High genetic diversity and moderate genetic structure in the self-incompatible, clonal Bromelia hieronymi (Bromeliaceae)

Abstract

Genetic diversity and population structure in plants are directly associated with the reproductive system and gene flow by pollen and seeds. We examined the reproductive system, pollination biology, genetic diversity and structure, and gene flow in Bromelia hieronymi, an endemic species of the humid Brazilian chaco. We characterized the reproductive system by hand-pollination experiments and the pollination biology by observations, both in situ. For the genetic analysis we used nuclear and plastid microsatellite markers. Bromelia hieronymi is allogamous, self-incompatible and clonal. The potential pollinators were hawkmoths and hummingbirds, but butterflies were also observed. The three populations studied showed high levels of genetic diversity for nuclear (mean observed and expected heterozygosity HO = 0.624 and HE = 0.558) and plastid markers (mean HE = 0.688) and moderate genetic structure (fixation index FST = 0.138); we found evidence of genetic bottlenecks in two populations. The self-incompatibility system may have a strong relationship with gene flow, and its association with clonality may be responsible for the high genetic diversity observed. Gene flow by seeds was more efficient than gene flow by pollen. These results show that B. hieronymi responds negatively to reduction in population size. Therefore, continuous conservation strategies are necessary to avoid increasing genetic differentiation in the species, maintaining its evolutionary potential for adaptation.