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Journal ArticleDOI

Population Genetics of Agave cocui: Evidence for Low Genetic Diversity at the Southern Geographic Limit of Genus Agave

01 May 2011-Journal of Heredity (Oxford University Press)-Vol. 102, Iss: 3, pp 306-314

TL;DR: Level of allozyme diversity and population structure of Agave cocui, the species at the southern limit of distribution of the genus, and one of the lowest values of genetic variability are presented, suggesting that human impact represents a significant threat to the available genetic pool that this species possesses in the region.

AbstractThe Agave genus embraces many species with outstanding ecological and economic importance in the arid regions of the Americas. Even though this genus covers a broad geographic distribution, our knowledge on the population genetics of species is concentrated in taxa located in North America. Recently, it has been demonstrated that plant domestication decreases levels of genetic diversity in managed populations and increases population structure with respect to wild populations. We examined levels of allozyme diversity (N = 17 loci) and population structure of Agave cocui, the species at the southern limit of distribution of the genus. We sampled 7 wild populations (N = 30-35 individuals per population) representative of the geographic distribution of the species in Venezuela. Among the agaves studied, A. cocui has some of the lowest estimates of genetic diversity (H(e)[species] = 0.059, H(e)[population] = 0.054) reported until present. We propose that this condition is probably linked to the recent origin of this species in arid and semiarid regions of Colombia and Venezuela, probably through one or a few founder events. The lowest estimates of genetic diversity were associated with small populations in very restricted arid patches; but also with overexploitation of rosettes for production of fermented drinks and fibers. Santa Cruz de Pecaya, one of the 2 centers of economic use of agaves in northwestern Venezuela presented one of the lowest values of genetic variability, a sign suggesting that human impact represents a significant threat to the available genetic pool that this species possesses in the region.

Topics: Population (57%), Genetic diversity (57%), Gene pool (56%), Agave (55%), Population genetics (55%)

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Citations
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Journal ArticleDOI
TL;DR: This work describes studies in 22 Agave species using different genetic markers and identifies some species that should be subject to special conservation genetic efforts, in particular the endangered A. victoriae-reginae and both wild populations and landraces of A. angustifolia.
Abstract: Mexico is a megadiverse country, but less than 54 % of its original vegetation still remains. In particular Mexican deserts and arid and semiarid ecosystems harbor a large number of endemic taxa, and the genus Agave is an outstanding example. Agave is one of the largest genera of the Mexican flora, including a total estimated number of 200 species, 74 % of them endemic to the country. Agave is also one of the Mexican plant genera with more population genetic studies. We describe here studies in 22 Agave species using different genetic markers. For the genus we found on average a high level of genetic variation, H s = 0.19, and a low genetic differentiation, F st = 0.15. We identify some species that should be subject to special conservation genetic efforts, in particular the endangered A. victoriae-reginae and both wild populations and landraces of A. angustifolia, including the cultivated A. tequilana.

32 citations


Cites background or methods from "Population Genetics of Agave cocui:..."

  • ...An isolation by distance analysis using Fst/(1−Fst) as an estimate of the genetic distance between pairs of populations vs. the ln of the geographic distance, indicated a positive correlation with a r2=0.187 (Figueredo & Nassar, 2011)....

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  • ...The Nei’s genetic distances were accordingly low, with an average of D=0.005 and a range between 0.001 and 0.016 (Figueredo & Nassar, 2011)....

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  • ...The population genetics of the species was described by Figueredo and Nassar (2011) using 17 isoenzymatic loci and seven populations, including 30 to 35 plants per population and covering a large area, of ca. 240,000 km2....

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Journal ArticleDOI
TL;DR: The data indicate that these species are not genetically eroded in general, and that they retain their historical patterns of diversity inside populations, and three genetically distinct populations are identified where conservation efforts should be a priority.
Abstract: Agave cupreata and Agave potatorum are semelparous species distributed on dry tropical forests in south Mexico. Extraction of reproductive individuals for spirits production has caused a decline of wild populations and has raised concerns about their long-term conservation. We assess the degree of genetic erosion of exploited populations and provide population genetics baseline data for developing sustainable use strategies of these species. ISSRs (Inter Simple Sequence Repeats, dominant nuclear markers associated to microsatellites) were used to analyze five populations of each species throughout their distribution range. We found high levels of variation (P > 80%; H > 0.30) and moderate to high differentiation (A. potatorum θ = 0.120; A. cupreata θ = 0.172). Isolation by distance was significant in A. cupreata. Our data indicate that these species are not genetically eroded in general, and that they retain their historical patterns of diversity inside populations. Three genetically distinct populations are identified where conservation efforts should be a priority. Our results are discussed in relation to the in situ reinforcement of populations based on seeds propagation, in contrast to micropropagation practices that may threaten the genetic diversity of the species studied considering previous reports on genetic bottlenecks and inbreeding depression in Agave.

25 citations



Journal ArticleDOI
TL;DR: Bayesian analysis indicated that genetic clusters best fit with the corresponding habitats where populations grow, and natural mechanisms of gene flow and movement of agave propagules among populations by people explain these patterns.
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 gra- dient 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 ¼ 0.707) and moderate genetic structure (FST ¼ 0.112). No differences were found in levels of genetic diversity among wild (He ¼ 0.704), silviculturally managed (He ¼ 0.733) and cultivated (He ¼ 0.698) popula- tions. Bayesian analysis indicated that five genetic clusters best fit the data, with genetic groups corresponding to habi- tats where populations grow rather than to management. Migration rates ranged from zero between two populations to markedly high among others (M ¼ 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 popu- lations. The slight differentiation associated with management indicates that domestication is in an incipient stage.

14 citations


Cites background from "Population Genetics of Agave cocui:..."

  • ...Often, the highest levels of genetic diversity have been found in the centre of origin, and levels decrease as long as the distance increases until the extremes of the area of distribution (Eckert et al. 2008; Figueredo and Nassar 2011; Parra et al. 2015)....

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Journal ArticleDOI
TL;DR: The study suggests slight effects of management on genetic diversity of A. potatorum, apparently related to alterations of reproductive biology and pollination patterns, and Bayesian analysis indicated two genetic groups.
Abstract: Agave potatorum is a wild endemic species of Mexico. Its stems are used for mescal production, which cancels sexual reproduction. Agaves extraction from forests decreases their reproductive success and demographic performance. We evaluated patterns of genetic diversity and structure of wild populations under and without extraction in order to identify effects of its use and actions required for conserving genetic variation. This study was conducted with seven SSR markers in 12 populations representing the entire distribution area of the species. Standard parameters of genetic diversity, differentiation, structure and genetic similarity of populations were calculated and analyzed. The populations studied showed intermediate to high genetic diversity (H e = 0.36–0.64), compared with other Agave species so far studied. The wild category was the most diverse (H T = 0.87), but without significant differences with respect to populations under extraction (H T = 0.72), and two germplasm banks sampled (H T = 0.69). High structure among populations (Φ PR = 0.38) and inbreeding levels (F IS = 0.26, F IT = 0.55) were identified; a 3 % of genetic diversity being distributed among management status where germplasm banks represent a genetic pool with incipient divergence from the other categories. Bayesian analysis indicated two genetic groups. Our study suggests slight effects of management on genetic diversity of A. potatorum, apparently related to alterations of reproductive biology and pollination patterns.

9 citations


Additional excerpts

  • ...Figueredo and Nassar 2011)....

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References
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"Population Genetics of Agave cocui:..." refers background or methods in this paper

  • ...The dendrogram obtained using this procedure was created with the program MEGA v. 4.0 (Tamura et al. 2007) and helped to understand the genetic relationship among populations....

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"Population Genetics of Agave cocui:..." refers background in this paper

  • ...Nei’s parameters of genetic diversity (Nei 1973, 1977) were estimated for each polymorphic locus, including total genetic diversity (HT), mean genetic diversity within populations (HS), and the proportion of genetic diversity due to differences among populations (GST 5 (HT HS)/HT)....

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