Genetic diversity, structure and adaptation in Mesoamerican mahogany - implications for genetic resource management and conservation (original) (raw)
Related papers
Genetic resources and conservation of Mahogany in Mesoamerica
Heredity, 2010
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.
Mahogany as a genetic resource
Botanical Journal of The Linnean Society, 1996
The development of a strategy for the sustainable management and conservation of mahogany is an urgent priority. Such a strategy should be based upon clear information about the extent of genetic differentiation within and between populations, and on an understanding of the processes maintaining this variation. At present, such information is very limited for mahogany. Preliminary data are presented from two genetic tests of Szmitaia muoophyllu King (Meliaceae), indicating significant differences between provenances and half-sib progenies in both growth and form characteristics. In addition, the use of molecular markers for the characterization of genetic resources of mahogany is discussed. On the basis of the results available, the impacts of deforestation and logging activities on genetic resources are evaluated. Although both deforestation and selective logging may deplete genetic resources, no quantitative information on the extent of such depletion in mahogany is currently available. Additional research is therefore required before clear guidelines can be provided for the sustainable management of mahogany.
Heredity, 1999
Swietenia macrophylla King, a timber species native to tropical America, is threatened by selective logging and deforestation. To quantify genetic diversity within the species and monitor the impact of selective logging, populations were sampled across Mesoamerica, from Mexico to Panama, and analysed for RAPD DNA variation. Ten decamer primers generated 102 polymorphic RAPD bands and pairwise distances were calculated between populations according to Nei, then used to construct a radial neighbour-joining dendrogram and examine intra-and interpopulation variance coecients, by analysis of molecular variation (AMOVA AMOVA). Populations from Mexico clustered closely together in the dendrogram and were distinct from the rest of the populations. Those from Belize also clustered closely together. Populations from Panama, Guatemala, Costa Rica, Nicaragua and Honduras, however, did not cluster closely by country but were more widely scattered throughout the dendrogram. This result was also re¯ected by an autocorrelation analysis of genetic and geographical distance. Genetic diversity estimates indicated that 80% of detected variation was maintained within populations and regression analysis demonstrated that logging signi®cantly decreased population diversity (P 0.034). This study represents one of the most wide-ranging surveys of molecular variation within a tropical tree species to date. It oers practical information for the future conservation of mahogany and highlights some factors that may have in¯uenced the partitioning of genetic diversity in this species across Mesoamerica.
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. #
Heredity, 2003
Fine-scale structure of genetic diversity and gene flow were analysed in three Costa Rican populations of mahogany, Swietenia macrophylla. Population differentiation estimated using AFLPs and SSRs was low (38.3 and 24%) and only slightly higher than previous estimates for Central American populations based on RAPD variation (20%). Significant finescale spatial structure was found in all of the surveyed mahogany populations and is probably strongly influenced by the limited seed dispersal range of the species. Furthermore, a survey of progeny arrays from selected mother trees in two of the plots indicated that most pollinations involved proximate trees. These data indicate that very little gene flow, via either pollen or seed, is occurring between blocks of mahogany within a continuous or disturbed forest landscape. Thus, once diversity is removed from a forest population of mahogany, these data suggest that recovery would be difficult via seed or pollen dispersal, and provides an explanation for mahogany's apparent susceptibility to the pressures of logging. Evidence is reviewed from other studies of gene flow and seedling regeneration to discuss alternative extraction strategies that may maintain diversity or allow recovery of genetic resources.
Forest Ecology and …, 2008
Stocks of the valuable big-leaf mahogany (Swietenia macrophylla King) are declining, and trials for growth and pest resistance are needed to select material for plantations. Seeds were collected from 67 open-pollinated trees from five provenances in the Yucatan Peninsula of Mexico and planted in three provenance/progeny trials in the state of Quintana Roo, Mexico, in order to characterize genetic variation in growth traits and for Hypsipyla resistance or recovery, and to assess the potential for genetic gain. Differentiation among provenances was found only for relative height growth rate (RHGR). The total years of apical attack by Hypsipyla grandella varied by a magnitude of 100% among families but showed little heritability. After 4 years, mean height per family ranged from 328 to 564 cm, 160 to 381 cm, and 253 to 390 cm at each site. Although heritabilities for height were too low for cross-site selection, sufficient heritability (View the MathML source), additive genetic coefficients of variation (AGCV = 22%), and type B genetic correlations (rb(f) = 0.74) for RHGR across the two sites with poorer growth indicated that this trait might be used as a surrogate. This would yield an estimated gain of about 17% for the best 15% of trees. At the site with better growth, there was sufficient heritability (View the MathML source) and AGCV (20%) for height at year 5 to obtain an estimated gain of 15% for the best 15% of trees. We suggest a selection strategy using the best germplasm from the best performing trial to exploit the resources on high quality sites, and the best material from the poorer sites for lower quality areas.
Seeing the trees as well as the forest: The importance of managing forest genetic resources
Forest Ecology and Management, 2014
Reliable data on the status and trends of forest genetic resources are essential for their sustainable management. The reviews presented in this special edition of Forest Ecology and Management on forest genetic resources complement the first ever synthesis of the State of the World's Forest Genetic Resources (SOW-FGR) that has just been published by the Food and Agriculture Organization. In this editorial, we present some of the key findings of the SOW-FGR and introduce the seven reviews presented in this special edition on: (1) tree genetic resources and livelihoods; (2) the benefits and dangers of international germplasm transfers; (3) genetic indicators for monitoring threats to populations and the effectiveness of ameliorative actions; (4) the genetic impacts of timber management practices; (5) genetic considerations in forest ecosystem restoration projects using native trees; (6) genetic-level responses to climate change; and (7) ex situ conservation approaches and their integration with in situ methods. Recommendations for action arising from the SOW-FGR, which are captured in the first Global Plan of Action for the Conservation, Sustainable Use and Development of Forest Genetic Resources, and the above articles are discussed. These include: increasing the awareness of the importance of and threats to forest genetic resources and the mainstreaming of genetic considerations into forest management and restoration; establishing common garden provenance trials to support restoration and climate change initiatives that extend to currently little-researched tree species; streamlining processes for germplasm exchange internationally for research and development; and the intelligent use of modern molecular marker methods as genetic indicators in management and for improvement purposes.
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.
What is mahogany? The importance of a taxonomic framework for conservation
1996
Taxonomy is an integral part of conservation and management because it allows managers to define taxa that can be managed to conserve the range of diversity in an ecosystem. This however, depends upon that classifcation being an accurate description of the taxon, and its interspecific relationships. Misidentification, or an inaccurate, or inadequate classification may lead to the loss of diversity through inadequate protection. S & h k is a genus of the Meliaceae comprising three species: S. humilis, S. macrop/ylla and S. mahagoni. The biological boundaries between these species are not clear-cut, and many biological processes within and among these taxa are poorly understood. The following areas are identified as research priorities to resolve the relationships among the three species of S&hia: hybrid zones, cytology and distribution of morphological variation. Preliminary data testing S. naacrop/pdh for DNA markers that allow identification independent of phenotype are presented here. This is the first reported analysis of cpDNA in the genus Swietenia. It is shown that while there is substantial genetic variation in the genome as a whole, variation in the chloroplast genome is low.
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.