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

Abstract

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.

Circuit theory predicts gene flow in plant and animal populations

“…Both are vulnerable to extinction because of habitat loss and overexploitation (21), and conservation efforts rely on our ability to identify important landscape connections and barriers. The plant data set consisted of eight Central American populations of big-leaf mahogany (Swietenia macrophylla), an insect-pollinated tropical tree, with 287 individuals typed at seven microsatellite loci by Novick et al (22) (Fig. 1A).…”

“…Both of the original studies had found residual variation unexplained by distance and had attributed that variation to migration barriers or other factors driving differentiation within each species' range. For example, Novick et al (22) noted that the southernmost mahogany population [Tonosí (Fig. 1 A)] appeared to be more differentiated from other populations than would be expected from distance alone, and speculated that the increased differentiation may result from geographic barriers and/or historical events.…”

“…For big-leaf mahogany, existing range maps differ markedly from one another (26,27) and may not adequately capture the species' long-term regional distribution because mahogany is long-lived and likely experienced range expansions during glacial periods (22). Currently, the species is widespread throughout Central America, occurring in every country and in every Mexican state from the Isthmus of Tehuantepec through Panama (26,27,32).…”

Genetic structure and genetic diversity of <em>Swietenia macrophylla</em> in areas subjected to selective logging in Quintana Roo, Mexico

“…All the results involving allelic and genotypic information indicate that Mexican populations could maintain overall low levels of genetic diversity and high scores for the coeffi cient of fi xation by historic reasons. This is because there is evidence that suggests that northern populations of Swietenia macrophylla maintain lower heterozygosity due to the colonization toward northern latitudes from South America , Novick et al, 2003, a pattern that is still observed along the distribution of this species in Mexico (Alcalá et al, 2014). Statistically signifi cant differences between adults and saplings were detected for the number of alleles present at different frequency categories.…”

“…At this rate, population reductions should occur at a very high magnitude to produce marked reductions, as the loss of rare alleles (those that are lost fi rst) shows a limited effect on this parameter in the short-term (Hedrick, 2000). However, the absence of differences in heterozygosity between adults and saplings may be explained by the overall low levels of genetic diversity that Mexican populations sustain as a result of the expansion of its geographic range, as explained above , Novick et al, 2003Alcalá et al, 2014).…”