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The large distributional areas and ecological niches of many lichenized fungi may in part be due to the plasticity in interactions between the fungus (mycobiont) and its algal or cyanobacterial partners (photobionts). On the one hand, broad‐scale phylogenetic analyses show that partner compatibility in lichens is rather constrained and shaped by reciprocal selection pressures and codiversification independent of ecological drivers. On the other hand, sub‐species‐level associations among lichen symbionts appear to be environmentally structured rather than phylogenetically constrained. In particular, switching between photobiont ecotypes with distinct environmental preferences has been hypothesized as an adaptive strategy for lichen‐forming fungi to broaden their ecological niche. The extent and direction of photobiont‐mediated range expansions in lichens, however, have not been examined comprehensively at a broad geographic scale. Here we investigate the population genetic structure of Lasallia pustulata symbionts at sub‐species‐level resolution across the mycobiont's Europe‐wide range, using fungal MCM7 and algal ITS rDNA sequence markers. We show that variance in occurrence probabilities in the geographic distribution of genetic diversity in mycobiont‐photobiont interactions is closely related to changes in climatic niches. Quantification of niche extent and overlap based on species distribution modeling and construction of Hutchinsonian climatic hypervolumes revealed that combinations of fungal–algal interactions change at the sub‐species level along latitudinal temperature gradients and in Mediterranean climate zones. Our study provides evidence for symbiont‐mediated niche expansion in lichens. We discuss our results in the light of symbiont polymorphism and partner switching as potential mechanisms of environmental adaptation and niche evolution in mutualisms. [ABSTRACT FROM AUTHOR]

Highlights: [•] The lichen-forming fungus Lasallia pustulata is associated with multiple species of Trebouxia. [•] One of the putative Trebouxia species is exclusively found in L. pustulata. [•] Coalescent multilocus methods are a promising tool to address species boundaries in the genus Trebouxia. [ABSTRACT FROM AUTHOR]

Abstract: To facilitate marker selection in sequence-based studies on genetic diversity and symbiont selectivity in lichens we conducted a comparison of eight molecular markers in the lichen-forming fungus Lasallia pustulata and its trebouxioid photobiont. We compared mtSSU rDNA, mtLSU rDNA, MCM7, TSR1 (mycobiont) and nrITS rDNA, COX2, psbJ-L intergenic spacer, rbcL (photobiont) of 45 individuals from European populations of L. pustulata. Mycobiont and photobiont loci had congruent phylogenetic signals. Based on the results of this study we recommend the use of MCM7 and TSR1 (mycobiont), and nrITS rDNA and COX2 (photobiont). In this specific study system we found no sequence variability in the mycobiont loci EF1, nrITS rDNA, RPB1, and RPB2, which we sequenced for a subset of individuals. We had limited success amplifying GPD (mycobiont), actin and chloroplast LSU rDNA (photobiont), however, we do not rule out that these loci could be valuable markers in other species. [Copyright &y& Elsevier]

The lichen-forming genus Pertusaria under its current circumscription is polyphyletic and its phylogenetic ailiations are uncertain. Here we study the species of the genera Pertusaria and Varicellaria which contain lecanoric acid as major constituent, have disciform apothecia, strongly amyloid asci, non-amyloid hymenial gel, 1-2-spored asci, and 1- or 2-celled ascospores with thick, 1-layered walls. We infer phylogenetic relationships using maximum likelihood and Bayesian analyses based on four molecular loci (mtSSU, nuLSU rDNA, and the protein-coding, nuclear RPB1 and MCM7 genes). Our results show that the lecanoric acid-containing species form a well-supported, monophyletic group, which is only distantly related to Pertusaria s.str. he phylogenetic position of this clade is unclear, but placement in Pertusaria s.str. is rejected using alternative hypothesis testing. he circumscription of the genus Varicellaria is enlarged to also include species with non-septate ascospores. Seven species are accepted in the genus: Varicellaria culbersonii (Vezda) Schmitt & Lumbsch, comb. nov., V. hemisphaerica (Flörke) Schmitt & Lumbsch, comb. nov., V. kasandjeii (Szatala) Schmitt & Lumbsch, comb. nov., V. lactea (L.) Schmitt & Lumbsch, comb. nov., V. philippina (Vain.) Schmitt & Lumbsch, comb. nov., V. rhodocarpa (Körb.) h. Fr., and V. velata (Turner) Schmitt & Lumbsch, comb. nov. A key to the species of Varicellaria is provided. [ABSTRACT FROM AUTHOR]