Phylogenetic and morphological differences of Arctic and Antarctic choanoflagellates

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Heterotrophic nanoflagellates play a very important role in marine Antarctic and Arctic ecosystems. Among these protists, choanoflagellates form a conspicuous and abundant component of the Antarctic and arctic marine nanoplankton. Although a number of quantitative and qualitative studies have been published on choanoflagellates, recent molecular biological studies of marine nanofauna indicated that morphological investigations of these tiny organisms (3-6µm cell size) reveal only limited taxonomic resolution. However, until now only about three marine choanoflagellate species have been sequenced (18S rDNA). During the proposed project will acquire cultures of nanoprotists, analyse them combining morphological and molecular biological methods and to receive information on the distribution of these highly variable protists. We would like to address the following questions: What is the molecular identity of choanoflagellates found in Artic and Antarctic waters? Do there exist Antarctic choanoflagellate species with the same 18S rDNA pattern indicating a global distribution? How variable is the 18S rDNA gene and can parts of the sequence be used to develop a method for reliable quantitative and qualitative analyses of marine choanoflagellates? Further research on choanoflagellates 1) as a sister group of metazoans would be very interesting from the viewpoint of phylogeny and 2) as a very productive group at the basis of the pelagic food web would be of special interest for a broader understanding of ecological processes in polar regions.