Evidence for widespread endemism among Antarctic micro-organisms

Understanding the enormous diversity of microbes, their multiple roles in the functioning of ecosystems, and their response to
large-scale environmental and climatic changes, are at the forefront of the international research agenda. In Antarctica, where
terrestrial and lacustrine environments are predominantly microbial realms, an active and growing community of microbial
ecologists is probing this diversity and its role in ecosystem processes. In a broader context, this work has the potential to make
a significant contribution to the long-standing debate as to whether microbes are fundamentally different from macroorganisms in
their biogeography. According to the ubiquity hypothesis, microbial community composition is not constrained by dispersal
limitation and is solely the result of species sorting along environmental gradients. However, recent work on several groups of
microalgae is challenging this view. Global analyses using morphology-based diatom inventories have demonstrated that, in
addition to environmental harshness, geographical isolation underlies the strong latitudinal gradients in local and regional diversity
in the Southern hemisphere. Increasing evidence points to a strong regionalization of diatom floras in the Antarctic and sub-
Antarctic regions, mirroring the biogeographical regions that have been recognized for macroorganisms. Likewise, the application
of molecular-phylogenetic techniques to cultured and uncultured diversity revealed a high number of Antarctic endemics
among cyanobacteria and green algae. Calibration of these phylogenies suggests that several clades have an ancient evolutionary
history within the Antarctic continent, possibly dating back to 330 Ma. These findings are in line with the current view on the origin
of Antarctic terrestrial metazoa, including springtails, chironomids and mites, with most evidence suggesting a long history of
geographic isolation on a multi-million year, even pre-Gondwana break-up timescale