Genetic and phenotypic diversity in 2000 years old maize (Zea mays L.) samples from the Tarapacá region, Atacama Desert, Chile (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
We report the first genetic analysis of archeological maize specimens from the site of San Lorenzo (1,500-700 BP) (Azapa valley, Arica, Chile). Ancient DNA was successfully isolated from 11 archeological maize grains. The Alcohol dehydrogenase 2 (Adh2) gene was analyzed because it has a highly variable region due to the presence of a microsatellite region around -28 to -8, which consists of GA repeats that may be present in three types GAn, GAnTA and GA1AA1GAn, which is used as an informative region of the routes of initial dispersion of maize. Five Adh2 alleles were obtained and the alignment of these sequences according to the variable region revealed the presence of the three types of GA repeated. Our results do not provide sufficient evidence to reject any maize spread model proposed. This is the first report focused on genetic analysis of maize associated with an archeological site in Chile.
Journal of Archaeological Science, 2003
To study the origins of South American maize, without the complicating factors introduced by the extensive movement of genotypes during the post-Columbian period, we made a genetic analysis of primitive landraces and preserved maize remains. Fifteen alcohol dehydrogenase 2 (Adh2) allele sequences were obtained from the landraces and 11 from the archaeological specimens. When these and six previously published Adh2 sequences were aligned, three allele groups were seen, distinguished by the structure of a dinucleotide repeat sequence. The three allele groups had distinct distributions within South America, the distributions supporting a model in which the two Central American agricultural systems-highland and lowland-generated separate expansions of maize cultivation into South America. One expansion centred on a highland culture that spread from Central America through the Panama highlands into the Andean regions on the western side of South America, and the second expansion centred on a lowland culture which spread along the lowlands of the northeast coast of South America, entering the continent through the river systems. The Adh2 biogeography was consistent with limited cultural contact across the Andes between northern Chile and Paraguay. From the diversity of the Adh2 allele sequences, we deduced that maize has undergone a rapid rate of evolution since domestication.
Domestication and evolution of maize
International Journal of Chemical Studies
Around ten thousand years ago, men mostly relied on hunting and gathering activities before shifting to agriculture and allied practices. By 4000 years ago, ancient people had completed the domestication of all major crop species upon which human survival is dependent, including rice, wheat, and maize. Recent advances have started to point out the genes that were responsible for this change of the cultivated maize crop. The list of genes to date tentatively suggests that diverse plant developmental pathways were the targets of Neolithic "genetic tinkering," Maize and its closest wild relatives, the teosintes, present a paradox. Even though maize and the teosintes exhibit extreme differences in their adult morphologies their genomes are so similar that they share the same chromosome number, similar or identical chromosome morphologies, and they can be easily cross-hybridized. A very high level of diversity exists among the maize landraces to explain this diversity many workers have proposed that maize landraces were the products of multiple independent domestication from their wild relative. Reports indicate that all maize arose from a single domestication in southern Mexico about 9,000 years ago. This phylogenetic work is consistent with a model based on the archaeological record suggesting that maize was the result of early Holocene domesticates. A few major genes or multiple linked minor genes on the maize chromosome largely govern the drastic change that is seen between teosinte and maize. Genes like teosinte branched1 (tb1) gene, teosinte glume architecture1 (tga1) and Zea Floricaula / Leafy2 (zfl2). There still remain some untold chapters in the origin and early diversification of maize. These questions will require additional archaeological and botanical exploration, more powerful molecular analyses, and perhaps DNA analysis of archaeological materials such that a perfect phylogenetic relationship can be established.
Proceeding of the Royal Academy of London 274(1609): 545-554. , 2007
Archaeological maize specimens from Andean sites of southern South America, dating from 400 to 1400 years before present, were tested for the presence of ancient DNA and three microsatellite loci were typed in the specimens that gave positive results. Genotypes were also obtained for 146 individuals corresponding to modern landraces currently cultivated in the same areas and for 21 plants from Argentinian lowland races. Sequence analysis of cloned ancient DNA products revealed a high incidence of substitutions appearing in only one clone, with transitions prevalent. In the archaeological specimens, there was no evidence of polymorphism at any one of the three microsatellite loci: each exhibited a single allelic variant, identical to the most frequent allele found in contemporary populations belonging to races Amarillo Chico, Amarillo Grande, Blanco and Altiplano. Affiliation between ancient specimens and a set of races from the Andean complex was further supported by assignment tests. The striking genetic uniformity displayed by the ancient specimens and their close relationship with the Andean complex suggest that the latter gene pool has predominated in the western regions of southern South America for at least the past 1400 years. The results support hypotheses suggesting that maize cultivation initially spread into South America via a highland route, rather than through the lowlands. Microsatellite typing of ancient maize V. V. Lia et al. 547 Proc. R. Soc. B (2007) Microsatellite typing of ancient maize V. V. Lia et al. 553
PLoS ONE, 2012
Background: The species Zea mays includes both domesticated maize (ssp. mays) and its closest wild relatives known as the teosintes. While genetic and archaeological studies have provided a well-established history of Z. mays evolution, there is currently minimal description of its current and past distribution. Here, we implemented species distribution modeling using paleoclimatic models of the last interglacial (LI; ,135,000 BP) and the last glacial maximum (LGM; ,21,000 BP) to hindcast the distribution of Zea mays subspecies over time and to revisit current knowledge of its phylogeography and evolutionary history.
The Antiquity, Biogeography and Culture History of Maize in Mesoamerica.
Histories of Maize in Mesoamerica: Multidisciplinary Approaches., 2010
Domestication genetic change in population due to interaction with humans that leads to a dependence relation. Agriculture the mutual dependence of crop plant and humans Anagenesis the persistence of one or a suite of biological traits that over time leads to varietal divergence Cladogenesis the development of evolutionary novelty through the extinction of preexisting forms Dietary reliance subsistent dependence on a specific crop or trophic level.