Spatial genetic structure within size classes of the endangered tropical tree Guaiacum sanctum (Zygophyllaceae)

Abstract

Premise of the study: Patterns of spatial genetic structure (SGS) were analyzed within a population of the endangered tropical tree Guaiacum sanctum located in northwestern Costa Rica. Documentation of these patterns provides insights into the gene dispersal mechanisms that play a central role in the maintenance and structure of genetic diversity within plant populations. • Methods: Allozyme analyses were used to examine SGS in Palo Verde National Park, Costa Rica. The SGS was compared among three plots and different age classes. • Key results: High levels of genetic diversity were found overall with a pooled genetic diversity of He = 0.302 ( ± 0.02). Selfi ng was proposed as the proximate cause for signifi cant levels of heterozygote defi ciency observed across size classes and plots. An unexpected lack of SGS ( rj < 0.02) was observed for all size classes, suggesting the mixing of seeds from several adults. A parent-pair parentage analysis indicated that at least 48% of the smaller individuals within a plot were produced by parents located at distances of at least 150 m. • Conclusions: Populations of G. sanctum are established and maintained by bird-mediated, moderate- to long-distance seed dispersal, which results in a mixture of seeds from unrelated maternal individuals, effectively eliminating SGS. Proximity between individuals is, therefore, a poor predictor of family structure in this species. Long-distance seed dispersal, coupled with estimates of high genetic diversity, suggests that this endangered species has the potential for natural regeneration and restoration given the availability of suitable habitats.