Genetic Consequences of Pre-Columbian Agave Cultivation in Central Arizona

虽然龙舌兰在中美洲民族植物学上的重要性早已被认识到，但直到20世纪80年代，在美国和墨西哥目前的国际边界以北的土著居民种植龙舌兰才被记录下来。从那时起，几位学者研究了索诺兰沙漠北部前哥伦布文明的龙舌兰种植，但仍存在许多问题。这个研究项目将检查前哥伦布时期的种植对三种龙舌兰的遗传影响，这三种龙舌兰是由亚利桑那州中部的几个史前文化从公元600年到1350年种植的。由于其中两种龙舌兰（Agave murpheyi和A. delamateri）仅在考古遗址中被发现，因此它们被认为是栽培植物或作物植物。它们很可能是沿着史前贸易路线从墨西哥向北运输的，尽管它们的祖先物种的身份仍然是个谜。第三种（A. parryi）既存在于野生种群中，也存在于栽培种群中，后者中的一些构成了一个据称由人类引起的范围扩张的区域。由于它们的长寿和营养繁殖，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哥伦布发现新大陆前的驯化过程，以及史前种植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分析的结合）来检查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)确定两种菌株的遗传变异水平，(2)阐明它们从墨西哥独立引入亚利桑那州中部的次数，(3)确定两种菌株的祖先，(4)确定人类对A. murpheyi不同性状的选择是否因文化背景而异，(5)比较A. parryi野生种群和栽培种群的遗传多样性水平和分配。(6)确定该种的栽培居群是否均来自同一始祖。用于分子分析的叶子样本将从三个目标物种及其在亚利桑那州和墨西哥的近亲中收集。这个项目将在一个几乎未开发的作物进化领域开辟新天地。因为大多数研究都集中在作为商业或传统农业系统一部分的现代作物上；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）家族内属间的分类关系。它们在本研究中的使用将澄清该科双叶属类群中尚不清楚的分类关系，并将评估前哥伦布时期栽培对这两个品种和parryi的遗传影响。a. murpheyi和a. delamateri都是非常罕见的植物，分布在亚利桑那州的一小块地区。根据《濒危物种法》、《古物法》和《历史保护法》，这两个物种都得到了保护，但由于城市发展和水库蓄水，许多物种已经灭绝。该项目将促进对这些重要史前文化的基本认识，以及它们被种植的文化背景，并将有助于确保它们的保存。

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.