Genetic diversity and mating system in a fragmented population of the Andean oak Quercus humboldtii Bonpl. (Fagaceae) (Colombia)

This study was conducted in fragmented forest populations of the Andean oak (Q. humboldtii, Fagaceae) in Colombia, where former extensive populations now occur as scattered fragments in human-dominated landscapes. Using four microsatellite loci as genetic markers, three main questions were addressed: (1) What are the effects of forest fragmentation on the genetic structure of these populations? (2) Are changes in the mating system (i.e., selfing rate, biparental inbreeding, and effective number of pollen donors) the mechanisms through which fragmentation are affecting oak populations? (3) Is pollen-mediated gene flow limited by fragmentation?; To answer these questions, an oak population in northeastern Colombia was selected and trees were sampled in a large tract of forest (ca. 4,000 ha) and in an adjacent fragmented landscape separated ca. 11 km.; Global results for genetic diversity indicate that Q. humboldtii exhibits similar levels of diversity as other temperate oak species. Fragmentation on this population seems to have decreased the observed heterozygosity of the trees in the fragmented landscape, due possibly to an increase of inbreeding. Also, significant allele reduction was observed in the seedlings from the fragmented landscape, which exhibited fewer alleles than did the adults in either landscape.; The mating system analysis indicates that the trees in the fragmented landscape are subject to significant levels of selfing in the range of 3% to 9%. Also, that mating among relatives (biparental inbreeding) is significant, and is more extreme in the smaller fragments. The strongest effect of fragmentation seems to be in the smaller number of effective genetic pollen donors ( N_ep = 1.3) that indicates that during the sampling period that consisted of non-masting years, pollen production was concentrated on few individuals. This result, coupled with significant selfing, would explain the allele impoverishment in the seedling cohort of the fragmented landscape.; Pollen gene flow was estimated using a modified paternity exclusion analysis that allows simultaneous identification of pollen flow and selfing. Pollen-mediated gene flow analysis indicates that the fragments analyzed are receiving an average of 32% of external pollen, showing no evidence of pollen isolation in this fragmented landscape. (Abstract shortened by UMI.)...