Deep sea isolation: Hypersaline 'islands' harbor unique life
Alexandra Stock, Virginia Edgcomb, William Orsi, Sabine Filker, Hans-Werner Breiner, Michail M Yakimov, Thorsten Stoeck. Evidence for isolated evolution of deep-sea ciliate communities through geological separation and environmental selection. BMC Microbiology, 2013

Deep in the ocean exist super salty anoxic basins that form 'islands' allowing evolution to vary between communities of ciliated plankton. These unique communities are presented in BioMed Central's open access journal BMC Microbiology, and provide an opportunity to observe multiple results of evolution from the same stock and different solutions to environmental difficulties.

About five and a half million years ago the Mediterranean sea dried up. This resulted in salty sediment, known as Messinian evaporites, in basins which were covered by sea water as the area reflooded. Salts from these basins are slowly leaching out but, since this water is denser than the surrounding sea, they are unmixable and it remains a briny column.

The ciliate plankton which live in these brines all began from the same stock, but over time have had the potential to evolve differently. Researchers from University of Kaiserslautern in collaboration with Woods Hole Oceanographic Institution, USA and CNR- Institute for Coastal Marine Environment, Italy, investigated how isolated these communities are, and whether there has been mixing between them and the surrounding ciliates in the sea.

The researchers found that there was some mixing of ciliate communities at the interfaces immediately above four different brines, and that these communities were very similar to each other. However the communities living at the heart of the brines were very different from each other even though the physical properties of each island were the same.

Dr Thorsten Stoeck who led this project said, "The isolation of these very similar habitats means that we can study alternative courses of evolution. Each of our four communities had taken a subtly different route in adapting to anoxia and hypersalinity, resulting in four very different communities. Other ancient isolated habits which also occur in the Red Sea and Gulf of Mexico may also contain 'hot spots' of as-of-yet unstudied and potentially highly divergent ecosystems."

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