Niche separation and coexistence of alpine chrysophytes

The high diversity of plankton communities has early attracted the attention of plankton ecologists and been formulated as the `Paradox of the plankton`. Relating species and species distribution with ecophysiology is still a key problem in protist ecology and distribution. This is specifically the case for chrysomonad flagellates as they are, except for a few model strains, among the most poorly known freshwater phytoplankton. Even though pigmented chrysophytes are among the dominant mixotrophs in many habitats and colourless chrysophytes are dominant in many aquatic and soil habitats including meso- to eutrophic sites, ecophysiological studies are rare. Despite some environmental surveys based on chrysophyte scales and cysts providing some links between distribution pattern and environmental factors, knowledge is still poor specifically for non-scaled chrysophytes. Thus, the ecophysiological basis for niche separation and / or coexistence are poorly understood and mainly restricted to rough assumptions. We propose to bridge this gap for chrysomonad flagellates in an alpine gradient focussing (i) on the ecophysiolopgical characterisation of the isolated strains and (ii) on a screening of 20 lakes within the alpine gradient for dominant taxa using molecular tools to finally infer the ecophysiological basis for niche separation and coexistence in chrysophytes, respectively. The main strength of the proposed project is its broadness - the link between cultivation independent environmental surveys (including morphological and molecular surveys and physical/chemical parameters) with in-depth cultivation dependent laboratory investigations, i.e. the combination of approaches which are usually separately investigated. In concert with ivestigations of chrysophyte cysts (projects FWF P 18315; CLIM-LAND) and intraspecific ecophysiological variation (project FWF P 18676) this project will therefore reveal insights into the ecophysiological basis of niche separation and coexistence of plankton taxa (i.e. in fundamental issues in plankton ecology) which can not be covered by single approaches alone. The extensive strain collection at the Institute for Limnology in Mondsee comprising recently isolated chrysophytes originating from an environmental gradient within a regionally restricted area allow to test for specific adaptations of different taxa and ecotypes of chrysomonad flagellates. The focus of our investigations will be on thermal adaptation (i.e. the probably most obvious parameter in an alpine gradient), pH adaptation (as pH is considered to be one of the most crucial parameters for chrysophyte survival strategies) and, for selected taxa, on nutritional strategies (as the chrysophytes cover different strategies from entirely phototrophic to entirely heterotrophic).

The high diversity of plankton communities has early attracted the attention of plankton ecologists and been formulated as the `Paradox of the plankton`. Relating species and species distribution with ecophysiology is still a key problem in protist ecology and distribution. The degree of generalisability of the ecology within flagellate morphospecies and flagellate phylotypes is an important objective for an ecological interpretation of cultivation- independent field surveys on flagellate diversity. We demonstrate the suitability of resting stages (stomatocysts) as a menas to differentiate cryptic protist taxa. We further demonstrate the unsuitability of current species concepts and demonstrate the historic and methodological influence on our perception of species and diversity, specifically with respect to small organisms, i.e. prostists.We show that differential seasonality of rare and abundant protist taxa explains the - so far - conflicting evidence in the `everything is everywhere` dispute. Further, the question of geographical distribution of species is strongly linked to the basic concept (definition) of species and to the importance of molecular and ecophysiological variation.