Genetic diversity and population history of the Killarney fern, Vandenboschia speciosa (Hymenophyllaceae), at its southern distribution limit in continental Europe

Abstract

The improvement of the conservation and management strategies of endangered species requires an understanding of the history and current state of their populations and thus population genetic studies become essential. This situation is especially critical for the relict populations at the low-latitude limit of the species range, which have persisted at suitable sites across Tertiary and Quaternary climatic changes and are expected to have retained a high proportion of the genetic diversity of the species. Here we investigate the genetic diversity and structure of Vandenboschia speciosa, a vulnerable endemic European-Macaronesian species with a disjunct distribution, at its southernmost distribution limit in continental Europe (S Iberian Peninsula: Andalusia, Spain). We analysed six sporophyte populations from the eight known populations using ten microsatellite loci. The results indicated moderate genetic diversity at the regional scale but low diversity at the population level and a significant genetic differentiation between populations. Coalescent analyses revealed a population history in Andalusia characterized by a migration-drift equilibrium with historical dispersals as the main factors influencing population structure, but now predominately influenced by genetic drift, according to the genetic differentiation detected. Spatial autocorrelation and genetic-structure analyses (multivariate and STRUCTURE analyses) suggest that historic gene flow was mainly over short distances, since significant genetic relationships were detected between pairs of nearby populations (< 7 km). Only one population, the most diverse, shows evidence of long-distance dispersal. This study provides a baseline for designing appropriate conservation strategies for V. speciosa in Andalusia, where the regional government has recently approved a recovery and conservation plan.