Sphagnum fuscum: a glacial relict in the Pyrenees

Abstract

Climatic fluctuations during the Pleistocene shaped the current disjunct distributions of many cold-adapted species. Southern European mountains, like the Pyrenees, became climatic refugia for arctic-alpine species. These rear-edge populations are crucial for conservation because they usually harbour unique lineages. Here we studied the genetic structure and distribution of the peat moss Sphagnum fuscum (Schimp.) Klinggr. on its rear-edge in the Pyrenees to assess its regional conservation status. In total, 109 shoots from seven populations were sampled and genotyped through 16 microsatellite loci. Results showed that genetic diversity within populations is extremely poor but unique, with one to three private genotypes per population (10 genotypes in total). Populations were clearly structured (AMOVA, 81% of variation was among populations). Bayesian clustering analysis did not show groups among genotypes and populations (best K = 9, by Evanno’s ΔK) and Mantel tests indicated that there is no isolation-by-distance among populations. Thus, we suggest that S. fuscum is a glacial relict, and its current demographic and genetic structure is explained by a contraction and altitudinal migration upwards after the Local Last Glacial Maximum (LLGM) that gave place to independent founder events. We think that its rarity in the Pyrenees is due to its highly specialized ecological niche as it is a late-successional species. Remarkably, our findings point that S. fuscum might be monoecious in the Pyrenees, which enables sporophyte production and long-distance dispersal in such small and monoclonal populations. According to the IUCN criteria, the species deserves the status of Endangered (B1ab(iii)+2ab(iii); D). In addition, we suggest some conservation advice taking advantage of the genetic knowledge generated.