Format: ORAL

Fernando Fernandez-Mendoza1,2, Eva Andrea Strasser2, Ester Gaya3, Martin Grube2

1 Institute of Biomedical Informatics, Technological University of Graz, Graz, Austria. 2 Institute of Biology, Karl-Franzens-Universita¨t Graz, Graz, Austria, 3 Royal Botanic Gardens, Kew, Richmond, UK

The role played by reproductive isolation in fungal speciation remains poorly understood. Several studies, especially based in in vitro experiments, show that some fungi maintain open reproductive boundaries with more or less distantly related species, in a strategy that can be best described as first mate and then figure things out. In nature, however, sexual isolation is shaped by multiple factors that act simultaneously as barriers to the flow of genetic information at different scales and levels of organization. Geographic and ecological boundaries limit gene-flow between populations, while molecular factors implied in recognition, development or simply completeness of gene content, impose limits to the viability of hybrid genotypes. The lichen genus Pyrenodesmia s.s. provides a good example of the limitations of phylogenetic methods of species delimitation, and of the importance of interspecific hybridization in natural populations. The phylogenetic study of Western European specimens of the genus identified widespread interspecific mating, i.e. low pre- zygotic isolation as well as discrepancy in phylogenetic signal linked to hybridization. All species are interconnected in a supraspecific syngameon in which species remain partly distinguishable but also produce hybrids and phenotypically intermediate morphs. Comparative genomics data on selected specimens, provides evidence that genome concertation plays an important role in fungal hybrids. The mechanisms implicated in genome simplification and in the concertation of gene content are still a matter under scrutiny. IN our survey we discuss the role played by heterochromatin related genome defense mechanisms, such as RIP, and the proliferation and silencing of transposable elements in the regionalization of the genome into areas of reduced and increased recombination. We hypothesize that this regionalization is largely responsible for the evolutionary success of this mating strategy, as it allows maintaining a stable core genome while allowing for the incorporation of xenologous genes of adaptive value in subtelomeric regions.