DISSERTATION RESEARCH: Tracking trends in the lichen symbiosis: do species interactions drive the latitudinal diversity gradient?

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The latitudinal diversity gradient is the pattern in which many species are found in the tropics, near the equator, and fewer species are found outside of the tropics, towards the North and South poles. This pattern is often explained in terms of temperature, climate, or geological conditions. Less frequently, the latitudinal gradient is described in terms of biotic interactions; interactions between different organisms. This research investigates a particular biotic interaction, the lichen symbiosis, along a large environmental gradient from North to South America. Lichens are symbioses (mutually beneficial, long-term, close physical associations) between fungi and algae/cyanobacteria. Though small and often overlooked, lichens can be found in almost every terrestrial environment, making them ideal for investigating biotic interactions across large environmental gradients. This research will focus on the role of symbiosis in driving patterns of diversity, and may improve predictions of how patterns of diversity change in the face of ongoing changes in climate. This research uniquely addresses both partners in the symbiosis, and will increase our knowledge of global biodiversity through the discovery and description of new species and traits. This project will extend the research and training of a doctoral student by supporting research that moves from descriptive pattern to mechanistic process. A workshop on symbioses will be made available to undergraduate students in Michigan, and educational materials for high school classrooms will be offered via the Data Nugget program, promoting the scientific process and potentially recruiting more students to science and technology at the college level. The biotic interactions hypothesis proposes that in extra-tropical regions, abiotic selective pressures exert a stronger force, whereas in tropical regions, biotic selective pressures exert a stronger force. Furthermore, these biotic interactions lead to moving peaks of adaptation, and coevolutionary races, which further contributes to diversification in the tropics. This research investigates the dynamics of the lichen symbiosis along a latitudinal gradient by sequencing both the fungal and algal partners within five lichen-forming families of fungi found along the latitudinal gradient in order to map patterns of specificity among partners, and to test whether partner switches have resulted in diversification events or range shifts in the lichen symbiosis.