Abstract
Domestication is a continuous evolutionary process guided by humans. This process leads to divergence in characteristics such as behaviour, morphology or genetics, between wild and managed populations. Agaves have been important resources for Mesoamerican peoples since prehistory. Some species are domesticated and others vary in degree of domestication. Agave inaequidens Koch is used in central Mexico to produce mescal, and a management gradient from gathered wild and silvicultural populations, as well as cultivated plantations, has been documented. Significant morphological differences were reported among wild and managed populations, and a high phenotypic variation in cultivated populations composed of plants from different populations. We evaluated levels of genetic diversity and structure associated with management, hypothesizing that high morphological variation would be accompanied by high genetic diversity in populations with high gene flow and low genetic structure among managed and unmanaged populations. Wild, silvicultural and cultivated populations were studied, collecting tissue of 19-30 plants per population. Through 10 nuclear microsatellite loci, we compared population genetic parameters. We analysed partition of variation associated with management categories to estimate gene flow among populations. Agave inaequidens exhibits high levels of genetic diversity (He = 0.707) and moderate genetic structure (FST = 0.112). No differences were found in levels of genetic diversity among wild (He = 0.704), silviculturally managed (He = 0.733) and cultivated (He = 0.698) populations. Bayesian analysis indicated that five genetic clusters best fit the data, with genetic groups corresponding to habitats where populations grow rather than to management. Migration rates ranged from zero between two populations to markedly high among others (M = 0.73-35.25). Natural mechanisms of gene flow and the dynamic management of agave propagules among populations favour gene flow and the maintenance of high levels of variation within all populations. The slight differentiation associated with management indicates that domestication is in an incipient stage.
Highlights
Domestication is a gradual and continuous process through which plants undergo phenotypic and genetic changes, mainly resulting from artificial selection favouring organisms with features desirable, necessary or interesting to humans (Darwin 1859; Casas et al 2007; Pickersgill 2007)
A global test of linkage equilibrium (LE) indicated that genotypes at one pair of loci (APAR2-12 and APARLC28, Lindsay et al 2012) are not independent (P ≤ 0.05), but identical results were found in the rest of the analysis when either of these loci was removed
No genetic divergence was detected among populations according to management practice, which indicates that management and artificial selection documented to occur on A. inaequidens by other studies (Figueredo et al 2014; Torres et al 2015b) have not affected genetic diversity within the species
Summary
Domestication is a gradual and continuous process through which plants undergo phenotypic and genetic changes, mainly resulting from artificial selection favouring organisms with features desirable, necessary or interesting to humans (Darwin 1859; Casas et al 2007; Pickersgill 2007). Numerous native plant species (.800) are at various stages of domestication in traditional farming systems, such as home gardens and other agroforestry systems, most of them still unstudied (Colunga-GarcıaMarın and Zizumbo-Villarreal 1993; Casas et al 1997, 2007; Caballero et al 1998; Blancas et al 2010). In Mesoamerica, people practice in situ management of wild plants in forests, forest patches and agroecosystems, which includes several types of interaction: letting stand, encouraging growth and special care and protection of more favourable plants These interactions in some cases involve artificial selection, resulting in documentable domestication processes (Colunga-GarcıaMarın and Zizumbo-Villarreal 1993; Casas et al 1996, 2007)
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