Toby Spribille

Basidiomycete yeasts in the cortex of ascomycete macrolichens

Lichens assemble in three parts Lichen growth forms cannot be recapitulated in the laboratory by culturing the plant and fungal partners together. Spribille et al. have discovered that the classical binary view of lichens is too simple. Instead, North American beard-like lichens are constituted of not two but three symbiotic partners: an ascomycetous fungus, a photosynthetic alga, and, unexpectedly, a basidiomycetous yeast. The yeast cells form the characteristic cortex of the lichen thallus and may be important for its shape. The yeasts are ubiquitous and essential partners for most lichens and not the result of lichens being colonized or parasitized by other organisms. Science, this issue p. 488 Complete functioning lichen thalli have three partners: alga and ascomycete, plus a basidiomycete yeast. For over 140 years, lichens have been regarded as a symbiosis between a single fungus, usually an ascomycete, and a photosynthesizing partner. Other fungi have long been known to occur as occasional parasites or endophytes, but the one lichen–one fungus paradigm has seldom been questioned. Here we show that many common lichens are composed of the known ascomycete, the photosynthesizing partner, and, unexpectedly, specific basidiomycete yeasts. These yeasts are embedded in the cortex, and their abundance correlates with previously unexplained variations in phenotype. Basidiomycete lineages maintain close associations with specific lichen species over large geographical distances and have been found on six continents. The structurally important lichen cortex, long treated as a zone of differentiated ascomycete cells, appears to consistently contain two unrelated fungi.

Lichens and lichenicolous fungi of the Klondike Gold Rush National Historic Park, Alaska, in a global biodiversity context

Abstract The lichen flora of southeast Alaska has been explored for over 100 years, but remains poorly known. In the first survey of its kind from the region, we report 766 taxa of lichens and lichenicolous fungi from the Klondike Gold Rush National Historic Park. Coming from a park only 53 km2 in size, this represents one of the largest numbers of lichenized and lichenicolous fungi per unit area ever reported and the largest number ever reported from any United States National Park of any size. One lichen genus, four lichen species and one species of lichenicolous fungus are described as new to science: Steineropsis alaskana gen. et sp. nov. (Peltigerales), Coccotrema hahriae and Pertusaria mccroryae (both Pertusariales), Stereocaulon klondikense (Lecanorales) and Corticifraga scrobiculatae (Lecanoromycetes incertae sedis). The new combinations Coccotrema minutum and Nesolechia fusca are made and Parmelia elongata is reduced to synonymy under Hypogymnia duplicata. Seventy-five taxa could not be assigned a species name at this time and represent a pool of critical and/or potentially undescribed taxa. Thirty-four taxa are new or confirmed for North America, including seventeen lichen taxa, one species of saprophytic Dothideomycetes, and sixteen species of lichenicolous fungi. Five taxa of eastern North American distribution are reported for the west for the first time. A total of 196 taxa are new for Alaska. We report the presence of novel secondary chemical compounds in Bryoria, Cladonia, Hypogymnia and Pertusaria. Based on a Chao analysis of single and two-time occurrences we estimate we have captured not more than 83% of the macrolichen and 64% of the microlichen flora, with the total flora likely exceeding 1000 taxa. We provide an overview of the lichen inventories with highest species number worldwide and discuss the Klondike in the context of broader patterns in lichen richness. Global models of climate change in the coming century are unanimous in predicting greater temperature increases at higher latitudes than at low latitudes. We hope that our data will lead to a reconsideration of the potential extent of biodiversity at high latitudes.

Multilocus phylogeny of the lichen-forming fungal genus Melanohalea (Parmeliaceae, Ascomycota): Insights on diversity, distributions, and a comparison of species tree and concatenated topologies

Accurate species circumscriptions are central for many biological disciplines and have critical implications for ecological and conservation studies. An increasing body of evidence suggests that in some cases traditional morphology-based taxonomy have underestimated diversity in lichen-forming fungi. Therefore, genetic data play an increasing role for recognizing distinct lineages of lichenized fungi that it would otherwise be improbable to recognize using classical phenotypic characters. Melanohalea (Parmeliaceae, Ascomycota) is one of the most widespread and common lichen-forming genera in the northern Hemisphere. In this study, we assess traditional phenotype-based species boundaries, identify previously unrecognized species-level lineages and discuss biogeographic patterns in Melanohalea. We sampled 487 individuals worldwide, representing 18 of the 22 described Melanohalea species, and generated DNA sequence data from mitochondrial, nuclear ribosomal, and protein-coding markers. Diversity previously hidden within traditional species was identified using a genealogical concordance approach. We inferred relationships among sampled species-level lineages within Melanohalea using both concatenated phylogenetic methods and a coalescent-based multilocus species tree approach. Although lineages identified from genetic data are largely congruent with traditional taxonomy, we found strong evidence supporting the presence of previously unrecognized species in six of the 18 sampled taxa. Strong nodal support and overall congruence among independent loci suggest long-term reproductive isolation among most species-level lineages. While some Melanohalea taxa are truly widespread, a limited number of clades appear to have much more restricted distributional ranges. In most instances the concatenated gene tree and multilocus species tree approaches provided similar estimates of relationships. However, nodal support was generally higher in the phylogeny estimated from concatenated data, and relationships among taxa within one major clade were largely unresolved in the species tree. This study contributes to our understanding of diversity and evolution in common lichen-forming fungi by incorporating multiple locus sequence data to circumscribe morphologicallly cryptic lineages and infer relationships within a coalescent-based species tree approach.

A phylogenetic analysis of the boreal lichen Mycoblastus sanguinarius (Mycoblastaceae, lichenized Ascomycota) reveals cryptic clades correlated with fatty acid profiles.

Graphical abstract Highlights ► The ‘bloody heart lichen’ Mycoblastus sanguinarius consists of two, widespread, cryptic species. ► Mycoblastus sanguinarioides, previously thought confined to Tasmania, is widely distributed. ► Low level clades within both of the cryptic species are correlated with fatty acid profiles. ► Early chemical differentiation may play a role in incipient speciation events.

Global assessment of genetic variation and phenotypic plasticity in the lichen-forming species Tephromela atra

Understanding how many species exist and the processes by which they form remains a central topic of ecological and evolutionary biology, but represents a special challenge within microbial groups. The lichen-forming fungi represent one of the best examples in which species evolution and diversity create patterns of high phenotypic plasticity coupled with wide geographic distributions. We sampled the lichen-forming species Tephromela atra and related species at a world-wide scale to reconstruct a phylogenetic hypothesis using three nuclear markers. Samples were also studied for morphological and chemical traits to assess how well the phenotypic relationships with species, previously segregated from T. atra, agrees with molecular data. We used a genealogical concordance approach and identified 15 monophyletic clades, which may represent independent lineages. By combining morphological and chemical characters, ecological preferences and geographic origin we distinguish six different species. Although subtle phenotypical traits are frequently used for describing previously cryptic species in fungi, the continuum of variability found in morphology and chemical patterns in T. atra prevents the description of new taxa with characteristic traits. We observed that phenotypic characters arise in parallel at local or regional scale but are not correlated with genetic isolation. Therefore, they are insufficient for characterizing species with broad geographic ranges within T. atra.

Expanded taxon sampling disentangles evolutionary relationships and reveals a new family in Peltigerales (Lecanoromycetidae, Ascomycota)

Lichens that incorporate cyanobacterial symbionts (cyanolichens) are an ecologically key group of species used as biomonitors at all latitudes. Cyanolichen evolution is however based on intense studies of few keystone species and the bulk of species diversity, especially of small species in cold climates, has yet to be accounted for in phylogenetic studies. We assembled an expanded data set including members of all nine currently accepted Peltigeralean families as well as hitherto undersampled representatives of small, radially symmetrical, placodioid cyanolichen genera from the Northern and Southern Hemispheres. Bayesian and maximum likelihood consensus trees from our multilocus analyses (nuSSU, nuLSU and mtSSU) recovered the genera Koerberia, Vestergrenopsis and Steinera as a new, fully supported, family-level clade within the Peltigerales. This clade is further supported by a posteriori morphological analysis and we describe it here as the new family Koerberiaceae. The recently described and physiognomically similar genus Steineropsis, by contrast, is recovered as sister to Protopannaria in the Pannariaceae (Collematineae). Previous analyses have recovered strong monophyletic groups around Pannariaceae, Lobariaceae and Peltigeraceae. We discuss in detail the phylogenetic relationships of all these taxa, provide a pan-Peltigeralean overview of phenotypic characteristics and illustrate all major ascus apical structures. Our topology provides strong backbone support for the sister relationship of Peltigerineae to Collematineae as well as for most currently recognized families of the Peltigerales. The following new combinations are made: Steinera symptychia (Tuck.) T. Sprib. & Muggia, and Vestergrenopsis sonomensis (Tuck.) T. Sprib. & Muggia.

Gyalectoid Pertusaria species form a sister-clade to Coccotrema (Ostropomycetidae, Ascomycota) and comprise the new lichen genus Gyalectaria

The phylogeny and taxonomic placement of three species currently placed in the genus Pertusaria with gyalectoid ascomata were studied using maximum likelihood and Bayesian analysis of four molecular loci (mitochondrial SSU, nuclear LSU rDNA and the protein-coding, nuclear RPB1 and MCM7 genes). A total of 40 new sequences were generated for this study and aligned with 84 sequences retrieved from Genbank. Our results show that the gyalectoid Pertusaria species are only distantly related to Pertusaria s.str. They form a strongly supported sister-group relationship to Coccotrema. Consequently, the new genus Gyalectaria Schmitt, Kalb & Lumbsch is described in Coccotremataceae to accommodate these species and the new combinations G. diluta (C. Björk, G. Thor & T. Wheeler) Schmitt, T. Sprib. & Lumbsch, G. gyalectoides (Vezda) Schmitt, Kalb & Lumbsch, and G. jamesii (Kantvilas) Schmitt, Kalb & Lumbsch are proposed. The order Pertusariales is reduced to synonymy with Agyriales.

Diagnostics for a troubled backbone: testing topological hypotheses of trapelioid lichenized fungi in a large-scale phylogeny of Ostropomycetidae (Lecanoromycetes)

Trapelioid fungi constitute a widespread group of mostly crust-forming lichen mycobionts that are key to understanding the early evolutionary splits in the Ostropomycetidae, the second-most species-rich subclass of lichenized Ascomycota. The uncertain phylogenetic resolution of the approximately 170 species referred to this group contributes to a poorly resolved backbone for the entire subclass. Based on a data set including 657 newly generated sequences from four ribosomal and four protein-coding gene loci, we tested a series of a priori and new evolutionary hypotheses regarding the relationships of trapelioid clades within Ostropomycetidae. We found strong support for a monophyletic group of nine core trapelioid genera but no statistical support to reject the long-standing hypothesis that trapelioid genera are sister to Baeomycetaceae or Hymeneliaceae. However, we can reject a sister group relationship to Ostropales with high confidence. Our data also shed light on several long-standing questions, recovering Anamylopsoraceae nested within Baeomycetaceae, elucidating two major monophyletic groups within trapelioids (recognized here as Trapeliaceae and Xylographaceae), and rejecting the monophyly of the genus Rimularia. We transfer eleven species of the latter genus to Lambiella and describe the genus Parainoa to accommodate a previously misunderstood species of Trapeliopsis. Past phylogenetic studies in Ostropomycetidae have invoked “divergence order” for drawing taxonomic conclusions on higher level taxa. Our data show that if backbone support is lacking, contrasting solutions may be recovered with different or added data. We accordingly urge caution in concluding evolutionary relationships from unresolved phylogenies.

Molecular support for the recognition of the Mycoblastus fucatus group as the new genus Violella (Tephromelataceae, Lecanorales).

The crustose lichen genus Mycoblastus in the Northern Hemisphere includes eight recognized species sharing large, simple ascospores produced 1-2 per ascus in strongly pigmented biatorine apothecia. The monophyly of Mycoblastus and the relationship of its various species to Tephromelataceae have never been studied in detail. Data from ITS rDNA and the genes coding for translation elongation factor 1-α and DNA replication licensing factor mini-chromosome maintenance complex 7 support the distinctness of Mycoblastus s. str. from the core of the Tephromelataceae, but recover M. fucatus and an undescribed Asian species as strongly supported within the latter group. We propose accommodating these two species in a new genus, Violella, which is characterized by its brownish inner ascospore walls, Fucatus-violet hymenial pigment granules and secondary chemistry, and discuss the position of Violella relative to Calvitimela and Tephromela. We describe the new species Violella wangii T. Sprib. & Goffinet to accommodate a new species with roccellic acid from Bhutan, China, India and the Russian Far East. We also exclude Mycoblastus indicus Awasthi & Agarwal from the genus Mycoblastus and propose for it the new combination Malmidea indica (Awasthi & Agarwal) Hafellner & T. Sprib.

Escape from the cryptic species trap: lichen evolution on both sides of a cyanobacterial acquisition event

Large, architecturally complex lichen symbioses arose only a few times in evolution, increasing thallus size by orders of magnitude over those from which they evolved. The innovations that enabled symbiotic assemblages to acquire and maintain large sizes are unknown. We mapped morphometric data against an eight‐locus fungal phylogeny across one of the best‐sampled thallus size transition events, the origins of the Placopsis lichen symbiosis, and used a phylogenetic comparative framework to explore the role of nitrogen‐fixing cyanobacteria in size differences. Thallus thickness increased by >150% and fruiting body core volume increased ninefold on average after acquisition of cyanobacteria. Volume of cyanobacteria‐containing structures (cephalodia), once acquired, correlates with thallus thickness in both phylogenetic generalized least squares and phylogenetic generalized linear mixed‐effects analyses. Our results suggest that the availability of nitrogen is an important factor in the formation of large thalli. Cyanobacterial symbiosis appears to have enabled lichens to overcome size constraints in oligotrophic environments such as acidic, rain‐washed rock surfaces. In the case of the Placopsis fungal symbiont, this has led to an adaptive radiation of more than 60 recognized species from related crustose members of the genus Trapelia. Our data suggest that precyanobacterial symbiotic lineages were constrained to forming a narrow range of phenotypes, so‐called cryptic species, leading systematists until now to recognize only six of the 13 species clusters we identified in Trapelia.