Strain diversification and species diversification: Attempts to understand microbial
Dept of Biology, Research group for Marine Microbiology, Univ. of Bergen, Norway.
Since the realization of high abundance and activity of viruses in natural aquatic systems 25 years ago, it has been assumed that viruses play an important role in regulating microbial biodiversity and in shunting material out of the food chain transport towards higher trophic levels, sending it back towards the dissolved pool. Models of these processes thus contain direct links between biodiversity and ecosystem function. Obtaining conclusive evidence supporting or refuting these models has, however, proven difficult. A problem may be that most of the experimental work has assumed the models' "host-groups" to correspond to species, and thus to correspond to data obtained from 16s rDNA sequencing. It is clear, however, that the old idea of clonal species populations in natural communities is wrong; a species is more like a collection of strains with large between-strain variations in parts of their DNA. This is what one would expect from host-virus evolutionary arms races observable in laboratory systems. Assuming viruses to be strain-, rather than species-specific gives models where there is a predator control on community size and a virus control on strain size, but no explicit top-down control of species size. The consequences of this for the biodiversity-ecosystem functioning relationships is discussed.