Contrasting patterns of genetic variation in central and peripheral populations of dryopteris fragrans (Fragrant wood fern) and implications for colonization dynamics and conservation

摘要

Premise of research. Ferns are vital components of temperate and tropical ecosystems, but they have not been examined in the context of a central-peripheral hypothesis. Dryopteris fragrans is an ideal species to examine the genetic variation between central and peripheral populations because of its arctic north to temperate south distribution pattern. In addition to understanding colonization dynamics, our study also addresses the issue regarding the conservation value of peripheral plant populations. Methodology. We examined 82 individuals from 22 populations from northern Canada (N-CA) and the northeastern United States (NE-US), which represent central and peripheral populations of D. fragrans, respectively. Two-hundred two loci were resolved using inter-simple sequence repeat markers, allowing analyses of genetic diversity and population structure, insights into gene flow and mating system, and correlations of genetic diversity with geographical distance, population size, and air temperature. Pivotal results. Dryopteris fragrans exhibits high genetic diversity at the species level, with most of its genetic variation due to differences between populations. At the regional level, however, there is a sharp contrast in the patterns of genetic variation between N-CA and NE-US populations, with the latter exhibiting low genetic diversity, high population differentiation, low gene flow, and a predominantly inbreeding mating system. The NE-US populations also exhibit several unique loci that indicate that they are not merely a reduced representative of the overall genetic diversity of the species. Conclusions. Dryopteris fragrans in the NE-US are genetically distinct from those in N-CA, and this result may serve as justification for the species’ conservation in the NE-US. Our results also indicate that D. fragrans in the NE-US may have originated from the Canadian populations through several instances of single-spore founding events facilitated by long-distance spore dispersal and self-fertilization.