|International Journal of Astrobiology (2003), 2:3:203-211 Cambridge University Press|
Copyright © 2003 Cambridge University Press
Phylogeny of Opisthokonta and the evolution of multicellularity and complexity in Fungi and Metazoa
While early eukaryotic life must have been unicellular, multicellular lifeforms evolved multiple times from protistan ancestors in diverse eukaryotic lineages. The origins of multicellularity are of special interest because they require evolutionary transitions towards increased levels of complexity. We have generated new sequence data from the nuclear large subunit ribosomal DNA gene (LSU rDNA) and the SSU rDNA gene of several unicellular opisthokont protists – a nucleariid amoeba (Nuclearia simplex) and four choanoflagellates (Codosiga gracilis, Choanoeca perplexa, Proterospongia choanojuncta and Stephanoeca diplocostata) to provide the basis for re-examining relationships among several unicellular lineages and their multicellular relatives (animals and fungi). Our data indicate that: (1) choanoflagellates are a monophyletic rather than a paraphyletic assemblage that independently gave rise to animals and fungi as suggested by some authors and (2) the nucleariid filose amoebae are the likely sister group to Fungi. We also review published information regarding the origin of multicellularity in the opisthokonts.(Received April 1 2003)
(Accepted July 10 2003)
Key Words: Choanoflagellata; Fungi; Mesomycetozoea; Metazoa; multicellularity; Nuclearia; Opisthokonta.
c1 Corresponding author.
p1 Present address: Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, CA 94598, USA. e-mail: email@example.com