Sympatric Speciation in Palms: Howea on Lord Howe Island
A collaborative team led from Kew has demonstrated that the two species of Howea, a palm genus endemic to Lord Howe Island (Howea forsteriana pictured here), have speciated sympatrically. The case study joins a small number of examples that indicate that sympatric speciation is actually possible. © Bill Baker
The origin of species diversity has challenged biologists for over two centuries. Allopatric speciation, species divergence resulting from geographical isolation, is well documented. However, sympatric speciation, divergence without geographical isolation, is highly controversial. Claims of sympatric speciation must demonstrate species sympatry, sister relationships, reproductive isolation, and that an earlier allopatric phase is highly unlikely; no empirical study has convincingly satisfied all criteria.
From the first phase of this project, funded by the Leverhulme Trust (2003-2005), we have published results in Nature (Savolainen et al. 2006) which provide clear support for sympatric speciation in a case study of two species of palm on an oceanic island. A large dated phylogenetic tree shows that the two species of Howea (Arecaceae), endemic to the remote Lord Howe Island (LHI), are sister taxa and diverged from each other well after the island was formed 6.9 million years ago. During extensive fieldwork, we found a substantial disjunction in flowering time that is correlated with soil preference. In addition, a genome scan (AFLP) indicates that only few genetic loci are more divergent between the two species than expected under neutrality, a finding consistent with models of sympatric speciation involving disruptive/divergent selection. This unique case study of sympatric speciation in plants provides a tantalizing opportunity for refining theoretical models on the origin of species and new impetus for exploring putative plant and animal examples on oceanic islands.
Project Team
Project Leader: Savolainen, Vincent
Herbarium
William Baker
Jodrell Laboratory
James Clarkson, Christian Lexer , Martyn Powell, Vincent Savolainen, David Springate
Project Partners and Collaborators
Australia
Ian Hutton (Independent botanist)
Denmark
University of Aarhus
France
Centre d’Ecologie Fonctionelle et Evolutive, Montpellier
Switzerland
University of Lausanne
Funders
UK
Leverhulme Trust
Annex Material
Savolainen, V., Anstett, M.-C., Lexer, L., Hutton, I, Clarkson, J.J, Norup, M.V., Powell, M.P., Springate, D., Salamin, N. & Baker, W.J. 2006. Sympatric Speciation in Palms on an Oceanic Island. Nature doi:10.1038/nature04566.