Symbiotic ecology: mycobiont-photobiont interactions in tropical lichens along environmental gradients

• Applicant: Ulla Kaasalainen, Ph.D.
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems ; Evolution and Systematics of Plants and Fungi
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 408295270

Lichen symbioses are mutualistic associations between mycobionts (fungi) and photobionts (green algae and/or cyanobacteria) in which the photobionts provide carbohydrates and the fungi provide a sheltered environment for their photobionts. During their complex evolutionary history, this highly successful nutritional strategy has evolved to a plethora of different growth forms and habitat ecologies, and lichens can be found in almost all terrestrial ecosystems from the tropics to polar regions. The application of molecular biological methods has revealed previously unexpected levels of genetic diversity especially in many tropical lineages of lichen-symbiotic organisms, and while some groups of macrolichens in boreal and temperate regions are relatively well known, the knowledge about symbiont diversity and association patterns in the tropics is meagre. However, understanding the relevance of the diversity patterns and the ecology of species interactions is fundamental in addressing the challenges of environmental change to lichens. It is the aim of this project to explore how the symbiotic diversity and the complexity of interactions relate to environmental variables and define symbiont ecology. The proposal focuses on lichen symbiont interactions along a steep environmental gradient on the slopes of the tropical Mount Kilimanjaro. The study setting, previously established by the DFG funded Kilimanjaro Research group, includes 60 permanent study plots with known environmental conditions, representing 12 different ecosystems from tropical savanna to alpine heath vegetation. Lichen symbiont diversity sampled both from lichen thalli and from substrate samples on the sample plots is analyzed using molecular biological methods. Species hypotheses are constructed using a DNA barcoding approach. Nonparametric multiplicative regression (NPMR) is used to analyze differences between symbiont communities and association patterns and their correlations with environmental variables. Utilizing the established study design with unique biological material, state-of-the-art molecular methods, and thorough data analysis, I can answer several relevant and timely research questions and test predictions. My specific aims include the following. A) What is the impact of environmental stress on individual symbiont genotypes and symbiotic consortia (lichen species). B) What is the role of symbiotic interactions in determining habitat and substrate ecology. C) How does the predicted facilitative role of photobiont-mediated lichen guilds and the guild-level interactions impact lichen community structure. This project will dramatically improve our current understanding of lichen ecology and biogeography, especially mycobiont-photobiont and mycobiont-mycobiont interactions within lichen symbioses, and represent a new opening in tropical lichenology.

• DFG Programme: Research Grants