THe Antarctic Lichens as evoLutionary nIches for microbial diversification

This proposal is designed to capture the diversity of fungi and bacteria residing with the lichen thalli to detect i) taxa which are characterizing the Antarctic lichen symbioses, ii) taxa which are peculiar of extreme environments (and are found both as endolichenic and endolithic), and iii)taxa which are specifically associated with same lichen systems worldwide and would be complementing symbionts. 

Three cosmopolitan and three Antarctic endemic lichen species are selected for sampling and molecular analyses of fungal communities. The cosmopolitan Rhizoplaca melanophthalma, Tephromela atra and Xanthoria elegans are worldwide distributed in alpine environments, grow on the same rock types, and have been ecologically, genetically and phylogenetically well studied and their mycobiont and photobiont isolated in culture. R. melanophthalma generally builds umbilicate (fixed to the substrate by a single central holdfast), squamulose or pulvinate, lumpy thalli. T. atra forms crustose thalli composed by contiguous, flat islands of thallus (areoles) which tightly adhere to the substrate with their entire lower surface. X. elegans has a foliose growth form but the thallus tightly adheres to the rock, resembling a crustose thallus, with narrow, convex, radiating lobes. Buellia frigida, Lecanora fuscobrunnea and Lecidea cancriformis are selected among the endemic Antarctic species because they share the same habitat with the three selected cosmopolitan ones. They all build crustose thalli on rocks and are also well known for their genetic, morphological diversity, phylogenetic relationships, and physiological performance as extremotolerant species under extreme and space-simulated.

This proposal will couple high throughput metabarcode sequencing, phylogenetic, microscopy analyses and culture isolations to reach the following objectives:

-Objective 1: To demonstrate that endemic and cosmopolitan lichen species in Antarctica share "Antarctic lichen myco- and microbiomes" which characterize the Antarctic lichens symbioses and are represented by extermotolerant taxa peculiar of Antarctic extremes, but without specificity for the lichen species hosts.

-Objective 2: To demonstrate that cosmopolitan lichen species both growing in and outside Antarctica do host, additionally to the "Antarctic lichen myco- and microbiome", microbial fractions characterizing of extreme environmental conditions, the “extreme lichen myco- and microbiome”, and has evolved both the endolichenic and endolithic lifestyles to cope with constrained living potentials.

-Objective 3: To demonstrate that different lichens host also an unique, species-specific fungal and bacterial fraction, the “species’ core myco- and microbiome”, which would represent the complementing partnership in the lichen symbioses.

The targeted metabarcoding analyses will consider both a very endemic ecology-specific (three endemic Antarctic lichen species) and an ecology-extended (three cosmopolitan lichen species) taxon sampling of lichens, as well as data obtained by endolithic fungal communities alone, to strengthen the perception that lichen symbioses are characterized by multiple, peculiar and ecologically-shaped myco- and micobiomes. Being the “species’ core myco- and microbiome” a fungal and bacterial fraction, host species-specific, stable and independent from the environmental settings in which the lichen species distributes, it would be considered integrative partnership of the lichen symbiosis, that is incorporated in the thallus or dispersed together with the major lichen symbionts. Higher environmental pressure and selective constrains, worldwide and in Antarctica, would enhance the adaptation to environmental extremes by developing endolichenic and endolithic lifestyles, boosting, therefore, the diversification of taxa inside lichen thalli and rocks. The so generated “extreme lichen myco- and microbiome” would have a diverse taxon composition and would be species-richer than the "species’ core myco- and microbiome", denoting ongoing evolutionary processes. A third fungal fraction would be than represented by taxa which do not have dispersal constrains but have been selected by environmental conditions (“…the environment selects”, Baas Becking 1934) and can survive, more than others, environmental extremes only when growing as endolichenic, such constituting the “Antarctic lichen myco- and microbiome”. Most taxa representatives of the three mycobiomes are expected to occur cryptically and be hardly detected morphologically in the environmental lichen samples, but they could be isolated in axenic culture using accurate methodology.

This research will evidence that lichen thalli are important, pivotal microniches for evolution and diversification of extremotolerant microorganisms in macrohabitats beleaguered by constrained survival potentials, e.g. the continental Antarctica. Furthermore, the isolated strains will represent key material for future in vitro studies to understand species-species interaction and explain reciprocally, whether they may act as helpers or sustainers of the lichen symbioses under extreme environmental conditions.

The proposal also includes:

-Objective 4: To improve the lichen collection of the Italian Antarctic National Museum (Genova) hosted at the University of Trieste with new lichen specimens in order to update the collection and provide fresh material for next, upcoming studies on diversity and biology of Antarctic lichens. Further, all the information that will be gathered during the sampling and the characterization of the specimens will be stored and made available at the database of the MNA Biological Collection Portal.

Sampling during the XXXVII Antarctic Campaign.

Not available so far.