Genetic Consequences of Pre-Columbian Agave Cultivation in Central Arizona

尽管龙舌兰在中美洲的民族植物学重要性早已得到承认，但在目前分隔美国和墨西哥的国际边界以北的土著民族种植龙舌兰的记录直到20世纪80年代才有记录。从那时起，几位学者对前哥伦布文化在索诺兰沙漠北部种植龙舌兰进行了研究，但仍有许多问题。这项研究项目将研究哥伦布前的种植对三种龙舌兰的遗传影响，这三种龙舌兰是在公元600年至1350年期间由亚利桑那州中部的几种史前文化种植的。由于其中两个种(龙舌兰和龙舌兰)仅在考古遗址中被发现，它们被认为是栽培植物或农作物。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一个谜。第三种(A.parryi)既存在于野生种群中，也存在于栽培种群中，后者中的一些物种构成了据称是由人类引起的范围扩大的区域。由于它们的寿命和营养繁殖，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哥伦布之前的驯化过程，以及史前栽培对野生植物遗传变异性和结构的影响。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)确定这两个栽培种内的遗传变异水平，(2)弄清它们从墨西哥独立引入亚利桑那州中部的次数，(3)鉴定栽培种的祖先，(4)确定不同文化背景下对不同性状的人类选择是否不同，(5)比较野生和栽培种群内遗传多样性的水平和划分，以及(6)确定该物种的栽培种群是否都来自同一创始人。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。这个项目将在一个几乎未被探索的作物进化领域开辟新的天地。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。分子标记已被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)属之间的分类关系。它们在这项研究中的使用将澄清该科Ditepalae组之间鲜为人知的分类关系，并将评估哥伦布前的耕作对这两个栽培种和A.parryi的遗传后果。在亚利桑那州的一小块土地上生长着两种非常稀有的植物--黑曲霉和黑曲霉。根据濒危物种法案、古物法案和历史保护法案，这两个物种都得到了保护，但许多物种已经通过城市发展和水库蓄水而被摧毁。该项目将促进对这些重要的史前培植者及其培育的文化背景的基本了解，并将协助确保保护他们的努力。

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.