Oct. 24-26, 2009, Yingjie Overseas Exchange Center, Peking University, Beijing, China中文版

The eukaryote tree: deep phylogeny and the evolution of protist body plans

Thomas Cavalier-Smith

Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS UK

Abstract

I shall discuss the deep phylogeny of protists (unicellular eukaryotes) with special reference to the results of recent multi-gene sequence trees, the evolution of protozoan body plans, and the ongoing puzzle of the location of the root of the eukaryote evolutionary tree. Eukaryotes have been divided into two major groups, the unikonts and bikonts. Unikonts primarily comprise the protozoan phyla Amoebozoa and Choanozoa, plus the kingdoms Animalia (=Metazoa) and Fungi, whereas bikonts comprise the Excavata, kingdom Plantae, chromalveolates (Alveolata plus kingdom Chromista) and Rhizaria Cerozoa plus Retaria). Recent multigene trees suggest that alveolates (i.e. Myzozoa, Ciliophora) are not sisters to Chromista, as formerly thought, but evolved from them. Rhizaria and centrohelid heliozoa may also be derived ultimately from Chromista by independent losses of the red algal chloroplast that was acquired symbiogenetically by the ancestral chromalveolate/chromist. I therefore have now transferred all three groups from the ancestral eukaryotic kingdom Protozoa to the derived kingdom Chromista. Chromista are probably sisters to Plantae, the two collectively being termed corticates, assuming that their common ancestor had cortical alveoli. Recent past ideas suggested that the eukaryote root was either between unikonts and bikonts or within the bikont excavates. I shall provide evidence that the root is actually between the traditional core excavates (Loukozoa, Percolozoa, Metamonada) and the more distinctive protozoan phylum Euglenozoa that was originally lumped with them. I therefore now formally exclude Euglenozoa from Excavata (the two groups together now being called Eozoa) and argue that a better understanding of the remarkably divergent cellular and genomic properties of Euglenozoa compared with all other eukaryotes is essential for properly appreciating early eukaryote evolution. I shall also give special attention to evidence for the monophyly and internal phylogeny of Amoebozoa and Rhizaria (especially Cercozoa and its remarkable diversity), to the paraphyly of Choanozoa, to Heliozoa, and to the relationships and special evolutionary significance of Apusozoa (Apusomonadida, Planomonadida, Mantamonadida, Micronuclearia) which appear to be unikonts not bikonts. On this new tripartite view of the eukaryote tree, Eozoa are basal and unikonts and corticates are sisters whose common ancestor evolved from them.

Thomas Cavalier-Smith

Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS UK

After first degrees at Cambridge and London Universities, and then researching algal ultrastructure and organelle development, I focused on reconstructing the history of life and deep phylogeny, understanding the origins and evolutionary diversification of bacterial and eukaryotic cells, genomes, and organelles, and the biodiversity, evolution and taxonomy of protists (unicellular eukaryotes). My laboratory has combined culturing novel protists with light and electron microscopy and extensive DNA sequencing of genes and genomes to these ends. I have described well over a hundred new species and established even more new higher taxa. My major appointments were: Lecturer and then Reader in Biophysics at University of London King’s College for 20 years; Professor of Botany at the University of Columbia, Vancouver, Canada for 10 years; NERC Professorial Research Professor in the Department of Zoology, University of Oxford for 10 years, where I am still Professor of Evolutionary Biology. I was Fellow of the Canadian Institute for Advanced Research’s Program in Evolutionary Biology for 20 years and am now on the Advisory Council of their Program in Integrated Microbial Biodiversity. I have been Guest Investigator at Rockefeller University, New York, USA and Visiting Fellow at The Australian National University, Canberra (twice) and the University of Cape Town, South Africa. I have been elected Fellow of the Royal Society of London and of the Royal Society of Canada. I received the 2004 International Prize in Biology from the Emperor of Japan, the 2007 Linnean Medal for Zoology of the Linnean Society of London, and the 2008 Frink Medal of the Zoological Society of London. I have served as President of the British Society of Protist Biology.