Genetic diversity in populations of African mahogany (Khaya grandioliola C. DC.) introduced in Brazil (original) (raw)
Related papers
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.
Forest Ecology and Management, 2008
Big-leaf mahogany (Swietenia macrophylla King, Meliaceae) is the most valuable widely traded timber species from the Neotropics. Mahogany has been severely overexploited throughout its natural range, which stretches from southern Mexico through Central and South America as far south as the Bolivian Amazon. We investigated effects of selective logging on the genetic diversity of a mahogany population in eastern Amazonia. Using eight hypervariable microsatellite loci, we estimated the number of alleles per locus (A), mean expected and observed heterozygosity (H e , H o ), the number of distinct multilocus genotypes (G o ), and the inbreeding coefficient ( f) for pre-and post-logging cohorts (adults and seedlings) collected over identical spatial scales. We found a significant reduction in the number of alleles, observed heterozygosity, and distinct multilocus genotype number in the post-compared to the pre-logging cohort. The loss of genetic diversity is likely to have occurred due to a reduction in the effective population size as a consequence of logging, which leads to the loss of alleles and limits mating possibilities. The results raise concerns about the conservation genetics of logged mahogany populations where a high proportion of adults are removed from the system. We suggest initiatives to promote the maintenance of genetic diversity as an integral part of the production system, allowing genetically sustainable use of this valuable timber resource. #
Genetic Variation in Tropical Tree Species and Plantations: A Review
Open Journal of Forestry, 2022
The global efforts to restore tropical forests and their productive and ecological functions through plantation forestry largely depend on the available genetic variation in the tree species used to establish the plantations. However, there is limited information on the levels and trends of the genetic variation and variability of different plantation tree species in the tropics. Therefore, this study reviews several marker-based studies that have investigated genetic variation. Most of the top economic species like Eucalyptus tereticornis and Mansonia altissima are attributed to low levels of genetic diversity, while others like Pinus caribaea and Swietenia macrophylla still exhibit high expected heterozygosity across different populations. However, the levels of genetic diversity assessed may depend on the markers used. Microsatellites, i.e., simple sequence repeats (SSRs), mostly give higher estimates when compared to other polymerase chain reaction-based markers. Other factors that typically contribute to the directional pattern of genetic variation in tropical tree species and populations include their distribution, density, seed dispersal, succession, and reproduction. Also, anthropogenic impacts like logging and fragmentation have contributed to the vast genetic base reduction of many tropical species and populations. Having adequate genetic variation within the plantation populations is significant in improving their fitness, resilience, fecundity, productivity, and other ecological functions. It also provides a basis for tree improvement and breeding in plantation forests. Although clonal forestry is becoming widespread and considered highly productive, it is attributed to specific economic, technical, and ecological risks, such as the increased spread of pests and diseases. Therefore, further discussions and recommendations to maximise genetic diversity in tropical (clonal) plantations are provided.
Conservation Genetics, 2019
The genus Khaya includes some of the highest-value timber species in natural forests in Africa, which are under heavy exploitation pressure. Genetic identification of Khaya species is important to confirm the taxonomic classification for biodiversity conservation purposes and as a forensic tool aiding law enforcement in the fight against illegal logging. We collected samples from a total of 2222 trees belonging to five or six (depending on classification) different Khaya species (K. ivorensis, K. anthotheca/K. nyasica, K. grandifoliola, K. senegalensis, K. madagascariensis). Representative sampling was conducted over the natural ranges of all sampled Khaya species, in humid tropical forest and savanna zones. We genotyped individuals based on 101 molecular markers (67 nuclear, 11 chloroplast and 22 mitochondrial SNPs, 1 chloroplast indel). Bayesian clustering produced three main genetic groups assigning all K. ivorensis and all K. senegalensis trees, respectively, in two different clusters and all remaining individuals in a third cluster. Genetic self-assignment tests with all 101 SNPs had success rates of 97-100% for all species except for K. nyasica and K. madagascariensis, which could not be clearly distinguished from each other. A success rate for species identification nearly as high was observed using a subset of 15 highly differentiated SNPs. There was only very little evidence for hybridization among species and the vast majority (> 97%) of individuals were assigned to the same species group as identified based on morphological characters.
Acta Amazonica, 2008
Rosewood (Aniba rosaeodora Ducke, Lauraceae) is an Amazonian evergreen tree and a source of the purest linalool, the main component of its essential oil, which is very valuable in the international perfumery market. After decades of over-exploitation it is currently considered as threatened. We evaluated the genetic diversity and its distribution in four populations in Central Amazonia. Thirty-five reliable RAPD markers were generated, of which 32 were polymorphic (91.4%). Variation was higher within the populations (76.5%; p < 0.0001) and geographic distribution contributed to population differentiation (23.4%; p < 0.0001). The Amazon River had a small influence on gene flow (3.3%; p < 0.0001), but we identified evidence of gene flow across the river. There were significant differences in marker frequencies (p < 0.05), in agreement with the low gene flow (Nm = 2.02). The correlation between genetic distance and gene flow was - 0.95 (p = 0.06) and between geographic dist...
Biological Conservation
To support the long-term ecological viability of restoration projects, it is necessary to reach adequate levels of genetic diversity in spontaneously recolonizing and reintroduced populations. The importance of genetic diversity in the long-term viability of populations is acknowledged, but still poorly monitored in restoration projects. This study aimed to estimate the genetic diversity and inbreeding levels of populations of a tree species widely used in restoration projects in the Atlantic Forest of Brazil, Centrolobium tomentosum, exploring the potential of active restoration in successfully reestablishing populations with higher chances of long-term perpetuation in agricultural landscapes. We used both nuclear and chloroplast microsatellite markers to assess genetic parameters in juveniles and adult individuals in two high-diversity restoration plantations (28 and 60 years old), one disturbed fragment, and one large and well conserved protected area. We observed similar levels of genetic diversity and inbreeding, for juveniles and adults, in both restored and natural populations. Surprisingly, haplotype diversity was higher in restoration sites. We also found private alleles in juveniles in both restoration areas, and this is evidence of gene flow between restored and neighboring natural populations. However, we observed negative effects of inbreeding on the effective population size of populations from the disturbed natural remnant and restoration areas. These results provide evidence of the capacity of restoration plantations for recovering high levels of genetic diversity and the importance of maintaining large and wellconserved forest remnants to be used as seed sources for restoration efforts.
Australian Journal of Crop Science
Morphometric studies of fruits and forest seeds may indicate the presence of variability among individuals of the same species. The objective of this study was to investigate the morphometric diversity of fruits and seeds of Swietenia macrophylla in 20 individuals belong to the Parakanã Indigenous Land, PA, Brazil. The following characteristics of the fruits, wingless seeds, and seeds without testa of the 20 trees were evaluated. Analysis of variance was performed on the collected data, followed by test of the means by Scott-Knott test. Genetic dissimilarity was assessed through means of the Unweighted Pair Group Method with Arithmetic Mean (UPGMA) grouping technique and canonical variables (CV). The results indicate high phenotypic diversity among mahogany fruits and seeds and the grouping of trees regardless is of the location of the indigenous village. Thus, mahogany trees have high genetic potential for germplasm conservation, seed harvesting, and breeding programs.
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.
Molecular Ecology, 2003
While microsatellites have been used to examine genetic structure in local populations of Neotropical trees, genetic studies based on such high-resolution markers have not been carried out for Mesoamerica as a whole. Here we assess the genetic structure of the Mesoamerican mahogany Swietenia macrophylla King (big-leaf mahogany), a Neotropical tree species recently listed as endangered in CITES which is commercially extinct through much of its native range. We used seven variable microsatellite loci to assess genetic diversity and population structure in eight naturally established mahogany populations from six Mesoamerican countries. Measures of genetic differentiation ( F ST and R ST ) indicated significant differences between most populations. Unrooted dendrograms based on genetic distances between populations provide evidence of strong phylogeographic structure in Mesoamerican mahogany. The two populations on the Pacific coasts of Costa Rica and Panama were genetically distant from all the others, and from one another. The remaining populations formed two clusters, one comprised of the northern populations of Mexico, Belize and Guatemala and the other containing the southern Atlantic populations of Nicaragua and Costa Rica. Significant correlation was found between geographical distance and all pairwise measures of genetic divergence, suggesting the importance of regional biogeography and isolation by distance in Mesoamerican mahogany. The results of this study demonstrate greater phylogeographic structure than has been found across Amazon basin S. macrophylla . Our findings suggest a relatively complex Mesoamerican biogeographic history and lead to the prediction that other Central American trees will show similar patterns of regional differentiation.
We review here the scale of neutral and adaptive genetic variation of mahogany (Swietenia spp.), one of the most valuable tree species in the world, and relate this information directly to provenance performance, and seed transfer and sourcing recommendations. Further, we explore a series of scientific issues directly related to critical day-to-day management of mahogany, giving guidelines to maximise genetic diversity outcomes in natural, remnant, sustainably harvested, and/or restored forest landscapes. The study concludes that conservation and sustainable management of mahogany genetic resources cannot be simply defined in terms of one-size-fits-all solutions, and requires local community involvement to prevent illegal logging and ensure mutual benefit. Landscape level strategies for the effective management of mahogany trees outside of forests urgently need to be developed, together with strategies to promote the benefits of different agroforestry practices. There is also a requirement for conservation planners to consider that trees found outside protected areas have a role in the conservation. In wide-ranging species, promoting international collaboration for collecting, characterising, and conserving genetic resources is vital as international consensus is needed to streamline phytosanitary procedures, to facilitate the exchange of forest reproductive material, and assist genetic resource conservation efforts.