Origin and evolutionary dynamics of Australian Elaeocarpaceae

A project undertaken at the Royal Botanic Gardens and Domain Trust, Sydney, and supervised by M. Rossetto and D. Crayn.

Background:

Australian rainforests provide a unique model for the investigation of plant evolutionary patterns. Despite representing less than 0.5 % of the total vegetation cover, it has been estimated that Australian rainforests hold up to 50 % of our terrestrial biodiversity. No other rainforest worldwide contains such a high number of rare ancient taxa, a consequence of the highly distinct evolutionary history of Australian rainforest. After 30 million years of isolation and stability, drastic climatic changes beginning approximately 15 million years ago introduced arid conditions in what was a predominantly rainforest dominated continent. These changes were further intensified during the glacial events of the Quaternary contributing to the uniqueness of our native flora.

The Elaeocarpaceae are a worldwide family of over 500 species across nine genera. Members of the family are trees or shrubs, usually found in rainforest environments. The major centres of diversity are in the Indo-Malayan and Australia-Pacific regions. Seven genera are only found in Australia if the endemic family Tremandraceae is included as suggested by recent studies and confirmed by our preliminary findings (Crayn & Rossetto 2003).

Objectives:

This project aims to investigate two broad themes on the biogeography and evolution of the Elaeocarpaceae. The first theme explores phylogenetic, biogeographic and evolutionary relationships among the Australian representatives of the family based on between-species DNA differentiation. Based on this phylogenetic framework, a second set of questions will be investigated in more detail by measuring within-species differentiation in a representative genus, Elaeocarpus.

Our main questions include:

• Can we relate genetic diversity and current geographic distribution to evolutionary origins?
• Are current ecological and evolutionary requirements limiting the distribution of Elaeocarpus in Australia, or is current distribution directly associated to the location of ancient rainforest refugia?

Answers to these questions will provide insights on how ecological traits, evolutionary potential, biogeographic origin and post-glacial survival have shaped current floristic distributions in Australian rainforests. Understanding the evolutionary basis that enabled the perseverance of taxa despite extreme environmental pressures will help us develop better conservation and management strategies for the future.

Preliminary outcomes:

Elaeocapraceae have been collected in the field in Australia and (a small number) from Papua New Guinea, a major centre of diversity of the genus Elaeocarpus. Herbarium material has also been obtained from other representative taxa and DNA extraction and experimentation has begun.

Preliminary results from over 50 taxa (including outgroups) suggest that two main lineages exist: the first comprising at least Sloanea (tropical/warm except Africa) and Aristotelia (Australia, Chile, Peru, NZ) and the second at least Crinodendron (temperate S. America), Tremandraceae (Australia), Aceratium (Australia, Malesia) and Elaeocarpus (tropical/warm except Africa). A fascinating result in view of the profound ecological differences between Tremandraceae and Elaeocarpus.

References:

Crayn, D and Rossetto M (2003) Are "Tremandraceae" a radiation within Elaeocarpaceae: molecular evidence. Presented at Australian Systematic Botany Society conference "150 Years" held at the University of Melbourne Sep 29 – Oct 3 2003.