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Speciation systems on Lord Howe Island

Lord Howe Island provides evidence in plants for the 'syngameon hypothesis' of adaptive evolution.

Howea belmoreana and H. forsteriana have evolved into separate species while growing together on Lord Howe Island (Image: W. Baker)

On Lord Howe Island, previous research has shown that in several distantly related plant genera speciation has taken place without any geographic isolation of populations (Papadopulos et al., 2011).

In a new study, published in the Journal of Evolutionary Biology (Papadopulos et al., 2013), Alex Papadopulos and colleagues from Kew, Imperial College London, the University of Sheffied and Lord Howe Island used genetic and ecological data to investigate whether or not the speciation processes in each genus were driven by divergent natural selection.

The researchers found genetic evidence of divergent selection between species, as well as further evidence of adaptation within species. Hybridisation between species still takes place in Howea and Coprosma, but the distinctiveness of the species is maintained, most likely due to selection against hybrids imposed by competition for resources.

Genetic analyses of Coprosma populations led to the discovery of a new species – a distinct hybrid population that is a putative sixth species of Coprosma to have evolved from a single ancestor that colonised the island less than 7 million years ago. This provides some of the most compelling evidence in plants for the ‘syngameon hypothesis’ – that hybridisation is an important source of genetic variation during adaptive radiations (Seehousen, 2004).

Item from Dr Bill Baker (Head of Palm Research, RBG Kew)
Kew Scientist, issue 43

Article references:

Papadopulos, A.S.T., Baker, W.J., Crayn, D., Butlin, R.K., Kynast, R.G., Hutton, I. & Savolainena, V. (2011). Speciation with gene flow on Lord Howe Island. Proceedings of the National Academy of Sciences of the United States of America 108:  13188–13193.

Papadopulos, A.S.T., Price, Z., Devaux, C., Hipperson, H., Smadja, C.M., Hutton, I., Baker, W.J., Butlin, R.K. & Savolainen, V. (2013). A comparative analysis of the mechanisms underlying speciation on Lord Howe Island. Journal of Evolutionary Biology 26: 733–745.

Seehousen, O. (2004). Hybridization and adaptive radiation. Trends in Ecology and Evolution 19: 198–207.

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