Genetic Consequences of Pre-Columbian Agave Cultivation in Central Arizona

University Of Georgia Research Foundation Inc, Athens GA

Investigators

Abstract

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.