Genetic diversity, genetic drift and mixed mating system in small subpopulations of Dyckia ibiramensis, a rare endemic bromeliad from Southern Brazil

摘要

Dyckia ibiramensis is a naturally rare, endemic and threatened bromeliad which occurs naturally on 4 km of rocky river outcroppings in Southern Brazil. For this study, subpopulations of the species were characterized based on size and genetics, to compile information for in situ and ex situ conservation strategies. A census of the rosettes was undertaken for each subpopulation and seven allozyme polymorphic loci were used to estimate genetic diversity and structure of adults and offspring and assess the mating system. In general, the subpopulations were small and most of the rosettes were aggregated into clumps. The species showed a high genetic diversity ([^(H)]_e = 0.219 hat{H}_{e} = 0.219 ) and significant fixation index ([^(f)] = 0.642, hat{f} = 0.642, P ≤ 0.05). The estimate of differentiation among all adult subpopulations indicate pronounced genetic structure ([^(G)]¢_ST = 0.674 hat{G}^{prime}_{ST} = 0.674 ). D. ibiramensis has a mixed mating system and multilocus outcrossing rates [^(t)]_m hat{t}_{m} were variable between subpopulations. This study demonstrates the importance of in situ preservation of all subpopulations for the maintenance of species diversity. For effective ex situ conservation, it would be necessary to collect seeds from 52 to 99 seed-rosettes, depending on the target population.