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Morphological and ecological radiation of New Zealand Pachycladon

Dr. Kim McBreen

Dr Kim McBreen

Allan Wilson Centre for Molecular Ecology and Evolution,
Institute of Molecular BioSciences
Massey University
Palmerston North
New Zealand
Email: K.S.McBreen@Massey.ac.nz
Tel: 6463569099
Fax: 6463505622

In the mid-1970’s Allan Wilson’s group suggested that a small number of regulatory genes may have been responsible for the evolution of major differences in plant form (King & Wilson 1975; Cherry, Case & Wilson 1978). These “biodiversity genes” are as yet unidentified. While the model plant Arabidopsis thaliana provides an excellent resource, it will be studies of her close relatives that are most likely to provide answers to such a question (Mitchell-Olds 2001), particularly if a closely related group has undergone a rapid radiation (Remington & Purugganan 2002). The New Zealand Pachycladon group provides just such an opportunity.

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Current estimates suggest that ancestors of Arabidopsis and the New Zealand endemic genus Pachycladon diverged ca. 10 Myr ago, and that the Pachycladon complex underwent a rapid radiation originating 1-3.5 Myr ago (Heenan et al. 2002) giving rise to 6-10 morphologically and ecologically diverse species (Heenan & Mitchell 2003). Species differ in growth habit, whether they are mono- or polycarpic, as well as in leaf and inflorescence morphology. Some are alpine, whilst others are montane and lowland. As would be expected from a close phylogenetic relationship to Arabidopsis and recent radiation, there is little molecular differentiation between species in a nuclear non-coding marker (Mitchell & Heenan 2000), and coding genes (McBreen et al. unpub. data). I am helping to investigate the potential of Pachycladon as a model system for helping to understand the genetics underlying morphological and ecological diversification in plants.