GENETIC-VARIATION AND DIFFERENTIATION AMONG 5 POPULATIONS OF THE GUANACASTE TREE (ENTEROLOBIUM-CYCLOCARPUM JACQ) IN COSTA-RICA

In this study, we examined genetic variation and levels of differentia tion between five Costa Rican populations of the Guanacaste tree (Ente rolabium cyclocarpum Jacq.), using electrophoretic allozyme methods. E leven out of 17 loci were polymorphic (P = 64.7) and five were studied in detail. For these five polymorphic loci, the observed heterozygosi ty ranged from 0.355 to 0.381, while the expected heterozygosity range d from 0.340 to 0.379. Mean expected heterozygosity using these five p olymorphic loci and six monomorphic loci was 0.167. All populations ar e near Hardy Weinberg proportions. Only the isocitrate dehydrogenase ( IDH) locus failed to conform with the Hardy-Weinberg equilibrium at on e location, namely, Ciudad Colon (P-value 0.006). Genetic differentiat ion between populations is low, as shown by the heterogeneity of gene frequencies and the mean G(st) (0.039), even when one geographically i solated population is included in these comparisons. These findings ar e discussed in the light of ecological and historical considerations.