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Symbionts and changing environment: Lichen diversity and photobiont associations in tropical mountain ecosystems

Periodic Reporting for period 2 - Tropical lichens (Symbionts and changing environment: Lichen diversity and photobiont associations in tropical mountain ecosystems)

Reporting period: 2017-09-01 to 2018-08-31

Lichen symbioses are stable mutualistic associations in which eukaryotic algae and/or cyanobacteria provide carbohydrates for heterotrophic fungi. This represents a highly successful nutritional strategy, which allows symbiotic organisms to greatly expand their ecological ranges. During their diverse evolutionary history lichen symbioses have evolved a plethora of different growth forms and habitat ecologies, and today lichens are found in most terrestrial ecosystems from the tropics to polar regions. Generally, lichen fungi (mycobionts) are highly selective toward their phototrophic symbionts (photobionts).
The application of modern molecular methods to lichen systematics has recently revealed unprecedented levels of genetic diversity in many lineages of lichen-symbiotic organisms. While some groups of boreal and temperate macrolichens are relatively well known, very little is still known about tropical lineages and hundreds of new lichen species have recently been identified from the Neotropics alone. Our knowledge of African lichens is particularly poor and mainly comes from the pre-molecular era. The DNA-based methods have clearly shown that many traditional species concepts and nomenclature need critical updating and revision, but such methods have so far only been applied to very few lichen specimens collected from scattered locations within tropical Africa.
The specific research objectives of this project are 1) to provide the first account of lichen symbiont diversity in tropical mountains, including surveys (a) of remnant forest patches in a global biodiversity hot spot and (b) along a steep natural climatic gradient on the slopes of a high tropical volcano; and 2) to elucidate the effects of human induced environmental change to lichen symbiotic organisms, including the effects of (a) dwindling and fragmentation of indigenous forests, (b) expansion of agricultural and other disturbed ecosystems, and (c) changing climate studied along a naturally existing gradient.
The study areas of this project are located in tropical mountains of Kenya and Tanzania. Taita Hills in southeast Kenya is part of a well-known biodiversity hotspot and home to a high diversity of endemic species, while the more recently formed dormant volcano Mt. Kilimanjaro in the northeast Tanzania provides pronounced altitudinal zonation of vegetation on its slopes. Currently these African montane forests are threatened by human activities, including land clearing, firewood collection, introduction of foreign species, and recently also the effects of climate change. Still the remaining cloud forests function as ‘natural water towers’ for the semiarid plains around the mountains, and also epiphytic lichens play their own role in maintaining this ecosystem service.
The practical work during the reporting period towards achieving the objectives includes systematic sampling of various study plots in indigenous forest fragments and tree plantations in Taita Hills, Kenya, and of 65 study plots situated along five altitudinal gradients reaching from savanna to alpine Helichrysum heaths and including the several natural and disturbed ecosystems on the slope of Mt. Kilimanjaro, Tanzania. Additionally, material collected along four altitudinal transects on the slopes of Mt. Kasigau, Kenya, has been obtained.
Approximately 2700 specimens have been microscopically and micro-chemically studied and tentatively identified, and DNA sequences from several fungal and cyanobacterial markers have been produced from over 700 specimens. Phylogenetic analyses have been performed for several fungal groups, revealing many new species. Photobiont mediated cyanolichen guilds present in the forest fragments of the Taita Hills have been delimited and their interactions analyzed. Analyses have also revealed very clear correlation between lichen symbiont diversity and composition and environmental variables.
The results have been disseminated via several scientific publications, either already published, in review, or in preparation. Additionally, a popularized article has been submitted and will be published in the beginning of 2019. The results have also been presented in several scientific meetings, including for example the AfroMont: Global research network for African mountains conference and the XXI AETFAT Congress: Systematics, biogeography and conservation of African plants and fungi.
Our results provide significant accumulation of knowledge about the lichen symbiont diversity in the tropics, including knowledge of an abundance of new species. The project provides information on the effects of environmental variables to symbiotic organisms, which is crucial for example for biodiversity conservation, applicable also to other tropical montane forest ecosystems, and advance our understanding of the lichen symbiosis as a whole.
A new genus of lichenicolous fungi from Mt. Vuria in Taita Hills, Kenya, described in this project