P. D. Crittenden

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.

Connectivity, non-random extinction and ecosystem function in experimental metacommunities.

The spatial insurance hypothesis indicates that connectivity is an important attribute of natural ecosystems that sustains both biodiversity and ecosystem function. We tested the hypothesis by measuring the impact of manipulating connectivity in experimental metacommunties of a natural and diverse microecosystem. Isolation led to the extinction of large-bodied apex predators, subsequently followed by increases in prey species abundance. This trophic cascade was associated with significantly altered carbon and nitrogen fluxes in fragmented treatments. The ecosystem impacts were characteristic of a function debt because they persisted for several generations after the initial loss of connectivity. Local extinctions and disruption of ecosystem processes were mitigated, and even reversed, by the presence of corridors in the connected metacommunities, although these beneficial effects were unexpectedly delayed. We hypothesized that corridors maintained grazer movement between fragments, which enhanced microbial activity, and decomposition in comparison to isolated fragments. Our results indicate that knowledge of habitat connectivity and spatial processes is essential to understand the magnitude and timing of ecosystem perturbation in fragmented landscapes.

Lichen-forming fungi: potential sources of novel metabolites

The challenge for todays pharmaceutical industry lies in the discovery and development of new, pharmacologically active molecules. Metabolites produced by microorganisms, and fungi in particular, are a resource for which the therapeutic potential has been recognized, but one that remains largely unexplored and unexploited. Approximately 20% of all known fungal species are obligate symbionts in lichens; this major group of fungi has been long neglected by mycologists, and overlooked by industry.

Aspects of the ecology of mat-forming lichens.

Lichen species in the genera Cladonia (subgenus Cladina), Cetraria, Stereocaulon and Alectoria are important vegetation components on well-drained terrain and on elevated micro-sites in peatlands in boreal-Arctic regions. These lichens often form closed mats, the component thalli in which grow vertically upwards at the apices and die off in the older basal regions; they are therefore only loosely attached to the underlying soil. This growth habit is relatively unusual in lichens being found in <0.5% of known species. It might facilitate internal nutrienr recycling and higher growth rates and, together with the production of allelochemicals, it might underlie the considerable ecological success of mat-forming lichens; experiments to critically assess the importance of these processes are required. Mat-forming lichens can constitute in excess of 60% of the winter food intake of caribou and reindeer. Accordingly there is a pressing need for data on lichen growth rates, measured as mass increment, in order to help determine the carrying capacity of winter ranges for rhese herbivores and to better predict recovery rates following grazing. Trampling during the snow-free season fragments lichen thalli; mat-forming lichens regenerate very successfully from thallus fragments provided trampling does nor re-occur. Frequent recurrence of trampling creates disturbed habitats from which lichens will rapidly become eliminated consistent with J.P. Grimes CSR strategy theory. Such damage to lichen ground cover has occurred where reindeer or caribou are unable to migrate away from their winter range such as on small islands or where political boundaries have been fenced; it can also occur on summer range that contains a significant lichen component and on winter range where numbers of migrarory animals become excessive. Species of Stereocaulon, and other genera that contain cyanobacteria (most notably Peltigera and Nephroma), are among the principal agents of nitrogen fixation in boreal-arctic regions. Stereocaulon-dominated subarctic woodlands provide excellent model systems in which to investigate the role of lichens in nitrogen cycling. Mat-forming lichens are sensitive indicators of atmospheric deposition partly because they occur in open situations in which they intercept precipitation and particulates directly with minimal modification by vascular plant overstoreys. Data from both the UK and northern Russia are presented to illustrate geographical relationships between lichen chemistry and atmospheric deposition of nitrogen and acidity. The ecology of mat-fotming lichens remains under-researched and good opportunities exist for making significant contributions to this field including areas that relate directly to the management of arctic ungulates.

Reproductive systems: Sex and the single lichen

Most lichenized fungi produce abundant sexual structures, and in many species sexual spores seem to provide the only means of dispersal. For example, 90% of lichens found in Great Britain and Ireland produce ascomata (fruit bodies) containing sexually derived ascospores, whereas only 29% form symbiotic vegetative propagules. Sex in lichenized fungi has been assumed to equate with outcrossing, but failure to induce sexuality in vitro has prevented experimental investigation of their breeding systems.

Anthropogenic metal enrichment of snow and soil in north-eastern European Russia

Trace metal composition of winter snowpack, snow-melt filter residues and top-soil samples were determined along three transects through industrial towns in the Usa basin, North-East Russia: Inta, Usinsk and Vorkuta. Snow was analysed for Ag, Al, As, Ba, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sr and Zn using ICP-MS (Ca and K by F-AAS for Vorkuta only), pH and acidity/alkalinity. Filter residues were analysed for: Al, Ba, Ca, Cd, Cu, K, Mg, Mn, Ni, Pb, Sr and Zn using F-AAS and GF-AAS; top-soil samples were analysed for Ba, Cu, Mg, Mn, Na, Ni, Pb, Sr, Zn using F-AAS. Results indicate elevated concentrations of elements associated with alkaline combustion ash around the coal mining towns of Vorkuta and Inta. There is little evidence of deposition around the gas and oil town of Usinsk. Atmospheric deposition in the vicinity of Vorkuta, and to a lesser extent Inta, added significantly to the soil contaminant loading as a result of ash fallout. Acid deposition was associated with pristine areas whereas alkaline combustion ash near to emission sources more than compensated for the acidity caused by SO2.

Sex and the single lichen.

Most lichenized fungi produce abundant sexual structures, and in many species sexual spores seem to provide the only means of dispersal. For example, 90% of lichens found in Great Britain and Ireland produce ascomata (fruit bodies) containing sexually derived ascospores, whereas only 29% form symbiotic vegetative propagules. Sex in lichenized fungi has been assumed to equate with outcrossing, but failure to induce sexuality in vitro has prevented experimental investigation of their breeding systems.

Growth of the cushion-forming lichen, Cladonia portentosa, at nitrogen-polluted and unpolluted heathland sites

Abstract Biomass increments in the cushion-forming heathland lichen Cladonia portentosa were measured at five heathland sites differing in precipitation acidity, wet nitrogen deposition and annual rainfall. Preweighed thalli were placed in the field to grow; one half of the material was native to the sites and the second half was transplanted from a background site in northernmost Scotland. After 1 year lichens were harvested, weighed and the total N concentration in transplanted lichens was measured in the apical 5 mm of thalli (apices) and in a stratum between 40 and 50 mm from the top (base). Site means for 1 years biomass yield varied between 20 and 60% and relative growth rates (RGRs) (mg mg −1 year −1 ) ranged between 0.13 and 0.43. No significant regional differences in the growth of native lichens were encountered which may have implications for pollution monitoring. Transplanted thalli grew significantly slower than native material suggesting a poor adaptivity to alien environments. Nitrogen concentration in both apices and bases of transplanted lichens increased significantly during the year at those sites subject to high N deposition but, owing to retarded growth at these locations, estimated total N uptake by the lichen (N concentration in the thallus base×mass increment) was broadly similar at all sites. Thus, at the site with the highest wet N deposition load, N input greatly exceeded uptake whereas at the background site the two quantities were similar. In contrast, estimated N uptake in lichens native to each site was similar to the site-specific quantity of wet deposited N.

Effects of nitrogen enrichment on phosphatase activity and nitrogen : phosphorus relationships in Cladonia portentosa.

*Relationships between nitrogen deposition in the UK and phosphomonoesterase (PME) activity and nitrogen (N) and phosphorus (P) concentrations in Cladonia portentosa were quantified to understand factors limiting lichen growth and to further develop biomarkers for N pollution. *Lichen was collected from sites differing either in rates of wet N (NH(4)(+) + NO(3)(-)) deposition or in annual mean N concentration in rainfall based on both measured and modelled data sets. The PME activity, and total N and P concentrations were measured in specific horizontal strata in lichen mats and PME activity in the thallus was located using an enzyme-labelled fluorescent phosphatase substrate. *With an increase in modelled N deposition from 4.1 to 32.8 kg N ha(-1) yr(-1), PME activity, thallus N and N : P ratio increased by factors of 2.3, 1.4 and 1.8, respectively. Correlations with modelled data were generally stronger than with measured data and those with N deposition were stronger than those with N concentration in rainfall. The PME activity was located solely in the lichen fungus in outer regions of the thallus. *Nitrogen enrichment changes lichen N : P ratios from values typical of N limitation (for example, 10) to those indicative of P limitation (for example, 26) driving upregulation of PME activity.

Sex in the extremes: lichen-forming fungi

Lichens are characteristically found in environments subject to extremes of temperature, desiccation and low nutrient status. Despite this sexual structures are often formed in abundance. The underlying mechanisms of sex in lichen-forming fungi are discussed, together with possible ecological reasons for the persistence of sexuality. Special features of lichen sex are highlighted including sex at the limits of life on earth in Antarctica, re-lichenization following sex and dispersal, and the perennial nature of lichen fruiting bodies.