SG: Combining phylogenetic and network analyses for the study of symbiotic systems: a case study using lichens

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Symbioses, which are physically close associations of species including positive (mutualism) and negative (parasitism) interactions, are more the rule than the exception in nature. Virtually all species, including humans, have been and continue to be strongly influenced by symbioses. Ultimately, a comprehensive understanding of the history of life on Earth requires the detailed understanding of the evolutionary and ecological forces shaping species symbioses. The over-arching goal of this research project is to integrate evolutionary (genealogical) and ecological (species interactions) network analyses to test hypotheses about the origins and control of symbiotic associations. This work will focus on the evolution of specificity between symbiotic partners (generalists vs. specialists) using lichen symbioses as a model system. The project builds on a great deal of prior genetic analyses, which have been conducted on over 700 symbiotic associations between fungal and algal species, which give rise to lichens. This project will also provide opportunities for postdoc and undergraduate student training, and will develop non-technical web pages outlining the project to be made available to the public. There will also be professional symposia on the development of novel computational methods for studying symbioses. High school students will be invited to participate in this project based on their interest in a general workshop on lichen symbioses that will be organized. The datasets and phylogenetic results generated by previous studies, provide a unique opportunity to address the following objectives of this study: (1) conduct a network analysis to reveal the association trends of the two mutualistic partners giving rise to lichens, and to infer the most important contributing factors to those associations; (2) compare these results from lichens with other fungal-photoautotrophic systems (e.g., mycorrhizae, endophytes); and (3) design new phylogenetic methods to study the evolution of specificity of interacting fungi and cyanobacteria or algae, and to identify factors correlated with shifts in specificity toward lower or higher specificity in species associations (generalists or specialists). This project is expected to advance the field by coupling the inferential power of phylogenetics with ecological network theory to study symbiotic associations among species within lichens. This new approach for what may be called eco-phylogenetic analysis will estimate, for the first time, the contribution of biotic and abiotic factors through time that best explain the patterns of symbiotic associations observed in nature. The methods developed will be applicable to other symbioses, beyond lichens.