Genetic structure of a bird-dispersed tropical tree (Dendropanax arboreus) in a fragmented landscape in Mexico

We analyzed the genetic structure of the tropical tree Dendropanax arboreus (Araliaceae) in relation to habitat fragmentation. Genetic variation, structure, and genetic differentiation among populations from Los Tuxtlas tropical rainforest were estimated using ISSRs as molecular markers. DNA from 219 individuals belonging to 9 populations was amplified with 4 primers yielding a total of 75 loci. Adults and juveniles from each population were analyzed to assess the genetic diversity and structure pre and post-fragmentation, respectively. Dendropanax arboreus showed high levels of genetic diversity (h = 0.253) and significant but low genetic differentiation among populations (0 = 0.062). A hierarchical analysis of the gvenetic structure showed that 91.5% of the genetic variation is attributable to individual differences within populations. The average Nei's genetic distance among populations was low (D = 0.034) and genetic distance among pairs of populations increased with geographic distance separating them. Because genetic diversity is similar between adult and juvenile trees at all but 2 populations, we suggest that seed dispersal prevented genetic differentiation and maintains genetic connectivity among fragments and continuous forest populations. Juvenile populations showed a higher genetic differentiation (theta = 0.15) than adult trees, indicating a role of genetic drift via reduced population size.