New insights into classification and evolution of the Lecanoromycetes (Pezizomycotina, Ascomycota) from phylogenetic analyses of three ribosomal RNA- and two protein-coding genes

Multiple taxa in the Phoma-complex associate with black elder (Sambucus nigra L.)

The fungus Boeremia sambuci-nigrae (formerly Phoma sambuci-nigrae) causes the corymb wilt disease in elder (Sambucus nigra L.). Here, we assessed the genetic diversity of fungi within the Phoma-complex which associate with commercially cultivated elder in Styria (Austria). We sampled leaves, corymb stalks and berries of elder trees in one organically and in four conventionally managed orchards. In each orchard an area was left untreated allowing a sampling of fungicide treated and untreated trees. Nineteen taxa in the Phoma-complex were isolated and identified based on ITS and LSU nucDNA sequences. One isolate is closely related to Chaetosphaeronema, whereas the majority of the strains belong to the genera Epicoccum and Boeremia in Didymellaceae. Six isolates are monophyletic with Boeremia sambuci-nigrae. The results indicate a varying effectiveness of fungicide treatment for the different fungal groups investigated. The diverse distribution of isolates among the sampling sites suggests the influence of treatment effects and possibly also of climatic conditions.

Phylogenetic placement of the lichenicolous, anamorphic genus Lichenodiplis and its connection to Muellerella-like teleomorphs

Lichenicolous fungi are a specialized group of taxa which inhabit lichens and develop diverse degrees of specificity and parasitic behaviour towards their hosts. They are recognized only by their phenotypic symptoms and sexual or asexual spore-producing structures on the lichen thalli. Only recently, molecular data and culture dependent approaches have helped in uncovering the species diversity and in verifying the phylogenetic position and anamorph-teleomorph relationships of some taxa. Here, we studied the phylogenetic placement of representative taxa of two lichenicolous genera, the coelomycete Lichenodiplis and the ascomycete Muellerella. We obtained molecular data for three nuclear and mitochondrial loci (28S, 18S, and 16S), both from fresh collected specimens and culture isolates. Our multilocus phylogeny places Lichenodiplis and Muellerella samples in one monophyletic, fully supported clade, sister to Epibryon (Epibryaceae) in Chaetothyriales (Eurotiomycetes). Morphological analyses of axenically cultured fungi show the formation of conidiomata and conidiospores in both Lichenodiplis and Muellerella isolates. We suggest that the species Lichenodiplis lecanorae and Muellerella atricola represent, respectively, the anamorphic and teleomorphic stages of the same fungus and discuss their relationships with the other fungal families in Chaetothyriomycetidae.

Photobiont selectivity leads to ecological tolerance and evolutionary divergence in a polymorphic complex of lichenized fungi

BACKGROUND AND AIMS

The integrity and evolution of lichen symbioses depend on a fine-tuned combination of algal and fungal genotypes. Geographically widespread species complexes of lichenized fungi can occur in habitats with slightly varying ecological conditions, and it remains unclear how this variation correlates with symbiont selectivity patterns in lichens. In an attempt to address this question, >300 samples were taken of the globally distributed and ecologically variable lichen-forming species complex Tephromela atra, together with closely allied species, in order to study genetic diversity and the selectivity patterns of their photobionts.

METHODS

Lichen thalli of T. atra and of closely related species T. grumosa, T. nashii and T. atrocaesia were collected from six continents, across 24 countries and 62 localities representing a wide range of habitats. Analyses of genetic diversity and phylogenetic relationships were carried out both for photobionts amplified directly from the lichen thalli and from those isolated in axenic cultures. Morphological and anatomical traits were studied with light and transmission electron microscopy in the isolated algal strains.

KEY RESULTS

Tephromela fungal species were found to associate with 12 lineages of Trebouxia. Five new clades demonstrate the still-unrecognized genetic diversity of lichen algae. Culturable, undescribed lineages were also characterized by phenotypic traits. Strong selectivity of the mycobionts for the photobionts was observed in six monophyletic Tephromela clades. Seven Trebouxia lineages were detected in the poorly resolved lineage T. atra sensu lato, where co-occurrence of multiple photobiont lineages in single thalli was repeatedly observed.

CONCLUSIONS

Low selectivity apparently allows widespread lichen-forming fungi to establish successful symbioses with locally adapted photobionts in a broader range of habitats. This flexibility might correlate with both lower phylogenetic resolution and evolutionary divergence in species complexes of crustose lichen-forming fungi.

Gelatinomyces siamensis gen. sp. nov. (Ascomycota, Leotiomycetes, incertae sedis) on bamboo in Thailand

Gelatinomyces siamensis gen. sp. nov., incertae sedis within Leotiomycetes, the Siamese jelly-ball, is described. The fungus was collected from bamboo culms and branches in Nam Nao National Park, Phetchabun, Thailand. It presents as a ping-pong ball-sized and golf ball-like gelatinous ascostroma. The asci have numerous ascospores, are thick-walled, and arise on discoid apothecia which are aggregated and clustered to form the spherical gelatinous structures. An hyphomycete asexual morph is morphologically somewhat phialophora-like, and produces red pigments. On the basis of phylogenetic analysis based on rRNA, SSU, and LSU gene sequences, the lineage is closest to Collophora rubra. However, ITS sequences place the fungus on a well-separated branch from that fungus, and the morphological and ecological differences exclude it from Collophora.

Journey from the West: did tropical Graphidaceae (lichenized Ascomycota: Ostropales) evolve from a saxicolous ancestor along the American Pacific coast?

PREMISE OF THE STUDY

This study elucidates the phylogenetic position of a unique taxon of Graphidaceae occurring on rock in coastal desert areas, assessing its importance for our understanding of the evolution of the largest family of tropical lichenized fungi. •

METHODS

We used maximum likelihood and Bayesian approaches to reconstruct a three-gene phylogeny of Graphidaceae and a Bayesian molecular clock approach to estimate divergence dates for major clades, as well as Bayesian ancestral ecogeography state analysis. •

KEY RESULTS

The new genus Redonographa represents a new subfamily, Redonographoideae, sister to subfamily Graphidoideae. Redonographa is exclusively saxicolous and restricted to the American Pacific coast from California to central Chile, including Galapagos. It contains four species: Redonographa chilensis comb. nov., R. saxiseda comb. nov., R. saxorum comb. nov., and R. galapagoensis sp. nov. The genus Gymnographopsis, with a similar ecogeography but differing in excipular carbonization and chemistry, is also included in Redonographoideae, with the species G. chilena from Chile and G. latispora from South Africa. Molecular clock analysis indicates that Redonographoideae diverged from Graphidoideae about 132 million years ago (Ma) in the Early Cretaceous. •

CONCLUSIONS

The divergence date for subfamilies Redonographoideae and Graphidoideae coincides with the early breakup of Gondwana and ancient origin of the Atacama Desert. However, the common ancestor of Redonographoideae plus Graphidoideae was reconstructed to be tropical-epiphytic. Thus, even if Redonographoideae is subtropical-saxicolous, the hypothesis that Graphidoideae evolved from a subtropical-saxicolous ancestor is not supported.

A new species of the lenticel fungal genus Claviradulomyces (Ostropales) from the Brazilian Atlantic forest tree Xylopia sericea (Annonaceae)

Claviradulomyces xylopiae sp. nov. is introduced for a fungus occurring in association with abnormal (enlarged, spongy) lenticels of Xylopia sericea (Annonaceae), a common tree of the Atlantic forest and Cerrado ecosystems in Brazil. This is the second species described in the genus and, although it is morphologically distinct from the type species, C. dabeicola from West Africa, it possesses the same characteristics. Apothecial ascomata have periphysoids and paraphyses that are inflated apically (clavate), and ornamented with denticles (raduliform). Furthermore, similar to the type species, it also has long-cylindric or acerose, aseptate ascospores and conidia. An additional asexual morph was produced in culture and is described. Molecular studies of C. dabeicola and the new species confirmed a placement in Ostropales, although a relationship to Odontotremataceae was not supported. Both species were consistently in association with abnormal lenticular development on their woody hosts. It remains to be ascertained, however, if these are the causal agents of the bark disorders, or, simply, opportunistic colonisers. The finding of the second species in the genus Claviradulomyces on a plant from a distantly related family to that of the host of C. dabeicola (Erythroxylaceae) for the genus on a different continent suggests that fungi in this genus may be common on lenticels of other woody plants, and could even have a pantropical distribution. It is possible that fungi in the genus have remained unreported until now because lenticels have remained neglected as a habitat surveyed by mycologists.

Importance of subaerial biofilms and airborne microflora in the deterioration of stonework: a molecular study

The study characterized the sessile microbial communities on mortar and stone in Milan University's Richini's Courtyard and investigated the relationship between airborne and surface-associated microbial communities. Active colonization was found in three locations: green and black patinas were present on mortar and black spots on stone. Confocal laser scanning microscopy, scanning electron microscopy and culture-independent molecular methods revealed that the biofilm causing deterioration was dominated by green algae and black fungi. The mortar used for restoration contained acrylic and siloxane resins that could be used by microorganisms as carbon and energy sources thereby causing proliferation of the biofilm. Epifluorescence microscopy and culture-based methods highlighted a variety of airborne microflora. Bacterial and fungal counts were quantitatively similar to those reported in other investigations of urban areas, the exception being fungi during summer (1-2 orders of magnitude higher). For the first time in the cultural heritage field, culture-independent molecular methods were used to resolve the structure of airborne communities near discoloured surfaces, and to investigate the relationship between such communities and surface-associated biofilms.

Convergent evolution of a symbiotic duet: the case of the lichen genus Polychidium (Peltigerales, Ascomycota)

PREMISE OF THE STUDY

Thallus architecture has long been a powerful guide for classifying lichens and has often trumped photobiont association and ascomatal type, but the reliability of these characters to predict phylogenetic affinity has seldom been tested. The cyanolichen genus Polychidium unites species that have strikingly similar gross morphology but consort with different photobiont genera. If Polychidium were found to be monophyletic, photobiont switching among closely related species would be suggested. If, however, species were found to arise in different lineages, a convergent body plan and ascomatal type evolution would be inferred.

METHODS

We tested the monophyly of Polychidium with a multilocus phylogeny based on nuclear and mitochondrial sequence data from all known Peltigeralean families and reconstructed ancestral states for specific thallus architecture and ascomatal ontogeny types relative to Polychidium and other clades.

KEY RESULTS

We found that Polychidium consists of two species groups that arose independently in different suborders within the Peltigerales, associated with Nostoc and Scytonema photobionts, respectively. We infer from ancestral character state reconstruction that dendroid thallus architecture evolved independently in these two lineages.

CONCLUSIONS

The independent development of similar dendroid thallus architecture in different fungal suborders with different photobionts represents a clear and previously overlooked example of convergent evolution in lichens. Our results also suggest a pattern of character state conservation, loss, and reversion in ascomatal ontogeny types, hitherto considered conserved traits useful for higher level ascomycete systematics.

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.

Disentangling the Collema-Leptogium complex through a molecular phylogenetic study of the Collemataceae (Peltigerales, lichen-forming Ascomycota)

Family Collemataceae (Peltigerales, Ascomycota) includes species of cyanolichens with foliose to fruticose or crustose thalli, with simple or septate ascospores. The current classification divides this family into two groups on the basis of ascospore types. The objective of this study was to evaluate the phylogenetic relationships within this family. Combined DNA sequence data from the nuclear large subunit and mitochondrial small subunit ribosomal RNA genes were used to evaluate monophyly of the family and the relationships between the largest genera of this family. The results revealed that this family is not monophyletic. Genera Staurolemma and Physma, currently classified within the Collemataceae, were found nested within the Pannariaceae. The second result of this study confirms that the genera Collema and Leptogium, both part of the Collemataceae s. str., are not monophyletic and that the presence of a thallus cortex is not a synapomorphy for Leptogium. The main taxonomic conclusion is that families Collemataceae and Pannariaceae were recircumscribed in light of molecular findings with the latter family now including Staurolemma and Physma. Genera Collema and Leptogium form a single mixed monophyletic group. Inferred ancestral character states within the Collema-Leptogium complex revealed that the ancestor of this family had a thallus without cortex and that a cortex evolved at least twice relatively early in the evolution of the Collemataceae s. str. These independent gains of a thallus cortex seems to be associated with a transition from colonizing bare rocks and soils in semi-arid and exposed habitats to epiphytism in shady humid forests.

Symbiotic lifestyle and phylogenetic relationships of the bionts of Mastodia tessellata (Ascomycota, incertae sedis)

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.

Joint dispersal does not imply maintenance of partnerships in lichen symbioses

Dispersal of symbiotic partners by joint propagules is considered as an efficient strategy to maintain successful associations and to circumvent low symbiont availability. Joint dispersal is widespread in diverse symbioses and a particularly common reproductive mode in lichens. We were interested in the implications of joint symbiont dispersal on population genetic structure and investigated patterns of symbiont association in populations of two closely related lichen species in the genus Physconia, with similar range of compatible algal partners. One of the lichen species is characterized by joint dispersal of both symbionts, whereas the other species propagates by meiotic fungal spores alone. The latter species must reestablish the symbiotic stage with appropriate algae sampled from the environment. Both fungal species have specialized on photobionts representing a monophyletic lineage of the algal genus Trebouxia. The results indicate no correlated association of symbiont genotypes in the species with joint symbiont dispersal. We rather show that algal gene diversity in populations of lichenized fungi with different propagation strategies is not necessarily different. The association with algae that differ from the co-dispersed genotypes during the vegetative development of the thalli is the most likely explanation for the observed pattern. Maintenance of symbiotic associations is an option but not a strict consequence of joint symbiont dispersal in lichens.

Fungi evolved right on track

Dating of fungal divergences with molecular clocks thus far has yielded highly inconsistent results. The origin of fungi was estimated at between 660 million and up to 2.15 billion y ago, and the divergence of the two major lineages of higher fungi, Ascomycota and Basidiomycota, at between 390 million y and up to 1.5 billion y ago. Assuming that these inconsistencies stem from various causes, we reassessed the systematic placement of the most important fungal fossil, Paleopyrenomycites, and recalibrated internally unconstrained, published molecular clock trees by applying uniform calibration points. As a result the origin of fungi was re-estimated at between 760 million and 1.06 billion y ago and the origin of the Ascomycota at 500-650 million y ago. These dates are much more consistent than previous estimates, even if based on the same phylogenies and molecular clock trees, and they are also much better in line with the fossil record of fungi and plants and the ecological interdependence between filamentous fungi and land plants. Our results do not provide evidence to suggest the existence of ancient protolichens as an alternative to explain the ecology of early terrestrial fungi in the absence of land plants.

Do lichens domesticate photobionts like farmers domesticate crops? Evidence from a previously unrecognized lineage of filamentous cyanobacteria

Phylogenetic diversity of lichen photobionts is low compared to that of fungal counterparts. Most lichen fungi are thought to be associated with just four photobiont genera, among them the cyanobacteria Nostoc and Scytonema, two of the most important nitrogen fixers in humid ecosystems. Although many Nostoc photobionts have been identified using isolated cultures and sequences, the identity of Scytonema photobionts has never been confirmed by culturing or sequencing. We investigated the phylogenetic placement of presumed Scytonema photobionts and unicellular morphotypes previously assigned to Chroococcus, from tropical Dictyonema, Acantholichen, Coccocarpia, and Stereocaulon lichens. While we confirm that filamentous and unicellular photobiont morphotypes belong to a single clade, this clade does not cluster with Scytonema but represents a novel, previously unrecognized, highly diverse, exclusively lichenized lineage, for which the name Rhizonema is available. The phylogenetic structure observed in this novel lineage suggests absence of coevolution with associated mycobionts at the species or clade level. Instead, highly efficient photobiont strains appear to have evolved through photobiont sharing between unrelated, but ecologically similar, coexisting lineages of lichenized fungi ("lichen guilds"), via the selection of particular photobiont strains through and subsequent horizontal transfer among unrelated mycobionts, a phenomenon not unlike crop domestication.

The Ascomycota tree of life: a phylum-wide phylogeny clarifies the origin and evolution of fundamental reproductive and ecological traits

We present a 6-gene, 420-species maximum-likelihood phylogeny of Ascomycota, the largest phylum of Fungi. This analysis is the most taxonomically complete to date with species sampled from all 15 currently circumscribed classes. A number of superclass-level nodes that have previously evaded resolution and were unnamed in classifications of the Fungi are resolved for the first time. Based on the 6-gene phylogeny we conducted a phylogenetic informativeness analysis of all 6 genes and a series of ancestral character state reconstructions that focused on morphology of sporocarps, ascus dehiscence, and evolution of nutritional modes and ecologies. A gene-by-gene assessment of phylogenetic informativeness yielded higher levels of informativeness for protein genes (RPB1, RPB2, and TEF1) as compared with the ribosomal genes, which have been the standard bearer in fungal systematics. Our reconstruction of sporocarp characters is consistent with 2 origins for multicellular sexual reproductive structures in Ascomycota, once in the common ancestor of Pezizomycotina and once in the common ancestor of Neolectomycetes. This first report of dual origins of ascomycete sporocarps highlights the complicated nature of assessing homology of morphological traits across Fungi. Furthermore, ancestral reconstruction supports an open sporocarp with an exposed hymenium (apothecium) as the primitive morphology for Pezizomycotina with multiple derivations of the partially (perithecia) or completely enclosed (cleistothecia) sporocarps. Ascus dehiscence is most informative at the class level within Pezizomycotina with most superclass nodes reconstructed equivocally. Character-state reconstructions support a terrestrial, saprobic ecology as ancestral. In contrast to previous studies, these analyses support multiple origins of lichenization events with the loss of lichenization as less frequent and limited to terminal, closely related species.

Dissociation and horizontal transmission of codispersing lichen symbionts in the genus Lepraria (Lecanorales: Stereocaulaceae)

Lichenized fungi of the genus Lepraria lack ascomata and conidiomata, and symbionts codisperse by soredia. Here, it is determined whether algal symbionts associated with Lepraria are monophyletic, and whether fungal and algal phylogenies are congruent, both of which are indicative of a long-term, continuous association between symbionts. The internal transcribed spacer (ITS) and part of the actin type I locus were sequenced from algae associated with Lepraria, and the fungal ITS and mitochondrial small subunit (mtSSU) were sequenced from fungal symbionts. Phylogenetic analyses tested for monophyly of algal symbionts and congruence between algal and fungal phylogenies. Algae associated with Lepraria were not monophyletic, and identical algae associated with different Lepraria individuals and species. Algal and fungal phylogenies were not congruent, suggesting a lack of strict codiversification. This study suggests that associations between symbionts are not strictly maintained over evolutionary time. The ability to switch partners may provide benefits similar to genetic recombination, which may have helped this lineage persist.

Phylogenetic comparison of protein-coding versus ribosomal RNA-coding sequence data: A case study of the Lecanoromycetes (Ascomycota)

The resolving power and statistical support provided by two protein-coding (RPB1 and RPB2) and three ribosomal RNA-coding (nucSSU, nucLSU, and mitSSU) genes individually and in various combinations were investigated based on maximum likelihood bootstrap analyses on lichen-forming fungi from the class Lecanoromycetes (Ascomycota). Our results indicate that the optimal loci (single and combined) to use for molecular systematics of lichen-forming Ascomycota are protein-coding genes (RPB1 and RPB2). RPB1 and RPB2 genes individually were phylogenetically more efficient than all two- and three-locus combinations of ribosomal loci. The 3rd codon position of each of these two loci provided the most characters in support of phylogenetic relationships within the Lecanoromycetes. Of the three ribosomal loci we used in this study, mitSSU contributed the most to phylogenetic analyses when combined with RPB1 and RPB2. Except for the mitSSU, ribosomal genes were the most difficult to recover because they often contain many introns, resulting in PCR bias toward numerous and intronless co-extracted contaminant fungi (mainly Dothideomycetes, Chaetothyriomycetes, and Sordariomycetes in the Ascomycota, and members of the Basidiomycota), which inhabit lichen thalli. Maximum likelihood analysis on the combined five-locus data set for 82 members of the Lecanoromycetes provided a well resolved and well supported tree compared to existing phylogenies. We confirmed the monophyly of three recognized subclasses in the Lecanoromycetes, the Acarosporomycetidae, Ostropomycetidae, and Lecanoromycetideae; the latter delimited as monophyletic for the first time, with the exclusion of the family Umbilicariaceae and Hypocenomyce scalaris. The genus Candelariella (formerly in the Candelariaceae, currently a member of the Lecanoraceae) represents the first evolutionary split within the Lecanoromycetes, before the divergence of the Acarosporomycetidae. This study provides a foundation necessary to guide the selection of loci for future multilocus phylogenetic studies on lichen-forming and allied ascomycetes.