BEE: Spatio-temporal factors shaping symbiotic networks: a case study with cyanolichens

Duke University, Durham NC

Investigators

Abstract

Symbiotic interactions, including parasitism, commensalism and mutualism, form complex networks that are common in nature. Ultimately, a more complete understanding of life can be accomplished only through the study of all symbiotically interacting organisms. This study aims to understand the processes that shape those networks using cyanolichens, which are iconic symbioses consisting mainly of mutually beneficial fungi and cyanobacteria. Questions that will be addressed by this project include: Does the abundance of various free-living cyanobacteria in nature dictate the main lichen partner pairs (one fungus, one cyanobacterium) who shape lichen communities? Do broadly distributed cyanobacteria who associate with many fungal species (generalists) do so mostly with closely related fungal species? What are the biomolecules that determine which cyanobacteria interact with which fungal partners? How do the rules of association for lichen partners differ when compared to other symbiotic systems? This project includes training and educational components for graduate and undergraduate students, the dissemination of new methods for innovative research on symbiotic systems, outreach activities, and the development of a new advising model to help underrepresented students interested in science and engineering reach their academic goals. The main focus of this study is to determine how mutualistic networks are shaped by evolution and environmental gradients at different spatial scales. To reach this goal, a fully integrated approach combining evolutionary biology and ecology will be implemented. Recent studies of the lichen model genus Peltigera and its Nostoc symbionts have revealed: (i) that Peltigera species are mostly specialized on generalist Nostoc phylogroups, (ii) that the interactions and the high level of specialization by the fungus are phylogenetically conserved, and (iii) that bioclimatic factors, at an intra-biome scale, are more limiting than cyanobiont availability for explaining geographic distributions of Peltigera species. This study will capitalize on the large-scale, systematic, and multi-taxon, monitoring program of the Alberta Biodiversity Monitoring Institute (ABMI). This project represents a unique opportunity to test three important drivers of symbiotic network assembly: (1) Spatial scales and gradients - Are interactions well predicted by environmental biotic and abiotic properties, and/or spatial overlap due to stochastic dispersal? (2) Phylogenetic history - Do Nostoc symbionts show phylogenetic conservatism in their selection of Peltigera partners, as shown by Peltigera towards their Nostoc partners? (3) Specific recognition molecules - Are Nostoc genes differentially expressed in lichen thalli vs a free-living state, and do they explain the observed specificity between symbiotic partners in nature? This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.