Inferences from the Historical Distribution of Wild and Domesticated Maize Provide Ecological and Evolutionary Insight (original) (raw)
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Genetic and phenotypic diversity in 2000 years old maize (Zea mays L.) samples from the Tarapaca´ region, Atacama Desert, Chile, 2019
The evolution of maize (Zea mays L.) is highly controversial given the discrepancies related to the phenotypic and genetic changes suffered by the species, the incidence of human groups and the times in which these changes occurred. Also, morphological and genetic traits of crops are difficult to evaluate in the absence of fossils macro-botanical remains. In contrast in the Tarapaca´ region (18–21˚ S), Atacama Desert of Chile, prehispanic settlements (ca. 2500–400 yr BP) displayed extensive maize agriculture. The presence of archaeological macro-botanical remains of maize provided a unique opportunity to study the evolution of this crop, covering a temporal sequence of at least 2000 years. Thus, in this study, we ask how the morphological and genetic diversity of maize has varied since its introduction during prehispanic times in the Tarapaca´ region. To answer this, we measured and compared morphological traits of size and shape between archaeological cobs and kernels and 95 ears from landraces. To established genetic diversity eight microsatellite markers (SSR) were analyzed in archaeological and modern kernels. Genetic diversity was estimated by allelic frequency rates, the average number of alleles per locus, observed heterozygosity (Ho) and expected heterozygosity (He). Differences between populations and genetic structure were estimated by fixation index FST and STRUCTURE analysis. Our results indicate significant phenotypic differences and genetic distance between archaeological maize and landraces. This result is suggestive of an introduction of new varieties or drastic selective changes in modern times in Tarapaca´ . Additionally, archaeological maize shows a low genetic diversity and a progressive increase in the size of ears and kernels. These results suggest a human selection during prehispanic times and establish that prehispanic farmers played an important role in maize development. They also provide new clues for understanding the evolutionary history of maize in hyperarid conditions
PLOS ONE, 2019
The evolution of maize (Zea mays L.) is highly controversial given the discrepancies related to the phenotypic and genetic changes suffered by the species, the incidence of human groups and the times in which these changes occurred. Also, morphological and genetic traits of crops are difficult to evaluate in the absence of fossils macro-botanical remains. In contrast in the Tarapacá region (18-21˚S), Atacama Desert of Chile, prehispanic settlements (ca. 2500-400 yr BP) displayed extensive maize agriculture. The presence of archaeological macro-botanical remains of maize provided a unique opportunity to study the evolution of this crop, covering a temporal sequence of at least 2000 years. Thus, in this study, we ask how the morphological and genetic diversity of maize has varied since its introduction during prehispanic times in the Tarapacá region. To answer this, we measured and compared morphological traits of size and shape between archaeological cobs and kernels and 95 ears from landraces. To established genetic diversity eight microsatellite markers (SSR) were analyzed in archaeological and modern kernels. Genetic diversity was estimated by allelic frequency rates, the average number of alleles per locus, observed heterozygosity (Ho) and expected heterozygosity (He). Differences between populations and genetic structure were estimated by fixation index F ST and STRUCTURE analysis. Our results indicate significant phenotypic differences and genetic distance between archaeological maize and landraces. This result is suggestive of an introduction of new varieties or drastic selective changes in modern times in Tarapacá. Additionally, archaeological maize shows a low genetic diversity and a progressive increase in the size of ears and kernels. These results suggest a human selection during prehispanic times and establish that prehispanic farmers played an important role in maize development. They also provide new clues for understanding the evolutionary history of maize in hyperarid conditions.
Proceedings of the National Academy of Sciences
Mexico is recognized as the center of origin and domestication of maize. Introduction of modern maize varieties (MVs) into Mexico raised concerns regarding the possible effects of gene flow from MVs into maize landraces (LRs) and their wild relatives (WRs), teosintes. However, after more than 60 y from the release of the first MVs, the impact of the sympatry with LRs and their WRs has not been explored with genetic data. In this work, we assessed changes in the genomes of 7 maize LRs and 2 WR subspecies from collections spanning over 70 y. We compared the genotypes obtained by genotyping by sequencing (GBS) for LRs and WRs before and after the adoption of MVs, and observed introgression from sympatric MVs into LRs and into the WR Zea mays ssp. mexicana sampled after the year 2000. We also found a decrease in the paired divergence index (FST) between MV-LR and MV-WR over the same time frame. Moreover, we determined that LR genetic diversity increased after 2000, probably as a result ...
Genetic Resources and Crop Evolution, 2007
The classification of Mexican maize (Zea mays L.) begun since the early 20th century, it was consolidated during the middle of this century, but recent additions and rearrangements have been performed by several authors employing new methods of analysis and collections from diverse origin; nevertheless, maize from the State of Michoacan, Mexico has received little attention in regard to its systematic classification. Maize populations from the Tarasca Mountain Chain in Michoacan are commonly considered in literature, as belonging to the Chalquen˜o race; however, closer observations indicate that significant differences do exist, suggesting the necessity of performing an in-depth study on this respect. Thirty nine native maize populations from the Tarasca Mountain Chain region were evaluated along with 19 typical populations of the Chalquen˜o, Celaya and Conico races coming from the States of Mexico, Puebla, Hidalgo, Quere´taro and Oaxaca. Populations were evaluated in Aranza, Michoacan and Montecillo, Mexico State. Seventeen morphological characters were scored and analyzed by one-way analyses of variance and multivariate techniques. Populations were also genetically analyzed through 17 isozyme loci. Native populations had some alleles not found either in the Chalquen˜o, Celaya or Conico races, and possess larger genetic diversity. Local populations were congregated into a discrete group apart from the typical Chalquen˜o populations, suggesting that landraces from the Tarasca Mountain Chain region might not be considered as belonging to the Chalquen˜o race, but they integrate by themselves a different race.
The paleobiolinguistics of maize (Zea mays L.)
Ethnobiology Letters, 5: 52‐64. DOI: 10.14237/ebl.5.2014.130, 2014
Paleobiolinguistics is used to determine when and where maize (Zea mays L.) developed significance for different prehistoric groups of Native America. Dates and locations of proto‐languages for which maize terms reconstruct generally accord with crop‐origin and dispersal information from plant genetics and archaeobotany. Paleobiolinguistic and other lines of evidence indicate that human interest in maize was extensive millennia before the widespread development of a village farming way of life in the New World,
A 2,000-year reconstruction of the rain-fed maize agricultural niche in the US Southwest
Nature communications, 2014
Humans experience, adapt to and influence climate at local scales. Paleoclimate research, however, tends to focus on continental, hemispheric or global scales, making it difficult for archaeologists and paleoecologists to study local effects. Here we introduce a method for high-frequency, local climate-field reconstruction from tree-rings. We reconstruct the rain-fed maize agricultural niche in two regions of the southwestern United States with dense populations of prehispanic farmers. Niche size and stability are highly variable within and between the regions. Prehispanic rain-fed maize farmers tended to live in agricultural refugia--areas most reliably in the niche. The timing and trajectory of the famous thirteenth century Pueblo migration can be understood in terms of relative niche size and stability. Local reconstructions like these illuminate the spectrum of strategies past humans used to adapt to climate change by recasting climate into the distributions of resources on whic...
Context and Background on Maize and its Wild Relatives in Mexico
Maize is the predominant crop of the world. About 30 percent of world production is used for direct human consumption and as an industrial input, while 70 percent is used as animal feed. Mexico safeguards the main genetic diversity of maize and its wild relative teosinte, both plants native to the country. The oldest known maize ear relics were excavated in a cave in the Mexican state of Oaxaca, and were dated 6250 years before the present era. Native Mesoamericans domesticated maize, invented nixtamalization, and developed maize from a 6 cm long, popping-kernel ear to what we now recognize as modern maize with its wide variety in ear size, kernel texture, color, size, and adequacy for diverse uses. In fact, native Mesoamericans continue to develop maize on more than one million small farms in Mexico. These farmers grow their own seed and depend on maize as their main source of food. In doing this, some 84 Mexican ethnic groups are also acting as stewards of maize genetic diversity. Transgenic food-maize has been detected—albeit in variable proportions—deep in the heartland of Mexican traditional agriculture. The Mexican Federal Government adopted a de facto moratorium to commercial production of transformed maize through its Ministry of Agriculture in 1998, but has allowed maize imports that may include transgenic maize. Expected consequences of the presence of transformed maize in Mexico are analyzed in this book. Those consequences involve a number of issues: status of genetic diversity of maize and its wild relatives, natural ecosystems, agriculture, human and animal health, society and culture, risks and opportunities. In this chapter, we will look at maize and its wild relatives in Mexico, from the time of maize domestication to the present. We will also examine some elements of the traditional approach to developing maize as a crop and conserving its genetic diversity, as well as its present day distribution in Mexico, and dispersion throughout the world. Finally, we will look into transformed maize and how it could interact with maize landraces.