Does altitude shape molecular diversity and richness of bryophytes in Madeira's natural forest? A case study with four bryophyte species at two altitudinal levels

Background and aims – The importance of altitude as a driver of both species and genetic diversity has been widely acknowledged, since it affects other environmental variables such as temperature and precipitation, also influencing the distribution of plant species and, potentially, intraspecific genetic variation. In this study, we hypothesize that molecular (haplotype) variation within four Macaronesian bryophyte species co-varies with other diversity variables for two altitudinal levels. Methods – Samples with molecular and floristic data were grouped into two altitudinal levels for mean comparisons. We measured the genetic diversity (haplotype diversity) of four bryophytes ( Exsertotheca intermedia, Isothecium prolixum, Frullania polysticta and Porella canariensis ) and determined floristic richness variables as well as each species cover using the data collected in 92 plots across the natural Laurel forest of Madeira Island. Molecular analyses included the sequencing of ITS1-5.8S-ITS2 and the chloroplast DNA rps 4- trn T- trn L region. A haplotype diversity index, based on haplotype frequencies, was also calculated and compared with the percentage of sporophytes, for each studied species. Key results – The results obtained by the mean comparisons revealed that bryophyte species richness and endemic species richness are higher for high altitudes levels in the natural forest. A coincident pattern between the species richness and the genetic diversity was observed for the mosses I. prolixum and E. intermedia, in which a higher species cover and genetic diversity occurred at high altitudes. However, F. polysticta displayed an inverse pattern, and P. canariensis did not present any significant differences in cover and haplotype frequency means. Conclusion – From a conservation and management perspective, our findings highlight the importance of maintaining large patches of Macaronesian bryophyte species, since our results indicate a possible effect of altitude on species cover, affecting species genetic diversity. This should be considered in management plans, especially for endemics and red-listed species.