Comparison of genetic diversity and ecophysiological performance in the colony-forming polar prymnesiophyte species Phaeocystis antarctica and Phaeocystis pouchetii

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The prymnesiophyte Phaeocystis is a cosmopolitan, ecologically important and bloom-forming genus of the phytoplankton containing two colony-forming cold water species: P. pouchetii in the Arctic and P. antarctica in the Southern Ocean. Preliminary molecular biological analyses of the ribosomal RNA (rRNA) and ITS (Internal Transcribed Spacer) sequences indicated substantial inter- and intraspecific diversity, the possibility of a species complex in P. pouchetii and tried to trace the biogeographic history of P. antarctica strains in Antarctic coastal waters. Based on these results, a detailed analysis of the population structure of both polar species is intended to link genetic data to environmental para-meters as well as to ecophysiological response patterns. Microsatellites, short, repetitive sequences that are highly polymorphic, for P. antarctica were designed and successfully applied but still await statistical analysis. We will now be able to study the genetic diversity inside populations from different locations and the gene flow between them. The same approach is also planned for P. pouchetii al-though microsatellites have still to be developed if applicability tests with markers designed for P. antarctica fail.Selected clones of both Phaeocystis species with large genetic differences will be comparatively studied in terms of photosynthesis and growth under different abiotic conditions to outline the res-pective optima and tolerance limits. The main goal is to experimentally evaluate whether genetic differences are reflected in different ecophysiological response patterns which could well explain specific biogeographic distribution patterns. Moreover, this new approach offers for the first time the opportunity to relate population genetics to predicted climatic changes in both Polar Regions.