Format: ORAL

Joan Cusc-Borrs1,2,3, Nria Garcia-Jacas2, Eullia Pladevall-Izard1, Jordi Lpez-Pujol2, Nil Escol-Lamora1, Aaron Prez-Haase1.

1 Universitat de Barcelona, Barcelona, Spain. 2 Institut Botànic de Barcelona (IBB, CSIC-ICUB), Barcelona, Spain. 3 Universidad de Sevilla, Sevilla, Spain.

Rear edge populations match in many cases with the extreme of species niche. During the Holocene, one strategy for cold-adapted species has been migrating to refugia while conserving their ecological niche, in what is known as trailing edges. In such populations, long-distance dispersal is thus a crucial trait that may be under selective pressure. In the genus Sphagnum L. (peat mosses) such function relies on spores. Its production may be compromised by the species mating system, with sporophytes being less frequent in dioicous species rather than monoicous. Here, we studied the genetic structure and demographic traits of Sphagnum fuscum (Schimp.) Klinggr., a putative dioicous species, on its rear edge in the Pyrenees. We entirely genotyped seven populations through 16 microsatellite loci, and we assessed the production of sporophytes in each population. Genetic diversity within populations is extremely poor, harbouring only one to three private genotypes per population. Each genotype constitutes a separate group according to a Bayesian cluster analysis. Surprisingly, we found sporophytes in some monoclonal populations. We suggest that S. fuscum is a glacial relict in the Pyrenees. Its current genetic structure can be explained by a demographical contraction and altitudinal migration upwards after the Local Last Glacial Maximum. The remarkable uniqueness of every genotype may result from independent founder events and strong isolation. Our findings indicate that S. fuscum may have shifted to monoicy in the Pyrenees. This trait would enhance the fitness of small populations with limited and fragmented suitable habitat. Consequently, we think that S. fuscum would bea good model to study the molecular mechanisms underlying sex determination in the genus. Furthermore, it could provide valuable insights to understand mating system transitions in Sphagnum under an evolutionary ecology perspective.