Fine-scale genetic structure and gene flow within Costa Rican populations of mahogany (Swietenia macrophylla)

Abstract

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.

Optimal sampling strategy for estimation of spatial genetic structure in tree populations

“…For both AFLP and microsatellite markers in S. macrophylla, 40.9 correlation is achieved with fewer markers than used in the published analyses ( Figure 6; Lemes et al, 2003;Lowe et al, 2003). In the case of the AFLP study, 40.9 correlation with the final data set is achieved with 75 markers.…”

“…Natural forests that come under management for production, sustainable or otherwise, are likely to experience considerable disruption of SGS (Young and Merriam, 1994;Degen et al, 2001a;Lowe et al, 2003). It should be a key aim for management plans to tailor extraction such that this disturbance is minimised and that remnant genetic structure is sufficient to promote regeneration and maintenance of genetic diversity .…”

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

“…The presence of a heterozygote deficiency at every locus, coupled with the fact that very few individuals failed to amplify (these may indicate null/null homozygotes), indicates that null alleles are unlikely to explain the heterozygote deficit. We also consider a Wahlund effect to be unlikely since trees within a population tend to flower simultaneously (Lowe et al 2003). Thus, inbreeding would appear to represent the most likely explanation for the excess of homozygous alleles in the Mesoamerican populations of mahogany.…”

“…However, comparative data on allele identities and genotypes for the two mahogany species are required to test this possibility. In addition, Lowe et al (2003) suggest that environmental variation, such as differences in habitat moisture, may increase genetic differentiation, and Santa Rosa is in a drier area than the other populations. It is important to note that while microsatellites have been successfully used to reconstruct phylogenies between populations or closely related species, microsatellite-based distance measures are strongly affected by bottlenecks and fluctuations in population size (Richard & Thorpe 2001) and therefore must be treated cautiously.…”

Genetic Consequences of Multigenerational and Landscape Colonisation Bottlenecks for a Neotropical Forest Pioneer Tree, Vochysia ferruginea

“…Most tropical forest canopy trees occur at low density in old growth forest and so long distance seed and/or pollen dispersal are expected Ward et al, 2005;Hardesty et al 2005). As a result, they often show little population genetic structure (Dutech et al, 2002;Latouche-Hallé et al, 2003;Lowe et al, 2003;Ward et al, 2005;Hardesty et al, 2006). However, unlike the majority of tropical canopy trees, pioneer species often occur at locally high densities because of their light-demanding, gap-colonising strategy.…”