Speciation is the process by which a single species diverges into two or more descendent species. Although potential mechanisms of speciation are well known, the relative importance of different mechanisms remains poorly understood, due to the long timescales involved and the possible confounding effects of subsequent evolutionary changes and of extinction. We use analyses of evolutionary relationships and diversity patterns among present-day species to test general theories about the importance of geographical isolation and divergent selection in speciation.

Recent work is developing theoretical models of divergence under different scenarios of gene flow and recombination to determine when closure versus continuation of gene exchange occurs. The models are being applied to speciation in bacteria.

The probability of speciation on oceanic islands depends on the size of the island but also on the levels of gene flow (measured by Fst) of the organisms concerned – taxa that disperse further speciate less. Figure 4 from Kisel and Barraclough (2010).


Schmutzer, M., Barraclough, T.G. In review. The role of recombination, local versus global gene pools, and flexible genomes in the ecological speciation of bacteria.

Tang, C.Q., Obertegger, U., Fontaneto, D., Barraclough T.G. 2014. Sexual species are separated by larger genetic gaps than asexual species in rotifers. Evolution. 68: 2901-2916

Waterman R.J., Bidartondo M.I., Stofberg J., Combs J.K., Gebauer G., Savolainen V., Barraclough, T.G. and Pauw A. 2011. The effects of above and below ground mutualisms on orchid speciation and co-existence. American Naturalist. 177:E54-E68

Kisel, Y. and Barraclough T.G. 2010. Speciation has a spatial scale that depends on levels of gene flow. American Naturalist. 175:316-334.

Day, J.J., Cotton, J.A., and Barraclough T.G. 2008. Tempo and mode of diversification of Lake Tanganyika cichlid fishes. PLoS ONE, 3: e1730

Leave a Reply