Significant spatial aggregation and fine-scale genetic structure inthe homosporous fern Cyrtomium falcatum (Dryopteridaceae)

摘要

Spores of homosporous ferns are small, wind-borne and thus have the potential for longdistancedispersal. This common perception has led to a prediction of near-random spatialgenetic structure within fern populations. Spore dispersal and spore bank studies, however,indicate that most spores fall close to the maternal plant (< 5 m), supporting a prediction ofsignificant fine-scale genetic structure (FSGS) within populations. To determine which of these two hypotheses is more likely to occur in nature, we measuredinbreeding and quantified the spatial distribution of individuals and allozyme-based genotypesusing spatial autocorrelation methods within four populations of the fern Cyrtomiumfalcatum in southern South Korea. Inbreeding levels were low, and all populations exhibited significant aggregation of individualsand strong FSGS. The present results support the second hypothesis, and the substantial FSGS in C. falcatumcould reflect the unique features of most homosporous ferns (outcrossing mating systems thatlead a majority of spores to occur at short distances and a very limited dispersal distance ofmale gametes). Although fern spores are physically analogous to orchid seeds, the intensity ofFSGS exhibited in C. falcatum is four times stronger than that in 16 terrestrial orchid species.