Disentangling the evolutionary history and biogeography of the diatoms in the polar regions: data from fossils and molecular phylogenies

Because of their immense diversity, the systematics of protists, and diatoms in particular, is complex and challenging. Since species taxonomy has far-reaching consequences for our understanding of diatom evolutionary history, ecology and biogeography, detailed studies into species limits and diversity are needed if we are to advance our understanding of the range dynamics and diversification of diatoms. However, the biogeography and ecology of (pseudocryptic) diatom species is highly understudied and there are virtually no data available on the timing of lineage splitting within species complexes, especially for the Polar Regions. Furthermore, community based studies on higher taxonomic levels are increasingly showing that diatoms show biogeographical patterns in space and time and indicate that the Arctic and Antarctic regions show marked differences in their diatom floras. In the present study, we used a combination of (i) Miocene fossil diatom assemblages from the Antarctic continent, and (ii) phylogeographic data of the semiterrestrial diatom complex Pinnularia borealis Ehrenberg as a case study for speciation, evolutionary history and biogeography of diatoms in the Polar Regions