DNA analysis shows true dispersal o...( The embargo for this release has be...)

The embargo for this release has been changed to 7 p.m. EST Sept. 12.

In contrast to previous findings, it seems that the global distribution of macro- and microorganisms might be similar. A study in the online open access journal, BMC Evolutionary Biology, shows that some protozoa are globally dispersed, while others are geographically restricted - by looking at a new fast-evolving DNA marker. The study also reveals that the biodiversity of protozoa may be much higher than previously realised.

It has long been argued that the small size and huge populations of microorganisms aids their global dispersal. 'Everything is everywhere, but the environment selects' said Lourens Baas-Becking in 1934. Today, this Ubiquitous Dispersal Hypothesis (UDH) remains controversial compared to the alternative possibility of endemicity - the tendency of organisms to be confined to specific regions - as is found for many macro-organisms. While previous morphological and molecular analyses of environmental samples from around the world have provided evidence for UDH, these markers evolve too slowly to allow a really rigorous test of the hypothesis.

David Bass and colleagues at the University of Oxford and elsewhere, have carried out an analysis of the global distribution and diversity of three narrow taxonomic groups of cercomonads (heterotrophic flagellate protozoa) based upon PCR, cloning and sequencing of ITS1 rDNA sequences from samples gathered from around the world. ITS1 is a faster-evolving marker than the more commonly used 18S rDNA and therefore allowed the study to be done at a higher phylogenetic resolution. This approach is robust, being independent of the ability to culture or see the organism being studied.

They sequenced gene libraries of soil, freshwater, and marine cercomonads constructed from 47-80 samples per group from a wide range of habitats in locations including Panama, the Pacific, the Caribbean, Peru, UK, G
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