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Evolution of body size

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The highly venomous Australian Tiger snakes represent a well-known and extreme example of insular body size variation. We discriminate between two competing hypotheses with a molecular phylogeography data set comprising approximately 4800bp of mtDNA and demonstrate that populations of island dwarfs and giants have evolved five times independently. Moreover, these body size shifts have evolved extremely rapidly and this is reflected in the genetic divergence between island body size variants and mainland snakes. We support the hypotheses that these body size shifts are due to strong selection imposed by the size of available prey items, rather than shared evolutionary history, and our results are consistent with the notion that adaptive plasticity also has played an important role in body size shifts. The rate of body size divergence in haldanes is similar for dwarfs and giants and is in line with other studies of rapid evolution. Our data provide strong evidence for rapid and repeated morphological divergence in the wild due to similar selective pressures acting in different directions.

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