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Compared to other organisms, such as vascular plants or mosses, lichen-forming fungi have a high number of species occurring in both northern and southern hemispheres but are largely absent from intermediate, tropical latitudes. For instance, ca. 160 Antarctic species also occur in polar areas or mountainous temperate regions of the northern hemisphere. Early interpretations of this particular distribution pattern were made in terms of vicariance or long-distance dispersal. However, it was not until the emergence of phylogenetics and the possibility of dating past diversification and colonization events that these initial hypotheses started to be evaluated. The premise of a relatively recent colonization of the southern hemisphere by boreal lichens through long-distance dispersal has gained support in recent studies based on either the comparison of genetic affinities (i.e., tree topology) or more robust, statistical migratory models. Still, the scarcity of such studies and a concern that taxonomic concepts for bipolar lichens are often too broad preclude the generation of sound explanations on the mechanisms and origin of such fascinating disjunct distributions. This review provides an up-to-date overview of bipolar distributions in lichen-forming fungi and their photobionts. Evidence provided by recent, molecular-based studies as well as data on the type of lichen reproduction, dispersal ability, photobiont identity and availability, and habitat preferences are brought together to discuss how and when these distributions originated and their genetic footprints. Ideas for future prospects and research are also discussed.

Aim: The hypotheses proposed to explain the high percentage of bipolar lichens in Antarctica have never been explicitly tested. We used the strictly bipolar, coastal lichenized fungus Mastodia tessellata (Verrucariaceae, Ascomycota) and its photobionts (Prasiola, Trebouxiophyceae, Chlorophyta) as model species to discern whether this extraordinary disjunction originated from vicariance or long-distance dispersal. Location: Coasts of Antarctica, Tierra del Fuego (Chile), Alaska (USA) and British Columbia (Canada). Methods: Based on a comprehensive geographical (315 specimens and 16 populations from Antarctica, Tierra del Fuego and North America) and molecular sampling (three and four loci for the fungus and algae respectively), we implemented explicit Bayesian methods to compare alternative hypotheses of speciation and migration, and performed dating analyses for the fungal and algal partner, in order to infer the timing of the colonization events and the direction of gene flow among distant, disjunct areas. Results: Mastodia tessellata comprises two fungal species which in turn associate with three photobiont lineages along the studied distribution range. Independent estimation of divergence ages for myco- and photobionts indicated a middle to latest Miocene species split in the Southern Hemisphere, and a late Miocene to Pleistocene acquisition of the bipolar distribution. Comparison of migration models and genetic diversity patterns suggested an austral origin for the bipolar species. Main conclusions: The complex evolutionary history of Mastodia tessellata s.l. can be explained by a combination of vicariant and long-distance dispersal mechanisms. We provide novel evidence of a pre-Pleistocene long-term evolution of lichens in Antarctica as well as for bipolar distributions shaped by Southern to Northern Hemisphere migratory routes without the need for stepping stones.

The phylogenetic relationship of lecanoroid lichens is studied using two data sets: 1) a 2-locus data set including 251 OTUs representing 150 species, and 2) a 6-locus data set with 82 OTUs representing 53 species. The genus Lecanora as currently circumscribed is shown to be highly polyphyletic and several genera, including Adelolecia, Arctopeltis, Bryonora, Carbonea, Frutidella, Lecidella, Miriquidica, Palicella, Protoparmeliopsis, Pyrrhospora, and Rhizoplaca are nested within Lecanora sensu lato. A core group of Lecanora is supported as monophyletic and includes species of the L. carpinea, L. rupicola, and L. subcarnea groups, and a core group of the L. subfusca group. Three monophyletic clades that are well supported in our analyses and well characterized by phenotypical characters are accepted here: 1) Myriolecis to accommodate the Lecanora dispersa group and Arctopeltis; 2) Protoparmeliopsis for the L. muralis group; and 3) Rhizoplaca is emended to include three placodioid taxa previously classified in Lecanora (L. novomexicana. L. opiniconensis, L. phaedrophthalma), whereas R. aspidophora and R. peltata are excluded from Rhizoplaca. The latter is transferred into Protoparmeliopsis. Lecidella is strongly supported as a monophyletic group. Our studies indicate the presence of additional clades of species currently placed in Lecanora sensu lato that warrant taxonomic recognition but additional data will be necessary before the circumscription of these entities is fully understood. 37 new combinations are proposed into the genera Myriolecis (30), Protoparmeliopsis (2), and Rhizoplaca (5).

Aim The relative importance of long-distance dispersal versus vicariance in determining the distribution of lichen-forming fungi remains unresolved. Here, we examined diversity and distributions in a cosmopolitan lichen-forming fungal species complex, Rhizoplaca melanophthalma sensu lato (Ascomycota), across a broad, intercontinental geographical distribution. We sought to determine the temporal context of diversification and the impacts of past climatic fluctuations on demographic dynamics within this group. Location Antarctica, Asia, Europe, North America and South America. Methods We obtained molecular sequence data from a total of 240 specimens of R. melanophthalma s.l. collected across five continents. We assessed the monophyly of candidate species using individual gene trees and a tree from a seven-locus concatenated data set. Divergence times and relationships among candidate species were evaluated using a multilocus coalescent-based species tree approach. Speciation probabilities were estimated using the coalescent-based species delimitation program BPP. We also calculated statistics on molecular diversity and population demographics for independent lineages. Main conclusions Our analyses of R. melanophthalma s.l. collected from five continents supported the presence of six species-level lineages within this complex. Based on current sampling, two of these lineages were found to have broad intercontinental distributions, while the other four were limited to western North America. Of the six lineages, five were found on a single mountain in the western USA and the sixth occurred no more than 200 km away from this mountain. Our estimates of divergence times suggest that Pleistocene glacial cycles played an important role in species diversification within this group. At least three lineages show evidence of recent or ongoing population expansion.

Bryophyte establishment represents a positive feedback process that enhances soil development in newly exposed terrain. Further, biological nitrogen (N) fixation by cyanobacteria in association with mosses can be an important supply of N to terrestrial ecosystems, however the role of these associations during post-glacial primary succession is not yet fully understood. Here, we analyzed chronosequences in front of two receding glaciers with contrasting climatic conditions (wetter vs drier) at Cordillera Darwin (Tierra del Fuego) and found that most mosses had the capacity to support an epiphytic flora of cyanobacteria and exhibited high rates of N2 fixation. Pioneer moss-cyanobacteria associations showed the highest N2 fixation rates (4.60 and 4.96 µg N g-1 bryo. d-1) very early after glacier retreat (4 and 7 years) which may help accelerate soil development under wetter conditions. In drier climate, N2 fixation on bryophyte-cyanobacteria associations was also high (0.94 and 1.42 µg N g-1 bryo. d-1) but peaked at intermediate-aged sites (26 and 66 years). N2 fixation capacity on bryophytes was primarily driven by epiphytic cyanobacteria abundance rather than community composition. Most liverworts showed low colonization and N2 fixation rates, and mosses did not exhibit consistent differences across life forms and habitat (saxicolous vs terricolous). We also found a clear relationship between cyanobacteria genera and the stages of ecological succession, but no relationship was found with host species identity. Glacier forelands in Tierra del Fuego show fast rates of soil transformation which imply large quantities of N inputs. Our results highlight the potential contribution of bryophyte-cyanobacteria associations to N accumulation during post-glacial primary succession and further describe the factors that drive N2-fixation rates in post-glacial areas with very low N deposition.

The Antarctic Dry Valleys are unable to support higher plant and animal life and so microbial communities dominate biotic ecosystem processes. Soil communities are well characterized, but rocky surfaces have also emerged as a significant microbial habitat. Here, we identify extensive colonization of weathered granite on a landscape scale by chasmoendolithic microbial communities. A transect across north-facing and south-facing slopes plus valley floor moraines revealed 30–100 % of available substrate was colonized up to an altitude of 800 m. Communities were assessed at a multidomain level and were clearly distinct from those in surrounding soils and other rock-inhabiting cryptoendolithic and hypolithic communities. All colonized rocks were dominated by the cyanobacterial genus Leptolyngbya (Oscillatoriales), with heterotrophic bacteria, archaea, algae, and fungi also identified. Striking patterns in community distribution were evident with regard to microclimate as determined by aspect. Notably, a shift in cyanobacterial assemblages from Chroococcidiopsis-like phylotypes (Pleurocapsales) on colder–drier slopes, to Synechococcus-like phylotypes (Chroococcales) on warmer–wetter slopes. Greater relative abundance of known desiccation-tolerant bacterial taxa occurred on colder–drier slopes. Archaeal phylotypes indicated halotolerant taxa and also taxa possibly derived from nearby volcanic sources. Among the eukaryotes, the lichen photobiont Trebouxia (Chlorophyta) was ubiquitous, but known lichen-forming fungi were not recovered. Instead, fungal assemblages were dominated by ascomycetous yeasts. We conclude that chasmoendoliths likely constitute a significant geobiological phenomenon at lower elevations in granite-dominated Antarctic Dry Valley systems.

Ramalina farinacea is an epiphytic lichen-forming fungus with a broad geographic distribution, especially in the Northern Hemisphere. In the eighties of the last century, it was hypothesized that R. farinacea had originated in the Macaronesian–Mediterranean region, with the Canary Islands as its probable southernmost limit, and thereafter it would have increased its distribution area. In order to explore the phylogeography of this emblematic lichen, we analyzed 120 thalli of R. farinacea collected in 38 localities distributed in temperate and boreal Europe, the Western Mediterranean Basin, and several Macaronesian archipelagos in the Atlantic Ocean. Data from two nuclear markers (nrITS and uid70) of the mycobiont were obtained to calculate genetic diversity indices to infer the phylogenies and haplotype networks and to investigate population structure. In addition, dating analysis was conducted to provide a valuable hypothesis of the timing of the origin and diversification of R. farinacea and its close allies. Our results highlight that phylogenetic species circumscription in the “Ramalina farinacea group” is complex and suggests that incomplete lineage sorting is at the base of conflicting phylogenetic signals. The existence of a high number of haplotypes restricted to the Macaronesian region, together with the diversification of R. farinacea in the Pleistocene, suggests that this species and its closest relatives originated during relatively recent geological times and then expanded its range to higher latitudes. However, our data cannot rule out whether the species originated from the Macaronesian archipelagos exclusively or also from the Mediterranean Basin. In conclusion, the present work provides a valuable biogeographical hypothesis for disentangling the evolution of this epiphytic lichen in space and time.

Some definitions of the term ‘lichen’ have often emphasized the role of the mycobiont as exhabitant in the symbiosis. Mastodia tessellata and Turgidosculum ulvae, both forming lichen-like associations with foliose algae, have traditionally defied that definition. In this study, we delve into the poorly known association of T. ulvae with Blidingia minima. Using four molecular markers (nrLSU, nrSSU, RPB1, mtSSU) we show that T. ulvae is a member of the family Verrucariaceae, closely related to the marine species Verrucaria ditmarsica. The presence of bitunicate asci and single-cell ascospores is confirmed. Our analysis of a fragment of the rbcL marker demonstrates that the photosynthetic partner belongs to B. minima, although relationships within this taxon remain unclear. Transmission electron microscopy allowed us to illustrate how T. ulvae interacts with Blidingia cells, and how haustoria in that species differ from those previously investigated in other marine lichen-forming fungi.

The biological nature of some symbioses is unclear because it is often not easy to discern whether the symbionts obtain any benefits from the association. Mastodia tessellata, a symbiosis between a leafy green alga and a fungus of uncertain phylogenetic position, is among the most investigated, controversial, and poorly understood associations. Because it has been difficult to determine whether this association is mutually beneficial or parasitic, not all scientists accept M. tessellata as a true lichen symbiosis. Mastodia tessellata is thus an interesting model to illustrate the interactions and processes that occur in fungal—algal symbioses. To improve our understanding of this association, we address the phylogenetic positions of the bionts involved and examine their interactions at the ultrastructural level. Examining the nuLSU and nuSSU gene regions of the mycobiont and the rbcL gene region of the photobiont, we found the fungus to be related to a group of marine species in the genus Verrucaria, family Verrucariaceae, despite its present ascription to the family Mastodiaceae. In addition, the photobiont of the symbiosis emerged as closely related to the North American species Prasiola borealis. Our electron microscopy observations provide new information on the process of fungal colonization of the algal thalli, as well as on relationships between the symbionts during different stages of colonization. The special features of this lichen symbiosis are discussed and compared with other examples of fungal symbioses in nature.

We studied the evolutionary history of the Parmeliaceae (Lecanoromycetes, Ascomycota),one of the largest families of lichen-forming fungi with complex and variable morphologies,also including several lichenicolous fungi. We assembled a six-locus data set including nuclear, mitochondrial and low-copy protein-coding genes from 293 operational taxonomic units (OTUs). The lichenicolous lifestyle originated independently three times in lichenized ancestorswithin Parmeliaceae, and a new generic name is introduced for one of these fungi. In all cases,the independent origins occurredc. 24 million yr ago. Further, we show that the Paleocene,Eocene and Oligocene were key periods when diversification of major lineages within Parmeli-aceae occurred, with subsequent radiations occurring primarily during the Oligocene andMiocene. Our phylogenetic hypothesis supports the independent origin of lichenicolous fungi associ-ated with climatic shifts at the Oligocene–Miocene boundary. Moreover, diversification burstsat different times may be crucial factors driving the diversification of Parmeliaceae. Addition-ally, our study provides novel insight into evolutionary relationships in this large and diversefamily of lichen-forming ascomycetes. ancestral characterreconstruction, Ascomycota, lichenicolousfungi, mutualism, Parmeliaceae, phylogeny, Raesaenenia