥向北运输的，尽管它们祖先物种的身份仍然是个谜。 第三种是A。parryi）存在于野生和栽培种群中，其中一些种群构成了据称是人类引起的分布范围扩大的区域。 由于它们的长寿和营养繁殖，再加上大约1450年后该地区没有龙舌兰种植，这三种龙舌兰提供了一个独特的机会来研究前哥伦布驯化过程，以及史前栽培实践对野生植物遗传变异和结构的影响。 研究人员将使用分子技术（等位酶，微卫星，叶绿体DNA和核糖体DNA分析的组合）来研究该地区龙舌兰种植的文化和进化方面。 该项目的具体目标是（1）确定两个栽培种内的遗传变异水平，（2）澄清它们从墨西哥独立引入亚利桑那州中部的次数，（3）确定栽培种的祖先，（4）确定人类是否选择A. murpheyi的遗传多样性随文化背景的不同而不同。（5）比较了野生和栽培群体的遗传多样性水平和分配。parryi，和（6），以确定是否本种的栽培种群都来自同一创始人。 用于这些分子分析的叶片样本将从亚利桑那州和墨西哥的三个目标物种及其近亲的种群中收集。该项目将在作物进化的一个几乎未探索的领域开辟新天地。 因为大多数研究都集中在商业或传统农业系统中的现代作物上;对史前植物驯化的了解要少得多。 分子标记已成功地用于研究其他作物的驯化过程，并确定龙舌兰科（龙舌兰）属间的分类关系。 在这项研究中，它们的使用将澄清该科的Ditepalae组内鲜为人知的分类学关系，并将评估前哥伦布时期种植对这两个栽培种和A. parryi。 A. murpheyi和A.德拉马特里是非常罕见的植物，分布在亚利桑那州的一小块地区。 根据《濒危物种法》、《文物法》和《历史保护法》，这两个物种都受到了保护，但许多种群已经被城市发展和水库蓄水所摧毁。 该项目将促进对这些重要的史前栽培物及其栽培文化背景的基本了解，并将协助确保其保护的努力。

Although its ethnobotanical importance in Mesoamerica has long been recognized, agave cultivation by indigenous peoples north of the present international boundary separating the U.S. and Mexico was not documented until the 1980s. Since then, agave cultivation by pre-Columbian cultures in the northern Sonoran Desert has been studied by several scholars, but many questions remain. This research project will examine the genetic effects of pre-Columbian cultivation on three agave species that were grown by several prehistoric cultures in central Arizona from about 600 to 1350 A.D.. Because two of these species (Agave murpheyi and A. delamateri) are only found in association with archeological sites, they have been considered to be cultigens, or crop plants. They were most likely transported north from Mexico along prehistoric trade routes, although the identity of their ancestral species remains a mystery. The third species (A. parryi) exists in both wild and cultivated populations, with some of the latter constituting an area of purported human-induced range expansion. Thanks to their longevity and vegetative reproduction, coupled with the absence of agave cultivation in this area after roughly 1450, these three agave species provide a unique opportunity to study the pre-Columbian domestication process, as well as the effects of prehistoric cultivation practices on the genetic variability and structure of wild plants. The investigators will use molecular techniques (a combination of allozyme, microsatellite, chloroplast DNA, and ribosomal DNA analysis) to examine both cultural and evolutionary aspects of agave cultivation in this region. Specific objectives of the project are (1) to determine levels of genetic variability within the two cultigens, (2) to clarify the number of times they were independently introduced into central Arizona from Mexico, (3) to identify the ancestors of the cultigens, (4) to determine whether human selection for different traits in A. murpheyi differed with cultural context, (5) to compare levels and partitioning of genetic diversity within wild and cultivated populations of A. parryi, and (6) to determine whether cultivated populations of this species were all derived from the same founder. Leaf samples for these molecular analyses will be collected from populations of the three target species and their close relatives in Arizona and Mexico.This project will break new ground in a virtually unexplored area of crop evolution. Because most research has focused on modern crops that are part of either a commercial or traditional agricultural system; much less is known about prehistoric plant domestication. Molecular markers have been used successfully to examine the domestication process in other crops, and to determine taxonomic relationships among genera within the Agavaceae (agave) family. Their use in this study will clarify poorly understood taxonomic relationships within the Ditepalae group of that family, and it will assess the genetic consequences of pre-Columbian cultivation on these two cultigens and A. parryi. Both A. murpheyi and A. delamateri are very rare plants that range over a small area of Arizona. Protection has been sought for both species under the Endangered Species Act, the Antiquities Act, and the Historic Preservation Act, but many populations have already been destroyed through urban development and reservoir impoundment. This project will advance fundamental knowledge of these important prehistoric cultigens and the cultural context within which they were cultivated, and it will assist efforts to ensure their preservation.