GENETIC-VARIATION, GENETIC-STRUCTURE AND EFFECTIVE POPULATION-SIZE INTHE TROPICAL HOLOPARASITIC ENDOPHYTE BDALLOPHYTON BAMBUSARUM (RAFFLESIACEAE)

The genetic population structure in Bdallophyton bambusarum, an endopa rasite, was studied in ten subpopulations from a subdeciduous tropical forest in Veracruz Mexico. The sample was analyzed using seven polymo rphic loci in cellulose acetate electrophoresis. Isozyme data indicate d that the subpopulations of B. bambusarum contained high genetic vari ability (H-ep = 0.452 +/- 0.045, S.E.). Our analysis suggests that alm ost each inflorescence of B. bambusarum is an individual. The subpopul ations studied were genetically similar (average Nei's genetic identit y 0.941+/-0.051 and F-ST values 0.097 +/- 0.026), suggesting that gene tic differentiation among subpopulations was small. Direct estimates o f effective population size was derived from observations of three flu orescent dyes, and from the genetic neighborhood area derived from the se data. The neighborhood area, multiplied by the total density of ind ividuals, gave an N-e = 124.84 plants, and when corrected to consider the proportion of males and females gave an N-e=118.59 individuals. An indirect estimate of Nm was obtained from the F-ST values (mean Nm=2. 037), giving an indirect estimate of the effective population size N-b = 12.8 individuals. Both values are relatively high when compared to other plant studies. The gene flow and/or effective populations size o f the studied subpopulations of B. bambusarum are believed to be large enough to prevent differentiation among subpopulations due to genetic drift.