Diversity and spatial genetic structure of a natural population of Theobroma speciosum (Malvaceae) in the Brazilian Amazon (original) (raw)
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Heredity, 2011
Understanding the mating patterns of populations of tree species is a key component of ex situ genetic conservation. In this study, we analysed the genetic diversity, spatial genetic structure (SGS) and mating system at the hierarchical levels of fruits and individuals as well as pollen dispersal patterns in a continuous population of Theobroma cacao in Pará State, Brazil. A total of 156 individuals in a 0.56 ha plot were mapped and genotyped for nine microsatellite loci. For the mating system analyses, 50 seeds were collected from nine seed trees by sampling five fruits per tree (10 seeds per fruit). Among the 156 individuals, 127 had unique multilocus genotypes, and the remaining were clones. The population was spatially aggregated; it demonstrated a significant SGS up to 15 m that could be attributed primarily to the presence of clones. However, the short seed dispersal distance also contributed to this pattern. Population matings occurred mainly via outcrossing, but selfing was observed in some seed trees, which indicated the presence of individual variation for self-incompatibility. The matings were also correlated, especially within (r p(m) ¼ 0.607) rather than among the fruits (r p(m) ¼ 0.099), which suggested that a small number of pollen donors fertilised each fruit. The paternity analysis suggested a high proportion of pollen migration (61.3%), although within the plot, most of the pollen dispersal encompassed short distances (28 m). The determination of these novel parameters provides the fundamental information required to establish long-term ex situ conservation strategies for this important tropical species.
Forest Ecology and Management, 2020
The aims of this study were to investigate the intrapopulation spatial genetic structure (SGS) of a preserved Swietenia macrophylla population in a managed forest in Southwestern Amazon, in Acre state, Brazil, and assess the genetic parameters that underlie the conceptual framework that guides conservation and management strategies. The study was conducted in Annual Production Unit (APU) 3, where 83 adult trees (DBH ≥ 40 cm) were mapped (1650 ha). The diameter at breast height (DBH) was measured and the vascular exchange was sampled. Leaf tissues were collected from 187 juvenile individuals within a radius of 20 m of adults. The population presented high heterozygosity (H o) for adult (0.767) and juvenile (0.763) individuals, but significantly high allelic richness (R) and significantly lower fixation index (F) in adults (R = 10.3, F = 0.048) than juveniles (R = 9.3, F = 0.119). The F value significantly higher for juveniles, suggesting selection against inbred individuals between juvenile and adult life stages. SGS was detected for adults up to 300 m. Mating was mainly through outcrossing (0.97-1.0), but some crossing occurred among related trees (0.02-0.16) and were correlated (r pm = 0.06-0.22), indicating a mean effective number of pollen donors ranging from 4.5 to 18.2. Pollen dispersal distances reached 3905 m (mean of 1472 m), and mean effective pollination neighbor area of 792 ha. The effective population size (N e) within family (2.73) was lower than expected for random mating populations. The number of trees (m) required for seed collection was estimated at 55 non-inbreed and not related trees to each other. The core collection consisted of 42 (50.6%) adults across the area. These individuals should be included in seed collection as they represent 100% of the total detected genetic diversity. The inclusion of S. macrophylla on the list of species available for exploitation is not indicated, because the species requires cross breeding for its maintenance and logging reduce the N e and may negatively impact the pattern of genetic diversity. These will significantly increase the risk of genetic erosion and population extinction due to a lack of adaptive ability. Adults serve as pollen donors that ecologically and genetically contribute to the maintenance of gene flow and N e. Because it is recognized as a threatened species worldwide, and due to the fact that in areas of natural occurrence the species presents low-density and shows difficulty establishing natural regeneration, we recommend that S. macrophylla be protected from selective logging.
Ecology and Evolution
Euterpe precatoria, known as açaí do Amazonas, is a regionally important palm of the Amazon rainforest for the fruit production through extractive agriculture. Little information is available with regard to genetic diversity, gene flow, and spatial genetic structure (SGS) of açaí populations, which are essential for the use, management, and conservation of genetic resources of the species. This research aimed to assess the genetic diversity, inbreeding level, SGS, and gene flow in four ontogenetic stages of a natural E. precatoria population in the Brazilian Amazon, based on 18 microsatellite loci. The study was carried out in a natural population dispersed in an area of about 10 ha. Leaf tissues of 248 plants were mapped and sampled and classified into four ontogenetic stages: reproductive (59), immature (70), young (60), and seedling (59). Genetic diversity indices were high for all ontogenetic stages. The fixation index (F) for all ontogenetic stages was not significantly different from zero, indicating the absence of inbreeding. A significant SGS was found for all ontogenetic stages (68-110 m), indicating seed dispersal over short distances. Paternity analysis detected pollen immigration of 39.1%, a selfing rate of 4.2%, and a mean pollen dispersal distance within the population of 531 m. The results indicate substantial allele input in the population via pollen immigration, contributing to the maintenance of the genetic
Molecular Ecology, 2003
Mahogany (Swietenia macrophylla, Meliaceae) is the most valuable and intensively exploited Neotropical tree. No information is available regarding the genetic structure of mahogany in South America, yet the region harbours most of the unlogged populations of this prized hardwood. Here we report on the genetic diversity within and the differentiation among seven natural populations separated by up to 2100 km along the southern arc of the Brazilian Amazon basin. We analysed the variation at eight microsatellite loci for 194 adult individuals. All loci were highly variable, with the number of alleles per locus ranging from 13 to 27 (mean = 18.4). High levels of genetic diversity were found for all populations at the eight loci (mean HE = 0.781, range 0.754–0.812). We found moderate but statistically significant genetic differentiation among populations considering both estimators of FST and RST, θ = 0.097 and ρ = 0.147, respectively. Estimates of θ and ρ were significantly greater than zero for all pairwise population comparisons. Pairwise ρ-values were positively and significantly correlated with geographical distance under the isolation-by-distance model. Furthermore, four of the populations exhibited a significant inbreeding coefficient. The finding of local differentiation among Amazonian mahogany populations underscores the need for in situ conservation of multiple populations of S. macrophylla across its distribution in the Brazilian Amazon. In addition, the occurrence of microgeographical genetic differentiation at a local scale indicates the importance of maintaining populations in their diverse habitats, especially in areas with mosaics of topography and soil.
Genetic Structure in Populations of Euterpe precatoria Mart. in the Brazilian Amazon
Frontiers in Ecology and Evolution, 2021
Euterpe precatoriais a palm tree belonging to the Arecaceae family, occurring in Western and Central Brazilian Amazonia. Its fruit, which is very appreciated in the Amazon region, produces pulp that is consumed in fresh form. Its production is carried out almost exclusively by extractive farmers. In order to establish adequate strategies to sustain this genetic resource, we need knowledge about the diversity and genetic structure in natural populations. This study aimed to evaluate the influence of geographic distance on genetic structure in the main extractive populations ofE. precatoriain the Brazilian Amazon. Leaves from 377 plants were collected in 19 populations located in 16 municipalities in the State of Amazonas and three in the State of Rondônia. Twelve microsatellite loci were used to genotype the plants. The diversity and genetic structure among populations were estimated. The average number of alleles per locus was 5.97. The observed heterozygosity means (HO) were higher...
Tree Genetics & Genomes, 2012
We present a case study of the relationship between spatial genetic structure (SGS) and age structure in Protium spruceanum (Burseraceae), an insect-pollinated, mass-fruiting, and secondary bird-dispersed tree, as determined through variation in allozyme loci. Using ten polymorphic loci, we investigated spatial and temporal patterns of a genetic structure within a 40 m×60 m plot in a small (1.0 ha) fragment of Atlantic Rainforest to investigate the processes shaping the distribution of genetic diversity. Individuals (n0345) from seedlings to adults were grouped and analyzed in four diameter classes. The results showed a high average level of genetic diversity (H e 00.438), but genetic diversity parameters did not vary significantly among cohorts. The spatial distribution pattern analysis of individuals showed significant levels of aggregation among small-and medium-diameter classes and random distribution among the highest diameter class, likely due to processes of competitive thinning. There was an association between demographic and SGS at short distances (less than 10 m) which is likely the consequence of restricted seed dispersal. The degree of SGS decreased across small-to large-diameter classes. We inferred that limited seed dispersal and subsequent density-dependent mortality from the family clusters are responsible for the observed changes in fine-scale SGS across different demographic classes.
Biochemical Systematics and Ecology, 2015
Worldwide, Seasonally Dry Tropical Forests (SDTF) are among the least known and most degraded vegetation types. Cavanillesia arborea (Malvaceae) is an endemic dry forest tree that is bat-pollinated and the seeds are wind-dispersed. The present study sought to characterize the spatial genetic structure (SGS) in natural populations of C. arborea growing in SDTF fragments in Minas Gerais State, Brazil, using ISSR molecular markers. Seven ISSR primers generated 81 polymorphic loci in 175 individuals. In three populations (FU, MO and PC), we found random distributions of genotypes, while two populations (JAN and MV) showed SGS in their first distances classes (171 m and 17 m, respectively), with significant kinship (Sp) values (0.0189 and 0.0005 respectively; P < 0.05). Sp values for these populations indicate that the effects of kinship can be minimized by collecting seeds from distance classes beyond the species' first distance class. The continuous anthropogenic impacts on remnant tree populations, low species densities, and the observed genetic structure, all indicate the need to preserve large areas of dry forest vegetation for conservation purposes.
Genetics and Molecular Biology, 2012
The Atlantic Forest is one of the most diverse ecosystems in the world and considered a hotspot of biodiversity conservation. Dalbergia nigra (Fabaceae) is a tree endemic to the Brazilian Atlantic Forest, and has become threatened due to overexploitation of its valuable timber. In the present study, we analyzed the genetic diversity and fine-scale spatial genetic structure of D. nigra in an area of primary forest of a large reserve. All adult individuals (N = 112) were sampled in a 9.3 ha plot, and genotyped for microsatellite loci. Our results indicated high diversity with a mean of 8.6 alleles per locus, and expected heterozygosity equal to 0.74. The co-ancestry coefficients were significant for distances among trees up to 80 m. The Sp value was equal to 0.017 and indirect estimates of gene dispersal distances ranged from 89 to 144 m. No strong evidence of bottleneck or effects of human-disturbance was found. This study highlights that long-term efforts to protect a large area of Atlantic Forest have been effective towards maintaining the genetic diversity of D. nigra. The results of this study are important towards providing a guide for seed collection for ex-situ conservation and reforestation programmes of this threatened species.
Genetic structure of Bertholletia excelsa populations from the Amazon at different spatial scales
Conservation Genetics, 2015
Population genetic structure and genetic diversity levels are important issues to understand population dynamics and to guide forest management plans. The Brazil nut tree (Bertholletia excelsa Bonpl.) is an endemic species, widely distributed through Amazonian upland forests and also an important species for the local extractive economy. Our aim was to analyze the genetic structure of Brazil nut trees at both fine and large scales throughout the Amazon Basin, contributing to the knowledge base on this species and to generate information to support plans for its conservation. We genotyped individuals from nine sites distributed in five regions of the Brazilian Amazon using 11 microsatellite loci. We found an excess of heterozygotes in most populations, with significant negative inbreeding coefficients (f) for five of them and the finescale structure, when present, was very small. These results, as a consequence of self-incompatibility, indicate that conservation plans for B. excelsa must include the maintenance of genetic diversity within populations to ensure viable amounts of seeds for both economic purposes and for the local persistence of the species.
Conservation Genetics, 2006
A sample of 94 accessions of Theobroma cacao L. (cacao), representing four populations from the Brazilian Amazon (Acre, Rondoˆnia, lower Amazon and upper Amazon) were analyzed using microsatellite markers to assess the genetic diversity and the natural population structure. From the 19 microsatellite loci tested, 11 amplified scorable products, revealing a total of 49 alleles, including two monomorphic loci. The Brazilian upper Amazon population contained the largest genetic diversity, with the most polymorphic loci, the highest observed heterozygosity; and the majority of rare alleles, thereby this region might be considered part of the center of diversity of the species. The observed heterozygosity for all the Brazilian populations (H o =0.347) was comparable with values reported for other similar upper Amazon Forastero cacao populations, with the Acre and Rondoˆnia displaying the lowest values. The lower Amazon population, traditionally defined as highly homozygous, presented an unexpectedly high observed heterozygosity (H o =0.372), disclosing rare and distinct alleles, with large identity with the upper Amazon population. It was hypothesized that part of the lower Amazon population might derive from successive natural or intentional introduction of planting material from other provenances, mainly upper Amazon. Most of the loci exhibited a lower observed heterozygosity than expected, suggesting that self-pollination might be more common than usually assumed in cacao, but excess of homozygotes might also derive from sub-grouping (Wahlund effect) or from sampling related individuals. Most of the gene diversity was found to occur within groups, with small differentiation between the four Brazilian Amazon populations, typical of species with high gene flow.