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

Abstract

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.

Patterns of genetic variation in Pinus chiapensis, a threatened Mexican pine, detected by RAPD and mitochondrial DNA RFLP markers

“…The estimate of ⌽ ST derived here for P. chiapensis (0.226) is substantially higher than values derived for other tree species using similar methods (Isabel et al, 1995;Allnutt et al, 1999Allnutt et al, , 2001Gillies et al, 1999;Bekessy et al, 2002). This value is also high compared to values for other pine species using a variety of different markers.…”

“…The AMOVA programme generates ⌽ statistics (Excoffier et al, 1992), which are analogous to Wright's F ST (Wright, 1951). This approach has been widely adopted in the analysis of RAPD data (eg, Gillies et al, 1997Gillies et al, , 1999Allnutt et al, 1999;Nybom and Bartish, 2000;Ehtisham-ul-Haq et al, 2001;Bekessy et al, 2002), allowing comparison of results with a variety of other studies.…”

Genetic diversity of the tropical tree Terminalia amazonia (Combretaceae) in naturally fragmented populations

“…Bands were numbered in order of increasing primer number and fragment size (Table 2). (Gillies et al, 1999), 0.45 for Cedrela odorata (Gillies et al, 1997), and 0.59 for Poulsenia armata (Aide and Rivera, 1998). Care should be taken when comparing values across studies because they are influenced by the genetic markers employed and because of inconsistent methods of calculating diversity (eg, Gillies et al, 1999;Martin and Bermejo, 2000).…”

“…For example, a study in Costa Rica found that more than 96% of the genetic variation in Dendropanax arboreus, Inga thibaudiana, and Protium glabrum was attributable to differences within plots along a 9 km transect (Schierenbeck et al, 1997). However, population differentiation does tend to rise with increasing distances between populations and may be exacerbated by forest fragmentation (Hall et al, 1996;Aide and Rivera, 1998;Gillies et al, 1999).…”

Genetic structure of Mesoamerican populations of Big‐leaf mahogany (Swietenia macrophylla) inferred from microsatellite analysis

“…While evidence is lacking for decreased genetic variation among human-impacted populations of Swietenia spp. (Gillies et al 1999;White et al 1999), the record of logging in Mexico may be sufficiently long relative to the mahogany life cycle to register discernible population genetic change in harvested forests.…”