Globally rare oceanic-montane liverworts with disjunct distributions: evidence for long-distance dispersal

Disjunct distributions in bryophytes are well known, but when it comes to the mechanisms that have shaped these distributions, especially for apparently sterile species, the historical processes leading to inter-continental disjunctions remain enigmatic. In this study, we developed microsatellite markers to investigate the spatial distribution and extent of genotypic diversity of 147 Anastrophyllum alpinum samples collected from three populations each in Nepal and Scotland (UK). For a more general insight into genetic differences, sequence divergence in A. alpinum and eight other globally rare and disjunct oceanic-montane liverworts was also assessed. A nested allele distribution of Scottish populations of A. alpinum within the allele range of the Nepalese populations, and lower levels of genetic diversity within Scottish samples indicate that the Scottish populations likely have their origins in the Sino-Himalaya. The evidence for long-distance dispersal was supported by a lack of sequence divergence in chloroplast DNA between Scottish and Nepalese populations, with only a single substitution detected from 5160 bp of plastid sequence. Low levels of sequence divergence were also detected in species with similar distributions. While Scottish populations of A. alpinum do not appear to produce spores, they do still harbour a considerable genetic diversity. This indicates that sexual reproduction has been important at some point in their history. However, the current absence of evidence for sexual reproduction needs to be taken into account when designing conservation actions for these montane species, to ensure population maintenance and ability to track suitable climate and habitat space.