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Along Came a Spider

Credit: Nick Birks, Wildflight Australia Photography

Credit: Nick Birks, Wildflight Australia Photography

By Sophie Harrison

Genetic studies reveal that trapdoor spiders colonised Kangaroo Island after surviving a remarkable rafting journey from South Africa.

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Spiders are not normally associated with oceanic voyages. Indeed, for much of the Southern Hemisphere’s flora and fauna – including that of Australia – it seems more likely that the current distributions of many species are a result of their presence on the ancient supercontinent Gondwana rather than by any remarkable feats of dispersal. When Gondwana broke into the land masses that are now known as Antarctica, South America, Africa, Madagascar, India and Australia, species that were already living on the supercontinent were taken with it – physically “inherited” at the point of separation.

Therefore, when we see related groups of organisms with poor dispersal ability living on these land masses, we assume in the first instance that their distributions are related to shifting continents rather than shifting organisms. Such distribution patterns are called “vicariant”.

However, advances in genetic techniques mean we can now investigate the evolutionary relationship between species and the timing of their separation, and make more robust inferences about their evolutionary history. In essence, we can use genetic similarity to calculate how closely related species and populations are to each other. As DNA usually mutates at fairly constant rates, these rates can be used to calculate when two taxa may have diverged, and therefore determine if this timing...

The full text of this article can be purchased from Informit.