"Population and Evolutionary Biology of Fungal Symbionts", Ascona, Switzerland, 2007

The Topic

Over the past 5-10 years, research on the population and evolutionary genetics of fungal symbionts has begun moving into new directions, reflecting more sophisticated questions and new molecular and analytical tools. Complete genome sequences are now available for a number of fungi and many labs now sequence specific loci in large numbers of geographically distinct strains rather than relying on AFLP or microsatellite loci. Analyses based on the coalescent and Bayesian approaches are replacing those based on allele frequencies. New approaches allow us to replace the question “Has there been gene flow among Asian and South American populations?” with questions such as “How many individuals have been exchanged between Asian and South American populations?”. “Which population was the source and which population was the sink for gene flow?”, and “When did the gene flow occur?”. Similarly, instead of simply identifying cryptic species, the new approaches allow us to order the cryptic species in terms of their ancestral relationships and paths of descent, eg cryptic species Z is descended from cryptic species Y and both are descended from cryptic species X. Through these new approaches we can gain insight into the possible mechanisms that are driving reproductive isolation and speciation. And hypotheses regarding proposed mechanisms can be tested using methods of experimental evolution, which are being applied to fungi with increasing frequency.

The main purpose of this symposium is to synthesize the current state of knowledge across a broad array of fungal symbioses, including those involving plants, humans and other animals, and insects. The key researchers in the area have already been contacted, and most of them have already confirmed their willingness to attend and contribute to the symposium. One goal of the symposium is to identify common biological themes across a broad array of fungal symbioses, including, for example, the importance of gene/genotype flow and range expansion in creating new species, or the role of secondary metabolites in forming and maintaining a symbiosis. A second goal of the symposium is to outline a vision for future research in this area. Participants will be invited to share their ideas on the most important questions that should be addressed during the next 10 years, as well as the most promising systems (symbioses), tools, and approaches that can be used to address these questions. For example, one open question is whether any symbiotic fungi are truly exclusively asexual. There is abundant evidence for cryptic sex in most species, even if the sexual stage has not been identified. But no one can agree on the criteria that are needed to give conclusive evidence for sex in the absence of an observed teleomorph. Would it be better to use an experimental approach or to conduct more intensive surveys of existing populations? Should we rely on empirical data analyses or use modelling approaches? Is it more appropriate to use microsatellites or AFLPs or DNA sequences to prove the existence of sex? Similar questions exist for identification of cryptic species and for understanding speciation processes, such as the relative importance of local adaptation and geographical separation in creating species. It is not clear whether the best approach is to use nuclear or mitochondrial genes, neutral or housekeeping loci, or entire genome sequences to address these questions. Many leading labs are interested in these themes and are moving into this research area and we believe that now is the right time to bring together a critical mass of scientists with the expertise needed to chart the future direction for this research.

We propose to organize the program along three major themes related to the type of symbiosis. The theme “mutualists” will focus on mutualistic interactions between fungi and other eucaryotes, such as mycorrhizal and endosymbiont associations on plants, lichen-forming fungi, and the fungus-growing attine ants. The theme “antagonists” will focus on parasitic and pathogenic interactions with other eukaryotes, including fungi infecting plants, animals, and insects. The theme “commensals” will include examples of Candida albicans on humans and Fusarium oxysporum on herbaceous plants in addition to Phialocephala fortinii on trees. A fourth theme “analytical methods” will cut across the three other themes by incorporating the most recent developments in coalescent and Bayesian analytical methods. In the final sessions of the meeting, a panel composed of four of the speakers and an external moderator will present short (15 minutes) presentations of their vision for the future of research in this area, followed by an open floor discussion where all participants will be invited and encouraged to contribute their ideas. This final session will be recorded and a transcription of the most relevant points will be published on a web site that will be accessible via the internet, along with the Powerpoint slides, abstracts, and poster presentations contributed by each participant.