Genetic diversity in Mesoamerican populations of mahogany (Swietenia macrophylla), assessed using RAPDs

Swietenia macrophylla King, a timber species native to tropical America, is threatened by selective logging and deforestation. To quantify genetic div ersity within the species and monitor the impact of selective logging, popu lations were sampled across Mesoamerica, from Mexico to Panama, and analyse d for RAPD DNA variation. Ten decamer primers generated 102 polymorphic RAP D bands and pairwise distances were calculated between populations accordin g to Nei, then used to construct a radial neighbour-joining dendrogram and examine intra- and interpopulation variance coefficients, by analysis of mo lecular variation (AMOVA). Populations fi om Mexico clustered closely toget her in the dendrogram and were distinct from the rest of the populations. T hose from Belize also clustered closely together. Populations from Panama, Guatemala, Costa Rica, Nicaragua and Honduras, however, did not cluster clo sely by country but were more widely scattered throughout the dendrogram. T his result was also reflected by an autocorrelation analysis of genetic and geographical distance. Genetic diversity estimates indicated that 80% of d etected variation was maintained within populations and regression analysis demonstrated that logging significantly decreased population diversity (P= 0.034). This study represents one of the most wide-ranging surveys of molec ular variation within a tropical tree species to date. It offers practical information for the future conservation of mahogany and highlights some fac tors that may have influenced the partitioning of genetic diversity in this species across Mesoamerica.