Genetic diversity of the tropical tree Terminalia amazonia (Combretaceae) in naturally fragmented populations

The effect of long-term fragmentation on the genetic diversity of populations of the neotropical tree species, Terminalia amazonia, was studied using random amplified polymorphic DNA (RAPD) analysis. Leaf material from 104 trees was collected from three naturally fragmented gallery forest patches and three plots in nearby continuous forest in the Mountain Pine Ridge, Belize. In total, 30 RAPD bands generated by five decamer primers were used to compare the genetic diversity of the six populations in the two groups. Genetic variation within the populations (H-0), as estimated by the Shannon diversity index, ranged from 0.32 to 0.38, with an overall diversity of 0.38 (H-species). Analysis of molecular variation revealed that most (94.4%, P<0.001) of the variation was attributable to differences among individuals within populations. Population differentiation was significantly ( P = 0.038) lower among the fragmented populations than among continuous forest populations. On average, the fragmented populations also had slightly, but statistically significant ( P = 0.046) lower levels of genetic diversity. However, one gallery forest site had a higher level of genetic diversity than two of the continuous forest sites. We suggest that the long-term effect of fragmentation on the genetic diversity of tropical trees will depend upon the amount of local forest cover in proximity to the fragmented populations.