Photobiont associations in co-occurring umbilicate lichens with contrasting modes of reproduction in coastal Norway

Abstract

AbstractThe identity and phylogenetic placement of photobionts associated with two lichen-forming fungi,Umbilicaria spodochroaandLasallia pustulatawere examined. These lichens commonly grow together in high abundance on coastal cliffs in Norway, Sweden and Finland. The mycobiont ofU. spodochroareproduces sexually through ascospores, and must find a suitable algal partner in the environment to re-establish the lichen symbiosis.Lasallia pustulatareproduces mainly vegetatively using symbiotic propagules (isidia) containing both symbiotic partners (photobiont and mycobiont). Based on DNA sequences of the internal transcribed spacer region (ITS) we detected seven haplotypes of the green-algal genusTrebouxiain 19 pairs of adjacent thalli ofU. spodochroaandL. pustulatafrom five coastal localities in Norway. As expected,U. spodochroaassociated with a higher diversity of photobionts (seven haplotypes) than the mostly asexually reproducingL. pustulata(four haplotypes). The latter was associated with the same haplotype in 15 of the 19 thalli sampled. Nine of the lichen pairs examined share the same algal haplotype, supporting the hypothesis that the mycobiont ofU. spodochroamight associate with the photobiont ‘pirated’ from the abundant isidia produced byL. pustulatathat are often scattered on the cliff surfaces. Up to six haplotypes ofTrebouxiawere found within a single sampling site, indicating a low level of specificity of both mycobionts for their algal partner. Most photobiont strains associated with species ofUmbilicariaandLasallia, including samples from this study, represent phylogenetically closely related taxa ofTrebouxiagrouped within a small number of main clades (Trebouxiasp.,T. simplex/T. jamesii, andT. incrustata+T. gigantea). Three of the photobiont haplotypes were found only inU. spodochroathalli.