Population Genetics of Agave cocui: Evidence for Low Genetic Diversity at the Southern Geographic Limit of Genus Agave
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.
Abstract: The 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.
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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.
41 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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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.
36 citations
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.
20 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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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.
16 citations
Additional excerpts
...Figueredo and Nassar 2011)....
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References
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TL;DR: The phylogenetic limits of Agave sensu lato are examined and the potential for both monocarpy and the evolution of a generalist pollination system, largely dependent on nectarivorous bat species, as possible driving factors in the radiation of the group are discussed.
Abstract: The Agave (Agavaceae) are keystone species of semiarid to arid regions where the geographic center of origin is Mexico but whose populations spread from the southwestern U.S. through Central America, the Caribbean, and into northern South America. Our analyses indicate that Agave is a young genus, between 7.8 and 10.1 million years old, and yet it harbors the most species of any genera in the family. Of the eight genera in the family, Agave is paraphyletic with respect to three of them, and these four genera are often grouped into a genus termed Agave sensu lato, which harbors 208 of the 293 recognized species in the Agavaceae. In this article, we examine the phylogenetic limits of Agave sensu lato and present analyses elucidating the origin and rate of speciation in the group. These analyses lead to some new insights into the phylogenetic limits of Agave, indicate an estimated age of the family between 20 and 26 million years and an age of the Agave sensu lato of ≤10 million years. Furthermore, we estimate a high mean per-lineage rate of diversification for the genus and find that rates of speciation were significantly elevated between 8 and 6 million years ago and then again between 3 and 2.5 million years ago. We discuss the potential for both monocarpy and the evolution of a generalist pollination system, largely dependent on nectarivorous bat species, as possible driving factors in the radiation of the group.
223 citations
"Population Genetics of Agave cocui:..." refers background in this paper
...The genus Agave also appeared and diversified in Mexico 8 to 10 Ma (Good-Avila et al. 2006)....
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...The Agavaceae originated and radiated in Mexico 20–26 million years ago (Ma) (Garcı́a-Mendoza and Galván 1995; Good-Avila et al. 2006)....
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...The Agavaceae originated and radiated in Mexico 20–26 million years ago (Ma) (Garcı́a-Mendoza and Galván 1995; Good-Avila et al. 2006)....
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Book•
01 Jan 2002
TL;DR: This book presents a meta-anatomy of the Cacti of Mesoamerican Domestication and Diffusion, and some of the mechanisms behind its domestication and distribution, which are described in more detail in the preface.
Abstract: List of Contributors Preface 1. Evolution and Systematics Robert S. Wallace and Arthur C. Gibson 2. Shoot Anatomy and Morphology Teresa Terrazas Salgado and James D. Mauseth 3. Root Structure and Function Joseph G. Dubrovsky and Gretchen B. North 4. Environmental Biology Park S. Nobel and Edward G. Bobich 5. Reproductive Biology Eulogio Pimienta-Barrios and Rafael F. del Castillo 6. Population and Community Ecology Alfonso Valiente Banuet and Hector Godinez-Alvarez 7. Consumption of Platyopuntias by Wild Vertebrates Eric Mellink and Monica E. Riojas-Lopez 8. Biodiversity and Conservation Thomas H. Boyle and Edward F. Anderson 9. Mesoamerican Domestication and Diffusion Alejandro Casas and Giuseppe Barbera 10.Cactus Pear Fruit Production Paolo Inglese, Filadelfio Basile, and Mario Schirra 11. Fruits of Vine and Columnar Cacti Avinoam Nerd, Noemi Tel-Zur, and Yosef Mizrahi 12. Forage, Fodder, and Animal Nutrition Ali Nefzaoui and Hichem Ben Salem 13. Nopalitos, Mucilage, Fiber, and Cochineal Carmen Saenz-Hernandez, Joel Corrales-Garcia, and Gildardo Aquino-Perez 14. Insect Pests and Diseases Helmuth G. Zimmermann and Giovanni Granata 15. Cactus Breeding and Biotechnology Brad Chapman, Candelario Mondragon Jacobo, Ronald A. Bunch, and Andrew H. Paterson Index
219 citations
TL;DR: L'electrophorese sur gel d'amidon constitue une methode puissante and economiquement abordable pour estimer la variabilite genetique des especes vegetales et de leurs populations.
Abstract: L'electrophorese sur gel d'amidon constitue une methode puissante et economiquement abordable pour estimer la variabilite genetique des especes vegetales et de leurs populations. Les loci d'alloenzymes representent des caracteres typiquement monogeniques, qui se recombinent de facon independante et affichent des alleles co-dominants. Des tailles d'echantillon variant de 30-50 individus analyses pour 10-20 loci polymorphes s'averent suffisantes pour caracteriser de facon adequate la diversite genetique d'une population et evaluer comment la diversite genetique se repartit parmi les populations. Les parametres qui devraient etre utilises sont le pourcentage de loci polymorphes (P), le nombre moyen d'alleles par locus polymorphe (AP), l'heterozygotie theorique (diversite genetique, H c ), la valeur G ST de Nei, l'identite genetique (I) et la distance genetique (D). Les auteurs presentent des exemples, en plus de faire un sommaire des tests qui permettent d'evaluer la confiance statistique des estimations de parametres.
162 citations
148 citations
Book•
01 Jan 1992
TL;DR: This checklist gives information on a number of species of Cactaceae included in Appendices I and II of CITES regarding their identification, nomenclature and distribution.
Abstract: This checklist gives information on a number of species of Cactaceae included in Appendices I and II of CITES regarding their identification, nomenclature and distribution. It is a first step towards a better implementation of CITES for this group of plants.
136 citations
"Population Genetics of Agave cocui:..." refers background in this paper
...Agave cocui (Trelease) occupies the southeastern limits of distribution of the genus in northern South America and nearby islands (Garcı́a-Mendoza 2002)....
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...We hypothesize that this condition could be related to its recent origin in northern South America, probably through one or few founder events, and differences observed in genetic variability among populations should be determined by a combination of ecological and anthropogenic factors....
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...Central American countries have one or 2 species of Stenocereus, but only 1 species reached northern South America (Hunt 1999)....
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...We think that humans are probably the main dispersal agents responsible for moving genes of A. cocui among populations and promoting colonization events during the time people have used this plant in northern South America....
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...Species of this genus distributed in northern South America are most likely the result of the most recent colonization events, either through the Caribbean or through Central America, which began after species radiated in Mexico....
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