Abstract
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 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 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.
Highlights
The genetics and phenotypic diversity of Zea mays Lam. has been one of the main topics of study in the attempt to understand the domestication process and the evolutionary history of crops [1,2]
The changes observed in Tarapacamaize
In the hyperarid conditions of the Atacama Desert, no crops can survive without human assistance
Summary
The genetics and phenotypic diversity of Zea mays Lam. (maize) has been one of the main topics of study in the attempt to understand the domestication process and the evolutionary history of crops [1,2]. Archaeologist describe domestication as the transformation of wild species into a domestic descendant [5] The latter would present characteristics such as reproductive isolation, the human dependence of the plant for its survival or variations of its grain size, shape, physiological and genetics that differentiate it from its predecessor [6]. A more comprehensive and flexible idea of domestication considers this process as a continuum of changes in plants species caused by the interaction between human groups and their environments. Changes such as increased/decreased in size’s seed and fruits are not always instantaneous or final stages of people-plants interaction [6,7]. The archaeobotanical record exhibits many intermediate stages of plants remains
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