Population structure and mating system in Tachigali versicolor, a monocarpic neotropical tree

Patterns of genetic differentiation among six populations of Tachigali versicolor (Fabaceae: Papilionoideae) on Barro Colorado Island, Panama were investigated. Average gene diversity within any one population (H_e) was 0.073 (SD 0.010), and He over all populations was 0.080. Populations showed relatively little genetic differentiation (mean G_ST=0.069), suggesting high levels of gene flow. A direct estimate of pollen flow indicated that 21% of the pollen received by a cluster of five trees had travelled at least 500 m.

Genetic analyses of the mating system showed complete outcrossing (t_m=0.998, SE±0.054; mean t_s=1.001, SE±0.063). Estimates of F at different life stages showed a slight deficiency of heterozygotes in the six population samples, a slight excess among the 25 flowering adult trees, and no significant deviation in heterozygosity in progeny arrays. These differences may reflect the monocarpic life history of T. versicolor, in which adults flowering in a given year represent a temporal genetic bottleneck, producing a Wahlund effect in genotype frequencies in the overall population. This interpretation of genetic structure in T. versicolor suggests the overriding importance of ecological factors and life history on genetic processes in natural populations.