The introduction of high-throughput sequencing and omics has expanded the toolkit available for lichen researchers. Genomic, transcriptomic and proteomic data from lichens can now be produced and interrogated relatively easily. Here, we discuss several areas within lichen biology, which have benefited from these methods. These include evolutionary biology of lichen symbionts, their biochemistry, and studies on lichen organismal composition. We discuss metagenomics as one of the most powerful methods to explore lichens as complex symbiotic organisms. Based on recent advances in biological methods, as well as current knowledge gaps in lichen biology, we propose several opportunities for research on the lichen symbiosis, such as studies of spatial organization of lichen thalli and a way to complement data-driven hypothesis-generating omics research with experimental approaches.

This study investigated the population dynamics of the symbiotic pea crab Austinixa aidae and its non-obligate host, the ghost shrimp Callichirus corruptus, on a sandy beach in Northeast Brazil, assessing the influence of the symbiotic relationship and environmental conditions on population traits. Monthly collections were conducted over 1 year at Cinelândia Beach, Aracaju, Sergipe, and specimens of both sexes were sexed and measured from individual burrows. We analysed size–frequency distributions, sex ratios, and reproductive periods, correlating them with each other and with environmental factors. A. aidae showed continuous seasonal reproduction, with peaks between June and August and in April, positively influenced by precipitation (the rainy season). Conversely, the host, C. corruptus, exhibited seasonal reproduction, peaking in February, which was correlated with higher temperatures (the dry season). This antagonistic reproductive pattern between the symbiont and host was confirmed by a significant negative correlation between their respective percentages of ovigerous females. Furthermore, a significant positive correlation was found between the number and size of crabs and the size of their host. Both species displayed smaller sizes than populations at higher latitudes, suggesting a latitudinal influence. This reproductive asynchrony may represent a coevolved strategy for the symbiont to avoid competition for resources during the host’s reproductive peak.

The Bermudan Archipelago supports a high-latitude subtropical coral reef ecosystem ∼1500 km from the nearest major reef system in the Tropical Western Atlantic (TWA) and Greater Caribbean. Although isolated, Bermuda has low rates of marine endemism due to regular long-distance dispersal from the TWA via the Gulf Stream Current. Nevertheless, Bermuda’s coral reef biodiversity is a reduced subset of that in the Greater Caribbean, indicating that its isolation does limit some species from dispersing or establishing persistent populations. The Alpheus armatus Rathbun, 1901 species complex is a clade of five pistol snapping shrimp species that form obligate symbioses with sea anemones from the TWA and Greater Caribbean. Although their host anemones are abundant, no members of this complex are known from Bermuda. We provide the first report of the A. armatus species complex from Bermudan coral reefs. Using molecular approaches, we identified our observed individual as Alpheus immaculatus Knowlton and Keller, 1983. Phylogenetic and species delimitation analyses indicate that our A. immaculatus sample from Bermuda does not represent a cryptic lineage nor genetically differentiated population. Instead, we interpret this species to have arrived recently as a chance long-distance dispersal event. No other A. immaculatus individuals were observed, suggesting this species has not been able to establish a long-term population in Bermuda.

Soil biodiversity is crucial to the maintenance of multiple critical ecosystem functions and services. However, remarkably little is known about the conservation status of most soil-dependent species. To better understand the current situation, we determined the number of soil-dependent species listed in the various categories of the IUCN Red List of Threatened Species. Firstly, a definition of soil-dependent species was developed for IUCN Red List purposes, and this definition facilitated the identification of 8,653 currently listed soil-dependent species. These species included 503 invertebrate and fungal species assessed during the current study; these species were chosen as they were based on priorities for the Red List Strategic Plan, and IUCN Species Survival Commission (SSC) Specialist Group interests. We discuss progress and constraints on the IUCN Red List assessment of soil-dependent species worldwide. Our recommendations for the IUCN SSC to improve the IUCN Red List as a source of information on conservation of soil-dependent species are: (1) scaling up of SSC assessment processes for soil-dependent invertebrates and fungi, including establishment of a Soil Biota Working Group, in line with the IUCN Red List Strategic Plan; (2) building closer connections with other organizations and agencies researching and monitoring soil biodiversity; and (3) broader engagement with and education of governments, landholders and the public as to the fundamental importance of the conservation of global soil biodiversity.

The crustose cyanolichen Fuscopannaria frullaniae (syn. Moelleropsis nebulosa subsp. frullaniae) is a poorly understood taxon that occurs on mosses and liverworts, described from eastern Canada and reported from the Iberian Peninsula, Macaronesia and the eastern USA. Originally placed in the genus Moelleropsis, the position of the species has been debated in the absence of sexual fruiting structures and, until now, DNA sequences from the fungal symbiont. We produced nine sequences from two fungal ribosomal loci from F. frullaniae collected at five different localities in Nova Scotia, Canada and North Carolina, USA. Initial BLASTn queries against public databases revealed high similarity between these sequences and basidiomycete sequences from the Dictyonema clade in Hygrophoraceae, specifically from the genus Acantholichen. We did not obtain ascomycete sequences from any locus or specimen. Phylogenetic analyses recovered the obtained sequences within the broader Acantholichen clade. We conclude that the lichen fungal symbiont is in fact a basidiomycete and introduce for it the new combination Acantholichen frullaniae. Acantholichen frullaniae is the first species of the genus to possess a granular, crustose thallus. The species lacks the characteristic, spiny, balloon-shaped cells called acanthohyphidia that are found in other species of the genus, though it possesses similar, albeit spineless cells on the surface of thallus granules; we suggest that these structures within the wider genus are homologous and represent spiny or smooth cystidia. Numerous samples yielded evidence of basidiospores and basidia produced from thallus granules, evident only after treatment with diluted potassium hydroxide, representing the first sexual structures reported in the genus. We discuss the possible reasons for this, as well as the ecology and threats to the species across its Canadian populations.

This work attempts to better understand the significance of morphological diversity among fungal-algal contact zones present in lichens. We used TEM to examine a variety of lichen symbioses involving non-trebouxialean green algae that show intraparietal penetration by the mycobiont. A principal focus was on Endocarpon pusillum, a well-known member of a family (Verrucariaceae; Eurotiomycetes) previously reported to be characterized by unwalled haustoria exposing a naked fungal protoplast. Peg-like haustoria arose from an inner layer(s) of the mycobiont cell wall that broke through outer layers and penetrated a short distance into the wall of the green algal symbiont (Diplosphaera). In both fungal and algal cells at the contact interface, lomasome-like vesicles and tubules occurred as modifications of the plasmalemma intermixed with wall materials at the inner surface of the cell wall. A fungal cell wall was consistently present around the haustorium, which resembled those depicted in earlier TEM studies of Verrucariaceae. Previously published micrographs of Verrucariaceae purporting to show wall-less haustoria surrounded by an empty space are believed to have been misinterpreted. However, in the isidiose Porina and foliicolous Calopadia, Byssoloma and Fellhanera species (Lecanoromycetes), we did observe extreme degrees of reduction in the mycobiont cell wall at symbiont contact interfaces. In those lichens, a broad area of the fungal cell bulged into the adjacent algal symbiont, broadly invaginating the wall of the latter and penetrating it intraparietally without differentiation of a distinct haustorial structure. The mycobiont wall surrounding such protrusions often thinned to near indistinguishability towards its extremity. The protrusion made direct contact with the algal cell wall; no empty space occurred between them. We propose that the short, peg-like intraparietal haustoria bind the symbionts and help maintain cell contacts amid the stresses of tissue expansion and shrinkage, thereby avoiding disruption of the continuous hydrophobic coating that facilitates transfer between them. Broader contact interfaces with extremely thin adjacent walls may facilitate solute flow between symbionts. Reciprocal penetration of algal protrusions into mycobiont cells, noted in Porina as well as other lichens studied previously, is a neglected but potentially significant indication that both symbionts may actively work to maintain functional contact interfaces.

Feather stars (Echinodermata: Crinoidea) are known to host a diversified associated fauna. Surprisingly, very few accounts on the crinoid epiphytic communities from the coasts of the India are available. The present contribution reports for the first time the crinoid-associated scale worm Paradyte crinoidicola (Potts, 1910) from Gujarat coastline, India. The species has been so far recorded from the southern part of Indian subcontinent, the Lakshadweep Islands as its first record from Indian coastline. Further research and documentation of these species will contribute to enhance our understanding of the diverse associations and complex interactions within Indian marine ecosystems. This highlights the necessity for more thorough field surveys and ongoing monitoring, as the region remains surprisingly underexplored.

Barnacles of the genus Conopea are obligate epibionts of gorgonians and antipatharians. The species Conopea saotomensis Carrison-Stone et al. 2013, previously only known from the islands of São Tomé and Príncipe and the coast of Gabon, is reported from the Bijagós archipelago, Guinea-Bissau, based on morphological examination and DNA barcoding of specimens. The new record extends the known range of the species about 3000 km to the northwest.

While the diversity of foliicolous lichen-forming fungi has been explored in substantial depth, relatively little attention has been paid to their algal symbionts. We studied the unicellular green phycobionts of the lecanoralean lichens Bacidina (Ramalinaceae), Byssoloma, Fellhanera and Tapellaria (Pilocarpaceae) and graphidalean Gyalectidium (Gomphillaceae) from two extratropical foliicolous communities in continental Spain and the Canary Islands. We examined the pyrenoids of algal symbionts within thalli using TEM, and obtained several algal nrSSU and rbcL sequences from whole thalli, and also from cultures isolated from some of these lichens. Pyrenoid structure and molecular sequence data provided support for recognizing Chloroidium (Watanabeales, Trebouxiophyceae) as phycobiont in thalli of Byssoloma subdiscordans and Fellhanera bouteillei (Pilocarpaceae) in both communities. Bacidina apiahica (Ramalinaceae) and Tapellaria epiphylla (Pilocarpaceae) likewise appeared to partner with Chloroidium based on the presence of the same pyrenoid type, although we were able to obtain a phycobiont sequence only from a culture isolate of the latter. These results contrast with those obtained previously from a foliicolous lichen community in southern Florida, which revealed only strains of Heveochlorella (Jaagichlorella) as phycobiont of foliicolous Pilocarpaceae and Gomphillaceae. On the other hand, the pyrenoid we observed in the phycobionts associated with Gyalectidium setiferum and G. minus corresponded to that of Heveochlorella (Jaagichlorella). However, the poor quality of the phycobiont sequence data obtained from G. minus, probably due to the presence of epibiontic algae, could not provide additional perspective on the pyrenoid structure observations. Nonetheless, clear differences in pyrenoid ultrastructure can allow Chloroidium and Heveochlorella phycobionts to be distinguished from each other in TEM. Our results indicate a greater diversity of unicellular green-algal symbionts in foliicolous communities from Spain than previously observed in other geographical areas, and suggest that further studies focused on symbiont pairing in these communities might reveal distinctive and varied patterns of phycobiont preference.

An increasing number of studies are describing the diversity of lichen phycobionts, which is leading to a better understanding of how lichen communities are assembled at different taxonomic, evolutionary and geographical scales. The present study explores the identity and genetic diversity of the microalgal partners of Punctelia borreri and P. subrudecta, two tropical and temperate parmelioid lichen fungi that often grow in temperate and Mediterranean forest ecosystems in Europe. Based on a specimen sampling distributed in two climatically divergent regions in the Iberian Peninsula, we found that these mycobionts are associated with Trebouxia gelatinosa, whose identity was also confirmed by an ultrastructural study of the pyrenoid. The bipartite network analysis indicated that each Punctelia species was associated with a different set of low frequency T. gelatinosa infraspecific lineages, whereas the two most abundant phycobiont lineages were shared between both mycobionts. Based on the current sampling, these two algal lineages occur exclusively in one of the two studied regions, which might point towards climate-driven, fine-tuned fungal-algal interactions. Finally, we documented visible symptoms of injury on the thalli in areas likely to have been impacted by air pollution.