Algae World: Sellaphora

So far we have found some of the same S. pupula species in Australia as we have found in Scotland, supporting the 'everything is everywhere' idea, but we have found a greater number only in Europe or only in Australia. It’s early days and so difficult to predict what our final conclusions will be, but our results so far suggest that the biogeography of protists is more complex than some recent papers would have people believe. An intriguing finding is that in Scottish and Australian ponds that seem superficially similar (eutrophic lowland ponds, with similar floras accompanying the Sellaphoras) we find that some S. pupula species are shared, but that others are quite different. Why are some present but not others, when the conditions are apparently suitable for them? Is there really an ecological explanation (after all, every lake is unique if you measure enough variables), or are some species absent because they can't get there?

Furthermore, just because we find some of the same species in European and Australian ponds doesn’t mean that they dispersed naturally; it’s possible that humans have mediated their transfer, perhaps when stocking lakes with European fish. By studying sediment cores (belonging to Australian colleagues in Melbourne and Adelaide) that represent pre- and post-European settlement, we are hoping to determine the degree to which this human-mediated transfer may be of importance.

Lastly, using a DNA-based approach called microsatellite markers, we are assessing the degree of current gene flow between S. pupula species living in European and Australian lakes. This will provide evidence either for or against the theory of constant dispersal of diatoms. If the ubiquitous dispersal theory is correct then we would expect to find low levels of genetic differentiation between members of a species living in a pond in Edinburgh and members living in a pond in Melbourne; on the other hand if dispersal is restricted we would expect to find evidence for genetic divergence.