The timing and mode of plant diversification

Although it is clear that climatic changes can cause species extinctions, it has been far more controversial whether these changes have driven species production in tropical forests. Our work demonstrates that geologically recent climatic changes during the Ice Ages co-incide with species production in several groups of tropical rain forest herbs and trees. For example, the many species of the c. 300 in the neotropical legume tree genus Inga (300 spp.) arose during this time, and we have demonstrated similarly recent speciation of lineages in Aframomum (Zingiberaceae), Begonia and Cyrtandra (Gesneriaceae). Whilst these results cannot prove that climate changes have driven speciation, they are consistent with this idea, and contradict many animal studies that show speciation patterns to have pre-dated the Pleistocene. Over longer temporal scales we have demonstrated that diversification in wet forest restricted African Annonaceae is consistent with their responding to cycles of dry and wet climate during the last thirty million years.

Streptocarpus montigenaIn neotropical seasonally dry forests, we have investigated whether past climate changes have influenced the distribution of tree species characteristic of this biome. We are analysing large floristic inventory datasets gathered by RBGE scientists and collaborators to see if levels of floristic similarity between isolated seasonal forest areas are consistent with recent connections in times of drier climates. In collaboration with Geneva Botanical Garden, we have used molecular population genetic techniques to investigate how the distributions of two widespread South American dry forest tree species (Geoffroea spinosa and Astronium urundeuva) have been generated. In Streptocarpus, we have shown that species ranges in Africa have been heavily influenced by recent historical climate changes.

Recent phylogenetic work on the legume genus Inga has been in collaboration with the ecologists Phyllis Coley and Thomas Kursar (University of Utah, USA and Smithsonian Tropical Research Institute, Panama) who are using Inga as a model for studying the evolutionary ecology of anti-herbivory strategies in tropical plants. Inga species use two strategies to avoid herbivores: some have young leaves that expand and lignify quickly to shorten the time of vulnerability to insect herbivores, but have few chemical defences ("escape strategy"); others have young leaves that expand slowly, but have secondary chemistry that deters herbivores ("defence strategy"). Mapping these strategies onto a resolved phylogeny of Inga species suggests that the evolution of antiherbivory strategies has been associated with the remarkably rapid speciation of the genus. Our work on Inga is now supported by a BBSRC Syntax grant and a US National Science Foundation Foundations of Biodiversity grant.

Inga

Recent publications

Auvray, G., Harris, D.J., Richardson, J.E., Newman, M.F. and Särkinen, T.E. In press. Phylogeny and dating of Aframomum (Zingiberaceae). Proceedings of the 4th International Conference on the Comparative Biology of the Monocotyledons. University of Copenhagen.

Caetano, S., D. Prado, R.T. Pennington, S. Beck, A. Oliveira-Filho, R. Spichiger and Y. Naciri. (2008). The history of Seasonally Dry Tropical Forests in eastern South America: inferences from the genetic structure of the tree Astronium urundeuva (Anacardiaceae). Molecular Ecology 17:3147-3159. 

Couvreur. T.L.P., L.W. Chatrou, M.S.M. Sosef and J.E. Richardson. (2008). Molecular phylogenetics reveal multiple tertiary vicariance origins of African rain forest trees. BMC Biology 6: 54-63.

Kursar, T.A., Dexter, K.G., Lokvam, J., Pennington R.T., Richardson, J.E., Weber, M.G., Murakami, E, Drake, C., McGregor, R. & Coley, P.D. (2009). The importance of plant-herbivore interactions for diversification and coexistence in the tropical tree genus Inga. Proceedings of the National Academy of Sciences, USA. doi: 10.1073/pnas.0904786106

Hughes, M., Möller, M., Bellstedt, D.U., Edwards, T.J & de Villiers, M. (2005). Refugia, dispersal and divergence across a forest archipelago: a study of Streptocarpus in eastern South Africa. Molecular Ecology, 14: 4415-4426.

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