Macroevolution of Specificity in Cyanolichens of the Genus Peltigera Section Polydactylon (Lecanoromycetes, Ascomycota)

The mitogenomes characterization of two Peltigera species (Peltigera elisabethae and Peltigera polydactylon) and comparative mitogenomic analyses of six Peltigera

In the present study, the mitochondrial genomes of Peltigera elisabethae and P. polydactylon were sequenced and assembled. The two mitogenomes were composed of circular DNA molecules, with sizes of 64,034 bp and 59,208 bp, respectively. Comparative analysis showed that the genome size, GC content, GC skew, and AT skew varied between the two mitochondrial genomes. In codon analysis, phenylalanine (Phe), isoleucine (Ile), and leucine (Leu) were most frequently used in six Peltigera genomes. Evolutionary analysis showed that all 14 protein-coding genes (PCGs) were subject to purifying selection in the six Peltigera species. Regarding gene rearrangement, the PCGs of Peltigera had the same gene sequence and gene content, and a few intron sequences and spacer sequences were rearranged in Peltigera. In the phylogenetic analysis, we used Bayesian and ML methods to construct a phylogenetic tree. Two phylogenetic trees with consistent topology with high support indicate that mitochondrial genes were reliable molecular markers for analyzing the phylogenetic relationships. The present study enriches the mitochondrial genome data of Peltigera and promotes further understanding of the genetics and evolution of the Peltigera genus.

Specialization patterns in symbiotic associations: A community perspective over spatial scales

Specialization, contextualized in a resource axis of an organism niche, is a core concept in ecology. In biotic interactions, specialization can be determined by the range of interacting partners. Evolutionary and ecological factors, in combination with the surveyed scale (spatial, temporal, biological, and/or taxonomic), influence the conception of specialization. This study aimed to assess the specialization patterns and drivers in the lichen symbiosis, considering the interaction between the principal fungus (mycobiont) and the associated Nostoc (cyanobiont), from a community perspective considering different spatial scales. Thus, we determined Nostoc phylogroup richness and composition of lichen communities in 11 Nothofagus pumilio forests across a wide latitudinal gradient in Chile. To measure specialization, cyanobiont richness, Simpson's and d' indices were estimated for 37 mycobiont species in these communities. Potential drivers that might shape Nostoc composition and specialization measures along the environmental gradient were analysed. Limitations in lichen distributional ranges due to the availability of their cyanobionts were studied. Turnover patterns of cyanobionts were identified at multiple spatial scales. The results showed that environmental factors shaped the Nostoc composition of these communities, thus limiting cyanobiont availability to establish the symbiotic association. Besides, specialization changed with the spatial scale and with the metric considered. Cyanolichens were more specialized than cephalolichens when considering partner richness and Simpson's index, whereas the d' index was mostly explained by mycobiont identity. Little evidence of lichen distributional ranges due to the distribution of their cyanobionts was found. Thus, lichens with broad distributional ranges either associated with several cyanobionts or with widely distributed cyanobionts. Comparisons between local and regional scales showed a decreasing degree of specialization at larger scales due to an increase in cyanobiont richness. The results support the context dependency of specialization and how its consideration changes with the metric and the spatial scale considered. Subsequently, we suggest considering the entire community and widening the spatial scale studied as it is crucial to understand factors determining specialization.

Sulfur is in the Air: Cyanolichen Marriages and Pollution

Cyanolichens are symbiotic organisms involving cyanobacteria and fungi (bipartite) or with the addition of an algal partner (tripartite). Cyanolichens are known for their heightened susceptibility to environmental pollution. We focus here on the impacts on cyanolichens due to rising air pollution; we are especially interested in the role of sulfur dioxide on cyanolichen biology. Cyanolichens due to air pollution including sulfur dioxide exposure, show symptomatic changes including degradation of chlorophyll, lipid membrane peroxidation, decrease in ATP production, changes in respiration rate, and alteration of endogenous auxins and ethylene production, although symptoms are known to vary with species and genotype. Sulfur dioxide has been shown to be damaging to photosynthesis but is relatively benign on nitrogen fixation which proposes as a hypothesis that the algal partner may be more in harm's way than the cyanobiont. In fact, the Nostoc cyanobiont of sulfur dioxide-susceptible Lobaria pulmonaria carries a magnified set of sulfur (alkane sulfonate) metabolism genes capable of alkane sulfonate transport and assimilation, which were only unraveled by genome sequencing, a technology unavailable in the 1950-2000 epoch, where most physiology- based studies were performed. There is worldwide a growing corpus of evidence that sulfur has an important role to play in biological symbioses including rhizobia-legumes, mycorrhizae-roots and cyanobacteria-host plants. Furthermore, the fungal and algal partners of L. pulmonaria appear not to have the sulfonate transporter genes again providing the roles of ambient-sulfur (alkanesulfonate metabolism etc.) mediated functions primarily to the cyanobacterial partner. In conclusion, we have addressed here the role of the atmospheric pollutant sulfur dioxide to tripartite cyanolichen viability and suggest that the weaker link is likely to be the photosynthetic algal (chlorophyte) partner and not the nitrogen-fixing cyanobiont.

Fisheries restoration: Lessons learnt from four benefit-cost models

Globally, fisheries are in decline and in many parts of the world illegal fishing is a major cause of these declines. Ecological restoration of fisheries needs to be promoted, inter alia through improved enforcement, but, which method is the most successful at improving fish stocks, as well as having the highest economic returns? We compare one open-loop (without feedback) and three closed-loop (with feedback) benefit–cost models representing different restoration interventions aimed at promoting compliance. The hybrid systems methodology has been utilized, combining system dynamics, systems archetypes, mathematical differential equations and economic benefit–cost methodologies. The model is tested with reference to a case study of abalone (Haliotis midae) biomass restoration in the Table Mountain National Park marine area (Zone E), Cape Town. Stocks in Zone E have dropped to below the government’s management threshold for sustainable fisheries of 20 percent of the pre-fished levels, and urgent action is required to restore the stocks. According to the model, all proposed restoration interventions produce stock recovery to 100 percent of carrying capacity, well in excess of government targets of 40 percent. Also, all four models had a net present value of greater than zero, indicating substantial positive net benefits to restoration. Each model had specific management recommendations associated with it- greater involvement by the state, capital investment in restoration, changing poacher behavior and entrepreneurship. Although the Post Keynesian and Institutional model produced the highest net returns to restoration over 80 years (Net present value = US$12.66 million at a 6 % discount rate, 2021 prices), all the models are essentially co-evolutionary models, and have merit over different time periods, compliance rates and assumptions around discount rates. While the case study is developed for abalone the findings of the model are likely to be applicable in a wide range of fishery restoration contexts.

Phylogenetic structure of specialization: A new approach that integrates partner availability and phylogenetic diversity to quantify biotic specialization in ecological networks

Biotic specialization holds information about the assembly, evolution, and stability of biological communities. Partner availabilities can play an important role in enabling species interactions, where uneven partner availabilities can bias estimates of biotic specialization when using phylogenetic diversity indices. It is therefore important to account for partner availability when characterizing biotic specialization using phylogenies. We developed an index, phylogenetic structure of specialization (PSS), that avoids bias from uneven partner availabilities by uncoupling the null models for interaction frequency and phylogenetic distance. We incorporate the deviation between observed and random interaction frequencies as weights into the calculation of partner phylogenetic α‐diversity. To calculate the PSS index, we then compare observed partner phylogenetic α‐diversity to a null distribution generated by randomizing phylogenetic distances among the same number of partners. PSS quantifies the phylogenetic structure (i.e., clustered, overdispersed, or random) of the partners of a focal species. We show with simulations that the PSS index is not correlated with network properties, which allows comparisons across multiple systems. We also implemented PSS on empirical networks of host–parasite, avian seed‐dispersal, lichenized fungi–cyanobacteria, and hummingbird pollination interactions. Across these systems, a large proportion of taxa interact with phylogenetically random partners according to PSS, sometimes to a larger extent than detected with an existing method that does not account for partner availability. We also found that many taxa interact with phylogenetically clustered partners, while taxa with overdispersed partners were rare. We argue that species with phylogenetically overdispersed partners have often been misinterpreted as generalists when they should be considered specialists. Our results highlight the important role of randomness in shaping interaction networks, even in highly intimate symbioses, and provide a much‐needed quantitative framework to assess the role that evolutionary history and symbiotic specialization play in shaping patterns of biodiversity. PSS is available as an R package at https://github.com/cjpardodelahoz/pss.

The Role of Photobionts as Drivers of Diversification in an Island Radiation of Lichen-Forming Fungi

Speciation in oceanic islands has attracted the interest of scientists since the 19th century. One of the most striking evolutionary phenomena that can be studied in islands is adaptive radiation, that is, when a lineage gives rise to different species by means of ecological speciation. Some of the best-known examples of adaptive radiation are charismatic organisms like the Darwin finches of the Galapagos and the cichlid fishes of the great African lakes. In these and many other examples, a segregation of the trophic niche has been shown to be an important diversification driver. Radiations are known in other groups of organisms, such as lichen-forming fungi. However, very few studies have investigated their adaptive nature, and none have focused on the trophic niche. In this study, we explore the role of the trophic niche in a putative radiation of endemic species from the Macaronesian Region, the Ramalina decipiens group. The photobiont diversity was studied by Illumina MiSeq sequencing of the ITS2 region of 197 specimens spanning the phylogenetic breadth and geographic range of the group. A total of 66 amplicon sequence variants belonging to the four main clades of the algal genus Trebouxia were found. Approximately half of the examined thalli showed algal coexistence, but in most of them, a single main photobiont amounted to more than 90% of the reads. However, there were no significant differences in photobiont identity and in the abundance of ITS2 reads across the species of the group. We conclude that a segregation of the trophic niche has not occurred in the R. decipiens radiation.

Biodiversity Patterns and Ecological Preferences of the Photobionts Associated With the Lichen-Forming Genus Parmelia

The worldwide, ecologically relevant lichen-forming genus Parmelia currently includes 41 accepted species, of which the Parmelia sulcata group (PSULgp) and the Parmelia saxatilis group (PSAXgp) have received considerable attention over recent decades; however, phycobiont diversity is poorly known in Parmelia s. lat. Here, we studied the diversity of Trebouxia microalgae associated with 159 thalli collected from 30 locations, including nine Parmelia spp.: P. barrenoae, P. encryptata, P. ernstiae, P. mayi, P. omphalodes, P. saxatilis, P. serrana, P. submontana, and P. sulcata. The mycobionts were studied by carrying out phylogenetic analyses of the nrITS. Microalgae genetic diversity was examined by using both nrITS and LSU rDNA markers. To evaluate putative species boundaries, three DNA species delimitation analyses were performed on Trebouxia and Parmelia. All analyses clustered the mycobionts into two main groups: PSULgp and PSAXgp. Species delimitation identified 13 fungal and 15 algal species-level lineages. To identify patterns in specificity and selectivity, the diversity and abundance of the phycobionts were identified for each Parmelia species. High specificity of each Parmelia group for a given Trebouxia clade was observed; PSULgp associated only with clade I and PSAXgp with clade S. However, the degree of specificity is different within each group, since the PSAXgp mycobionts were less specific and associated with 12 Trebouxia spp., meanwhile those of PSULgp interacted only with three Trebouxia spp. Variation-partitioning analyses were conducted to detect the relative contributions of climate, geography, and symbiotic partner to phycobiont and mycobiont distribution patterns. Both analyses explained unexpectedly high portions of variability (99 and 98%) and revealed strong correlations between the fungal and algal diversity. Network analysis discriminated seven ecological clusters. Even though climatic conditions explained the largest proportion of the variation among these clusters, they seemed to show indifference relative to climatic parameters. However, the cluster formed by P. saxatilis A/P. saxatilis B/Trebouxia sp. 2/Trebouxia sp. S02/Trebouxia sp. 3A was identified to prefer cold-temperate as well as humid summer environments.

Turnover of Lecanoroid Mycobionts and Their Trebouxia Photobionts Along an Elevation Gradient in Bolivia Highlights the Role of Environment in Structuring the Lichen Symbiosis

Shifts in climate along elevation gradients structure mycobiont-photobiont associations in lichens. We obtained mycobiont (lecanoroid Lecanoraceae) and photobiont (Trebouxia alga) DNA sequences from 89 lichen thalli collected in Bolivia from a ca. 4,700 m elevation gradient encompassing diverse natural communities and environmental conditions. The molecular dataset included six mycobiont loci (ITS, nrLSU, mtSSU, RPB1, RPB2, and MCM7) and two photobiont loci (ITS, rbcL); we designed new primers to amplify Lecanoraceae RPB1 and RPB2 with a nested PCR approach. Mycobionts belonged to Lecanora s.lat., Bryonora, Myriolecis, Protoparmeliopsis, the "Lecanora" polytropa group, and the "L." saligna group. All of these clades except for Lecanora s.lat. occurred only at high elevation. No single species of Lecanoraceae was present along the entire elevation gradient, and individual clades were restricted to a subset of the gradient. Most Lecanoraceae samples represent species which have not previously been sequenced. Trebouxia clade C, which has not previously been recorded in association with species of Lecanoraceae, predominates at low- to mid-elevation sites. Photobionts from Trebouxia clade I occur at the upper extent of mid-elevation forest and at some open, high-elevation sites, while Trebouxia clades A and S dominate open habitats at high elevation. We did not find Trebouxia clade D. Several putative new species were found in Trebouxia clades A, C, and I. These included one putative species in clade A associated with Myriolecis species growing on limestone at high elevation and a novel lineage sister to the rest of clade C associated with Lecanora on bark in low-elevation grassland. Three different kinds of photobiont switching were observed, with certain mycobiont species associating with Trebouxia from different major clades, species within a major clade, or haplotypes within a species. Lecanoraceae mycobionts and Trebouxia photobionts exhibit species turnover along the elevation gradient, but with each partner having a different elevation threshold at which the community shifts completely. A phylogenetically defined sampling of a single diverse family of lichen-forming fungi may be sufficient to document regional patterns of Trebouxia diversity and distribution.

Opening the Gap: Rare Lichens With Rare Cyanobionts - Unexpected Cyanobiont Diversity in Cyanobacterial Lichens of the Order Lichinales

The last decades of research led to a change in understanding of lichens that are now seen as self-sustaining micro-ecosystems, harboring diverse microbial organisms in tight but yet not fully understood relationships. Among the diverse interdependencies, the relationship between the myco- and photobiont is the most crucial, determining the shape, and ecophysiological properties of the symbiotic consortium. Roughly 10% of lichens associate with cyanobacteria as their primary photobiont, termed cyanolichens. Up to now, the diversity of cyanobionts of bipartite lichens resolved by modern phylogenetic approaches is restricted to the filamentous and heterocytous genera of the order Nostocales. Unicellular photobionts were placed in the orders Chroococcales, Pleurocapsales, and Chroococcidiopsidales. However, especially the phylogeny and taxonomy of the Chroococcidiopsidales genera remained rather unclear. Here we present new data on the identity and phylogeny of photobionts from cyanolichens of the genera Gonohymenia, Lichinella, Peccania, and Peltula from a broad geographical range. A polyphasic approach was used, combining morphological and cultivation-depending characteristics (microscopy, staining techniques, life cycle observation, baeocyte motility, and nitrogen fixation test) with phylogenetic analyses of the 16S rRNA and 16S–23S ITS gene region. We found an unexpectedly high cyanobiont diversity in the cyanobacterial lichens of the order Lichinales, including two new genera and seven new species, all of which were not previously perceived as lichen symbionts. As a result, we describe the novel unicellular Chroococcidiopsidales genera Pseudocyanosarcina gen. nov. with the species Pseudocyanosarcina phycocyania sp. nov. (from Peltula clavata, Australia) and Compactococcus gen. nov. with the species Compactococcus sarcinoides sp. nov. (from Gonohymenia sp., Australia) and the new Chroococcidiopsidales species Aliterella compacta sp. nov. (from Peltula clavata, Australia), Aliterella gigantea sp. nov. (from Peltula capensis; South Africa), Sinocapsa ellipsoidea sp. nov. (from Peccania cerebriformis, Austria), as well as the two new Nostocales species Komarekiella gloeocapsoidea sp. nov. (from Gonohymenia sp., Czechia) and Komarekiella globosa sp. nov. (from Lichinella cribellifera, Canary Islands, Spain). Our study highlights the role of cyanolichens acting as a key in untangling cyanobacterial taxonomy and diversity. With this study, we hope to stimulate further research on photobionts, especially of rare cyanolichens.

Global Biodiversity Patterns of the Photobionts Associated with the Genus Cladonia (Lecanorales, Ascomycota)

The diversity of lichen photobionts is not fully known. We studied here the diversity of the photobionts associated with Cladonia, a sub-cosmopolitan genus ecologically important, whose photobionts belong to the green algae genus Asterochloris. The genetic diversity of Asterochloris was screened by using the ITS rDNA and actin type I regions in 223 specimens and 135 species of Cladonia collected all over the world. These data, added to those available in GenBank, were compiled in a dataset of altogether 545 Asterochloris sequences occurring in 172 species of Cladonia. A high diversity of Asterochloris associated with Cladonia was found. The commonest photobiont lineages associated with this genus are A. glomerata, A. italiana, and A. mediterranea. Analyses of partitioned variation were carried out in order to elucidate the relative influence on the photobiont genetic variation of the following factors: mycobiont identity, geographic distribution, climate, and mycobiont phylogeny. The mycobiont identity and climate were found to be the main drivers for the genetic variation of Asterochloris. The geographical distribution of the different Asterochloris lineages was described. Some lineages showed a clear dominance in one or several climatic regions. In addition, the specificity and the selectivity were studied for 18 species of Cladonia. Potentially specialist and generalist species of Cladonia were identified. A correlation was found between the sexual reproduction frequency of the host and the frequency of certain Asterochloris OTUs. Some Asterochloris lineages co-occur with higher frequency than randomly expected in the Cladonia species.

Complex Interaction Networks Among Cyanolichens of a Tropical Biodiversity Hotspot

Interactions within lichen communities include, in addition to close mutualistic associations between the main partners of specific lichen symbioses, also more elusive relationships between members of a wider symbiotic community. Here, we analyze association patterns of cyanolichen symbionts in the tropical montane forests of Taita Hills, southern Kenya, which is part of the Eastern Afromontane biodiversity hotspot. The cyanolichen specimens analyzed represent 74 mycobiont taxa within the order Peltigerales (Ascomycota), associating with 115 different variants of the photobionts genus Nostoc (Cyanobacteria). Our analysis demonstrates wide sharing of photobionts and reveals the presence of several photobiont-mediated lichen guilds. Over half of all mycobionts share photobionts with other fungal species, often from different genera or even families, while some others are strict specialists and exclusively associate with a single photobiont variant. The most extensive symbiont network involves 24 different fungal species from five genera associating with 38 Nostoc photobionts. The Nostoc photobionts belong to two main groups, the Nephroma-type Nostoc and the Collema/Peltigera-type Nostoc, and nearly all mycobionts associate only with variants of one group. Among the mycobionts, species that produce cephalodia and those without symbiotic propagules tend to be most promiscuous in photobiont choice. The extent of photobiont sharing and the structure of interaction networks differ dramatically between the two major photobiont-mediated guilds, being both more prevalent and nested among Nephroma guild fungi and more compartmentalized among Peltigera guild fungi. This presumably reflects differences in the ecological characteristics and/or requirements of the two main groups of photobionts. The same two groups of Nostoc have previously been identified from many lichens in various lichen-rich ecosystems in different parts of the world, indicating that photobiont sharing between fungal species is an integral part of lichen ecology globally. In many cases, symbiotically dispersing lichens can facilitate the dispersal of sexually reproducing species, promoting establishment and adaptation into new and marginal habitats and thus driving evolutionary diversification.

Contribution of Cyanotoxins to the Ecotoxicological Role of Lichens

The fascinating world of lichens draws the attention of the researchers because of the numerous properties of lichens used traditionally and, in modern times, as a raw material for medicines and in the perfumery industry, for food and spices, for fodder, as dyes, and for other various purposes all over the world. However, lichens being widespread symbiotic entities between fungi and photosynthetic partners may acquire toxic features due to either the fungi, algae, or cyano-procaryotes producing toxins. By this way, several common lichens acquire toxic features. In this survey, recent data about the ecology, phytogenetics, and biology of some lichens with respect to the associated toxin-producing cyanoprokaryotes in different habitats around the world are discussed. Special attention is paid to the common toxins, called microcystin and nodularin, produced mainly by the Nostoc species. The effective application of a series of modern research methods to approach the issue of lichen toxicity as contributed by the cyanophotobiont partner is emphasized.

New lineages of photobionts in Bolivian lichens expand our knowledge on habitat preferences and distribution of Asterochloris algae

We studied the biodiversity of Asterochloris photobionts found in Bolivian lichens to better understand their global spatial distribution and adaptation strategies in the context of a worldwide phylogeny of the genus. Based on nuclear ITS rDNA, the chloroplast rbcL gene and the actin type I gene we reconstructed a phylogenetic tree that recovered nine new Asterochloris lineages, while 32 Bolivian photobiont samples were assigned to 12 previously recognized Asterochloris lineages. We also show that some previously discovered Asterochloris photobiont species and lineages may occur in a broader spectrum of climatic conditions, and mycobiont species and photobionts may show different preferences along an altitude gradient. To reveal general patterns of of mycobiont specificity towards the photobiont in Asterochloris, we tested the influence of climate, altitude, geographical distance and effects of symbiotic partner (mycobiont) at the species level of three genera of lichen forming fungi: Stereocaulon, Cladonia and Lepraria. Further, we compared the specificity of mycobionts towards Asterochloris photobionts in cosmopolitan, Neotropical, and Pantropical lichen forming fungi. Interestingly, cosmopolitan species showed the lowest specificity to their photobionts, but also the lowest haplotype diversity. Neotropical and Paleotropical mycobionts, however, were more specific.

Functional Traits in Lichen Ecology: A Review of Challenge and Opportunity

Community ecology has experienced a major transition, from a focus on patterns in taxonomic composition, to revealing the processes underlying community assembly through the analysis of species functional traits. The power of the functional trait approach is its generality, predictive capacity such as with respect to environmental change, and, through linkage of response and effect traits, the synthesis of community assembly with ecosystem function and services. Lichens are a potentially rich source of information about how traits govern community structure and function, thereby creating opportunity to better integrate lichens into 'mainstream' ecological studies, while lichen ecology and conservation can also benefit from using the trait approach as an investigative tool. This paper brings together a range of author perspectives to review the use of traits in lichenology, particularly with respect to European ecosystems from the Mediterranean to the Arctic-Alpine. It emphasizes the types of traits that lichenologists have used in their studies, both response and effect, the bundling of traits towards the evolution of life-history strategies, and the critical importance of scale (both spatial and temporal) in functional trait ecology.

Extensive photobiont sharing in a rapidly radiating cyanolichen clade

Recent studies have uncovered remarkable diversity in Dictyonema s.lat. basidiolichens, here recognized as subtribe Dictyonemateae. This group includes five genera and 148 species, but hundreds more await description. The photobionts of these lichens belong to Rhizonema, a recently resurrected cyanobacterial genus known by a single species. To further investigate photobiont diversity within Dictyonemateae, we generated 765 new cyanobacterial sequences from 635 specimens collected from 18 countries. The ITS barcoding locus supported the recognition of 200 mycobiont (fungal) species among these samples, but the photobiont diversity was comparatively low. Our analyses revealed three main divisions of Rhizonema, with two repeatedly recovered as monophyletic (proposed as new species), and the third mostly paraphyletic. The paraphyletic lineage corresponds to R. interruptum and partnered with mycobionts from all five genera in Dictyonemateae. There was no evidence of photobiont-mycobiont co-speciation, but one of the monophyletic lineages of Rhizonema appears to partner predominantly with one of the two major clades of Cora (mycobiont) with samples collected largely from the northern Andes. Molecular clock estimations indicate the Rhizonema species are much older than the fungal species in the Dictyonemateae, suggesting that these basidiolichens obtained their photobionts from older ascolichen lineages and the photobiont variation in extant lineages of Dictyonemateae is the result of multiple photobiont switches. These results support the hypothesis of lichens representing "fungal farmers," in which diverse mycobiont lineages associate with a substantially lower diversity of photobionts by sharing those photobionts best suited for the lichen symbiosis among multiple and often unrelated mycobiont lineages.

Nitrogen-Fixing Bacteria Associated with Peltigera Cyanolichens and Cladonia Chlorolichens

Lichens have been extensively studied and described; however, recent evidence suggests that members of the bacterial community associated with them could contribute new functions to the symbiotic interaction. In this work, we compare the nitrogen-fixing guild associated with bipartite terricolous lichens with different types of photobiont: Peltigera cyanolichens and Cladonia chlorolichens. Since cyanobacteria contribute nitrogen to the symbiosis, we propose that chlorolichens have more diverse bacteria with the ability to fix nitrogen compared to cyanolichens. In addition, since part of these bacteria could be recruited from the substrate where lichens grow, we propose that thalli and substrates share some bacteria in common. The structure of the nitrogen-fixing guild in the lichen and substrate bacterial communities of both lichens was determined by terminal restriction fragment length polymorphism (TRFLP) of the nifH gene. Multivariate analyses showed that the nitrogen-fixing bacteria associated with both types of lichen were distinguishable from those present in their substrates. Likewise, the structure of the nitrogen-fixing bacteria present in the cyanolichens was different from that of chlorolichens. Finally, the diversity of this bacterial guild calculated using the Shannon index confirms the hypothesis that chlorolichens have a higher diversity of nitrogen-fixing bacteria than cyanolichens.

Contrasting Symbiotic Patterns in Two Closely Related Lineages of Trimembered Lichens of the Genus Peltigera

Species circumscription is key to the characterization of patterns of specificity in symbiotic systems at a macroevolutionary scale. Here, a worldwide phylogenetic framework was used to assess the biodiversity and symbiotic patterns of association among partners in trimembered lichens from the genus Peltigera, section Chloropeltigera. We sequenced six loci of the main fungal partner and performed species discovery and validation analyses to establish putative species boundaries. Single locus phylogenies were used to establish the identity of both photobionts, Nostoc (cyanobacterium) and Coccomyxa (green alga). Distribution and specificity patterns were compared to the closely related clade, section Peltidea, which includes mainly Peltigera species with trimembered thalli. For section Chloropeltigera, eight fungal species (including five newly delimited putative species) were found in association with nine Nostoc phylogroups and two Coccomyxa species. In contrast, eight fungal species (including three newly delimited putative species) in section Peltidea were found in association with only four Nostoc phylogroups and the same two Coccomyxa species as for section Chloropeltigera. This difference in cyanobiont biodiversity between these two sections can potentially be explained by a significantly higher frequency of sexual reproductive structures in species from section Chloropeltigera compared to section Peltidea. Therefore, horizontal transmission of the cyanobiont might be more prevalent in Chloropeltigera species, while vertical transmission might be more common in Peltidea species. All Peltigera species in section Chloropeltigera are generalists in their association with Nostoc compared to more specialized Peltigera species in section Peltidea. Constrained distributions of Peltigera species that associate strictly with one species of green algae (Coccomyxa subellipsoidea) indicate that the availability of the green alga and the specificity of the interaction might be important factors limiting geographic ranges of trimembered Peltigera, in addition to constraints imposed by their interaction with Nostoc partners and by climatic factors.

Carbon Consumption Patterns of Microbial Communities Associated with Peltigera Lichens from a Chilean Temperate Forest

Lichens are a symbiotic association between a fungus and a green alga or a cyanobacterium, or both. They can grow in practically any terrestrial environment and play crucial roles in ecosystems, such as assisting in soil formation and degrading soil organic matter. In their thalli, they can host a wide diversity of non-photoautotrophic microorganisms, including bacteria, which play important functions and are considered key components of the lichens. In this work, using the BioLog^® EcoPlate system, we studied the consumption kinetics of different carbon-sources by microbial communities associated with the thallus and the substrate of Peltigera lichens growing in a Chilean temperate rain forest dominated by Nothofagus pumilio. Based on the similarity of the consumption of 31 carbon-sources, three groups were formed. Among them, one group clustered the microbial metabolic profiles of almost all the substrates from one of the sampling sites, which exhibited the highest levels of consumption of the carbon-sources, and another group gathered the microbial metabolic profiles from the lichen thalli with the most abundant mycobiont haplotypes. These results suggest that the lichen thallus has a higher impact on the metabolism of its microbiome than on the microbial community of its substrate, with the latter being more diverse in terms of the metabolized sources and whose activity level is probably related to the availability of soil nutrients. However, although significant differences were detected in the microbial consumption of several carbon-sources when comparing the lichen thallus and the underlying substrate, d-mannitol, l-asparagine, and l-serine were intensively metabolized by both communities, suggesting that they share some microbial groups. Likewise, some communities showed high consumption of 2-hydroxybenzoic acid, d-galacturonic acid, and itaconic acid; these could serve as suitable sources of microorganisms as bioresources of novel bioactive compounds with biotechnological applications.

Strong specificity and network modularity at a very fine phylogenetic scale in the lichen genus Peltigera

Identifying the drivers and evolutionary consequences of species interactions is a major goal of community ecology. Network-based analyses can provide mathematical tools to detect non-random patterns of interactions, and potentially help predicting the consequences of such patterns on evolutionary dynamics of symbiotic systems. Here, we characterize the structure of a lichen network at a very fine phylogenetic scale, by identifying the photosynthetic partners (i.e., cyanobacteria of the genus Nostoc) of lichenized fungi belonging to a monophyletic section of a single genus (i.e., section Polydactylon of the genus Peltigera), worldwide. Even at such a fine phylogenetic scale, we found that interactions were highly modular and anti-nested, indicating strong preferences in interactions. When considering local Peltigera communities, i.e., datasets at small spatial scales with only a slightly broader phylogenetic range, interactions remained modular but were asymmetric, with generalist Nostoc partners interacting with specialized Peltigera species. This asymmetry was not detected with our global spatial scale dataset. We discuss these results in the light of lichen community assembly, and explore how such interaction patterns may influence coevolution in lichens and the evolutionary stability of the mutualism in general.

Sharing of photobionts in sympatric populations of Thamnolia and Cetraria lichens: evidence from high-throughput sequencing

In this study, we explored the diversity of green algal symbionts (photobionts) in sympatric populations of the cosmopolitan lichen-forming fungi Thamnolia and Cetraria. We sequenced with both Sanger and Ion Torrent High-Throughput Sequencing technologies the photobiont ITS-region of 30 lichen thalli from two islands: Iceland and Öland. While Sanger recovered just one photobiont genotype from each thallus, the Ion Torrent data recovered 10-18 OTUs for each pool of 5 lichen thalli, suggesting that individual lichens can contain heterogeneous photobiont populations. Both methods showed evidence for photobiont sharing between Thamnolia and Cetraria on Iceland. In contrast, our data suggest that on Öland the two mycobionts associate with distinct photobiont communities, with few shared OTUs revealed by Ion Torrent sequencing. Furthermore, by comparing our sequences with public data, we identified closely related photobionts from geographically distant localities. Taken together, we suggest that the photobiont composition in Thamnolia and Cetraria results from both photobiont-mycobiont codispersal and local acquisition during mycobiont establishment and/or lichen growth. We hypothesize that this is a successful strategy for lichens to be flexible in the use of the most adapted photobiont for the environment.

Substrates of Peltigera Lichens as a Potential Source of Cyanobionts

Photobiont availability is one of the main factors determining the success of the lichenization process. Although multiple sources of photobionts have been proposed, there is no substantial evidence confirming that the substrates on which lichens grow are one of them. In this work, we obtained cyanobacterial 16S ribosomal RNA gene sequences from the substrates underlying 186 terricolous Peltigera cyanolichens from localities in Southern Chile and maritime Antarctica and compared them with the sequences of the cyanobionts of these lichens, in order to determine if cyanobacteria potentially available for lichenization were present in the substrates. A phylogenetic analysis of the sequences showed that Nostoc phylotypes dominated the cyanobacterial communities of the substrates in all sites. Among them, an overlap was observed between the phylotypes of the lichen cyanobionts and those of the cyanobacteria present in their substrates, suggesting that they could be a possible source of lichen photobionts. Also, in most cases, higher Nostoc diversity was observed in the lichens than in the substrates from each site. A better understanding of cyanobacterial diversity in lichen substrates and their relatives in the lichens would bring insights into mycobiont selection and the distribution patterns of lichens, providing a background for hypothesis testing and theory development for future studies of the lichenization process.

Fungal-algal association patterns in lichen symbiosis linked to macroclimate

Both macroclimate and evolutionary events may influence symbiont association and diversity patterns. Here we assess how climatic factors and evolutionary events shape fungal-algal association patterns in the widely distributed lichen-forming fungal genus Protoparmelia. Multilocus phylogenies of fungal and algal partners were generated using 174 specimens. Coalescent-based species delimitation analysis suggested that 23 fungal hosts are associating with 20 algal species. Principal component analysis (PCA) was performed to infer how fungal-algal association patterns varied with climate. Fungi associated with one to three algal partners whereas algae accepted one to five fungal partners. Both fungi and algae were more specific, associating with fewer partners, in the warmer climates. Interaction with more than one partner was more frequent in cooler climates for both the partners. Cophylogenetic analyses suggest congruent fungal-algal phylogenies. Host switch was a more common event in warm climates, whereas failure of the photobiont to diverge with its fungal host was more frequent in cooler climates. We conclude that both environmental factors and evolutionary events drive fungal and algal evolution in Protoparmelia. The processes leading to phylogenetic congruence of fungi and algae are different in different macrohabitats in our study system. Hence, closely related species inhabiting diverse habitats may follow different evolutionary pathways.