Genetic Variation and Differentiation among Five Populations of the Guanacaste Tree (Enterolobium cyclocarpum Jacq.) in Coasta Rica

In this study, we examined genetic variation and levels of differentiation between five Costa Rican populations of the Guanacaste tree (Enterolobium cyclocarpum Jacq.), using electrophoretic allozyme methods. Eleven out of 17 loci were polymorphic (P = 64.7) and five were studied in detail. For these five polymorphic loci, the observed heterozygosity ranged from 0.355 to 0.381, while the expected heterozygosity ranged from 0.340 to 0.379. Mean expected heterozygosity using these five polymorphic loci and six monomorphic loci was 0.167. All populations are near Hardy-Weinberg proportions. Only the isocitrate dehydrogenase (IDH) locus failed to conform with the Hardy-Weinberg equilibrium at one location, namely, Ciudad Colon (P-value 0.006). Genetic differentiation between populations is low, as shown by the heterogeneity of gene frequencies and the mean $G_{st}(0.039)$, even when one geographically isolated population is included in these comparisons. These findings are discussed in the light of ecological...