Strong genetic differentiation among populations of Fosterella rusbyi (Bromeliaceae) in Bolivia

Abstract The terrestrial bromeliad Fosterella rusbyi is endemic to the Bolivian Andes, where it mainly grows on steep, exposed slopes along roadsides and riverbeds in the seasonally dry tropical forest (SDTF) and the mesic montane forest (Yungas) biomes. We hypothesize that allopatric speciation may have been a main driver of diversification in Fosterella since the Miocene and that the scattered distribution of suitable habitats fostered the evolution of the high degree of endemism observed today. To provide further information relating to this hypothesis, we analysed the partition of genetic diversity and the extent of gene flow among natural populations of F. rusbyi using plastid and nuclear microsatellite markers. Nineteen plastid haplotypes were found, but the mean haplotype diversity per population was low. Nuclear microsatellite markers revealed 177 different multilocus genotypes (MLGs), of which 31 occurred in more than one plant. Recurrent MLGs were found in 76 plants that were therefore identified as clones. A considerable deficit of heterozygotes was detected at all nuclear loci. Geographical and genetic distances between populations were only weakly correlated with each other. Genetic divergence between populations was extremely high for both marker classes, suggesting that seed and pollen flow are low, even over short distances. The observed patterns are consistent with our hypothesis that newly available sites are sporadically colonized by one or a few founders, followed by in situ population expansion via vegetative propagation, self-pollination and/or biparental inbreeding, genetic differentiation among persistent populations and, ultimately, allopatric speciation.