Molecular phylogeny of choanoflagellates, the sister group to Metazoa

Abstract

Choanoflagellates are single-celled aquatic flagellates with a unique morphology consisting of a cell with a single flagellum surrounded by a ''collar'' of microvilli. They have long interested evolutionary biologists because of their striking resemblance to the collared cells (choanocytes) of sponges. Molecular phylogeny has confirmed a close relationship between choanoflagellates and Metazoa, and the first choanoflagellate genome sequence has recently been published. However, molecular phylogenetic studies within choanoflagellates are still extremely limited. Thus, little is known about choanoflagellate evolution or the exact nature of the relationship between choanoflagellates and Metazoa. We have sequenced four genes from a broad sampling of the morphological diversity of choanoflagellates including most species currently available in culture. Phylogenetic analyses of these sequences, alone and in combination, reject much of the traditional taxonomy of the group. The molecular data also strongly support choanoflagellate monophyly rejecting proposals that Metazoa were derived from a true choanoflagellate ancestor. Mapping of a complementary matrix of morphological and ecological traits onto the phylogeny allows a reinterpretation of choanoflagellate character evolution and predicts the nature of their last common ancestor.evolution ͉ morphology ͉ holozoa ͉ animals ͉ protists

Ancient origin of the integrin-mediated adhesion and signaling machinery

“…These findings indicate that cell adhesion and cell signaling genes might have evolved before the origin of Metazoa. Consistent with this view, choanoflagellates, the unicellular putative sister group of Metazoa (7)(8)(9)(10)(11), have been shown to possess some genes involved in cell signaling and adhesion, such as tyrosine kinases and cadherins (1,(12)(13)(14). Expressed sequence tag surveys of other unicellular relatives of metazoans, such as Capsaspora owczarzaki and Ministeria vibrans, also yielded homologs of genes involved in metazoan cell adhesion and cell signaling (9,15).…”

Sex is a ubiquitous, ancient, and inherent attribute of eukaryotic life

“…Choanoflagellates are an extremely interesting protist group, as they are the closest living relatives of multicellular animals (Metazoa) (31). They comprise some 250 described species of solitary or colonial bacterivores capturing prey with the aid of a collar of microvilli around a single posterior flagellum.…”

Exploring the evolutionary history of centrosomes

“…Among them, the most robustly predicted by phylogenetic analyses is the supergroup Opisthokonta, which comprises animals, fungi and the smaller groups Choanoflagellatea, Filasterea, Ichthyosporea and Nucleariida [44][45][46][47]. Choanoflagellates, which are unicellular or colonial free-living uniflagellates, are considered the closest living relatives of animals [45,[47][48][49][50][51]. Filasterea comprise only two known species of filose amoebae completely lacking centrioles and cilia: the free-living marine protist Ministeria vibrans and Capsaspora owczarzaki, an endosymbiont of Biomphalaria glabrata, the intermediate snail host for intestinal schistosomiasis [46,[51][52][53].…”