Overview of Phylogenetic Approaches to Mycorrhizal Biogeography, Diversity and Evolution

Neogene speciation and Pleistocene expansion of the genus Pseudephebe (Parmeliaceae, lichenized fungi) involving multiple colonizations of Antarctica

Widespread geographic distributions in lichens have been usually explained by the high dispersal capacity of their tiny diaspores. However, recent phylogenetic surveys have challenged this assumption and provided compelling evidence for cryptic speciation and more restricted distribution ranges in diverse lineages of lichen-forming fungi. To evaluate these scenarios, we focus on the fungal genus Pseudephebe (Parmeliaceae) which includes amphitropical species, a distribution pattern whose origin has been a matter of debate since first recognized in the nineteenth century. In our study, a six-locus dataset and a broad specimen sampling covering almost all Earth's continents is used to investigate species delimitation in Pseudephebe. Population structure, gene flow and dating analyses, as well as genealogical reconstruction methods, are employed to disentangle the most plausible transcontinental migration routes, and estimate the timing of the origin of the amphitropical distribution and the Antarctic populations. Our results demonstrate the existence of three partly admixed phylogenetic species that diverged between the Miocene and Pliocene, and whose Quaternary distribution has been strongly driven by glacial cycles. Pseudephebe minuscula is the only species showing an amphitropical distribution, with populations in Antarctica, whereas the restricted distribution of P. pubescens and an undescribed Alaskan species might reflect the survival of these species in European and North American refugia. Our microevolutionary analyses suggest a Northern Hemisphere origin for P. minuscula, which could have dispersed into the Southern Hemisphere directly and/or through "mountain-hopping" during the Pleistocene. The Antarctic populations of this species are sorted into two genetic clusters: populations of the Antarctic Peninsula were grouped together with South American ones, and the Antarctic Continental populations formed a second cluster with Bolivian and Svalbard populations. Therefore, our data strongly suggest that the current distribution of P. minuscula in Antarctica is the outcome of multiple, recent colonizations. In conclusion, our results stress the need for integrating species delimitation and population analyses to properly approach historical biogeography in lichen-forming fungi.

Significance of Perylene for Source Allocation of Terrigenous Organic Matter in Aquatic Sediments

Perylene is a frequently abundant, and sometimes the only polycyclic aromatic hydrocarbon (PAH) in aquatic sediments, but its origin has been subject of a longstanding debate in geochemical research and pollutant forensics because its historical record differs markedly from typical anthropogenic PAHs. Here we investigate whether perylene serves as a source-specific molecular marker of fungal activity in forest soils. We use a well-characterized sedimentary record (1735-1999) from the anoxic-bottom waters of the Pettaquamscutt River basin, RI to examine mass accumulation rates and isotope records of perylene, and compare them with total organic carbon and the anthropogenic PAH fluoranthene. We support our arguments with radiocarbon (¹⁴C) data of higher plant leaf-wax n-alkanoic acids. Isotope-mass balance-calculations of perylene and n-alkanoic acids indicate that ∼40% of sedimentary organic matter is of terrestrial origin. Further, both terrestrial markers are pre-aged on millennial time-scales prior to burial in sediments and are insensitive to elevated ¹⁴C concentrations following nuclear weapons testing in the mid-20^th Century. Instead, changes coincide with enhanced erosional flux during urban sprawl. These findings suggest that perylene is definitely a product of soil-derived fungi, and a powerful chemical tracer to study the spatial and temporal connectivity between terrestrial and aquatic environments.

Fungal mitochondrial genomes and genetic polymorphisms

Mitochondria are the powerhouses of eukaryotic cells, responsible for ATP generation and playing a role in a diversity of cellular and organismal functions. Different from the majority of other intracellular membrane structures, mitochondria contain their own genetic materials that are capable of independent replication and inheritance. In this mini-review, we provide brief summaries of fungal mitochondrial genome structure, size, gene content, inheritance, and genetic variation. We pay special attention to the relative genetic polymorphisms of the mitochondrial vs nuclear genomes at the population level within individual fungal species. Among the 20 species/groups of species reviewed here, there is a range of variation among genes and species in the relative nuclear and mitochondrial genetic polymorphisms. Interestingly, most (15/20) showed a greater genetic diversity for nuclear genes and genomes than for mitochondrial genes and genomes, with the remaining five showing similar or slower nuclear genome genetic variations. This fungal pattern is different from the dominant pattern in animals, but more similar to that in plants. At present, the mechanisms for the variations among fungal species and the overall low level of mitochondrial sequence polymorphisms are not known. The increasing availability of population genomic data should help us reveal the potential genetic and ecological factors responsible for the observed variations.