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

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
 
Final Report Year 2022

Final Report Abstract

Lichen symbioses are mutualistic associations between mycobionts (lichenized fungi) and photobionts (green algae and/or cyanobacteria) and they can be found in almost all terrestrial ecosystems from the tropical to polar regions. While some groups of lichens in boreal and temperate regions are relatively well known, our knowledge of tropical and African lichens, their interactions and symbiont diversity is meagre. This project focused on lichen symbioses in several East African mountain areas, utilizing especially the environmental gradients on the slope of Mt. Kilimanjaro in Tanzania and the montane forest of the nearby Taita Hills in Kenya. The mycobionts and photobionts were identified using commonly used genetic markers. As a result, a much higher species diversity was revealed than expected and previously known from this area. In genus Leptogium, for example, approximately 60 new species seem to exist in the area, and many of the traditionally considered morphological species were shown to contain several unrelated lineages. In the genus Peltigera, a new species (P. alkalicola) was described from the alpine zone of Mt. Kilimanjaro, and also several other genera contain new species. The observed interaction networks of lichen communities are complex, with most mycobiont species commonly sharing photobionts with other species, forming photobiont-mediated lichen guilds. Interestingly, also a structural difference was detected between two guilds probably reflecting differences in the ecological characteristics of the two main groups of cyanobacterial photobionts. I believe that these guilds are an integral part of lichen ecology even globally, possibly facilitating establishment and adaptation within new and marginal habitats, thus driving evolutionary diversification. Early succession of epiphytic communities in montane forests was also observed: In moist forests, liverworts and macrolichens formed diverse communities, and precipitation from fog was shown to be important especially for the establishment of many macrolichens. In contrast, under drier conditions, the early communities were comprised of crustose lichens and green algae. Mosses were virtually absent from all of the early communities, even though moss species were often abundant in the surroundings. An initially unexpected addition to the project at geologic time scale was the discovery of the first African lichen fossil from Miocene Ethiopian amber. In general, the project has produced a substantial amount of new morphologic, genetic and ecological data from a global biodiversity hotspot in tropical East Africa. These data help filling the existing tropical biodiversity data gap which is especially severe in Africa.

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