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Molecular and morphological evolution an choanoflagellates and the nature of their relationship to animals

ReferenceBB/C514990/1
Principal Investigator / Supervisor Professor Sandra Baldauf
Co-Investigators /
Co-Supervisors
Institution University of York
DepartmentBiology
Funding typeResearch
Value (£) 202,427
StatusCompleted
TypeResearch Grant
Start date 01/06/2005
End date 31/05/2008
Duration36 months

Abstract

A substantial body of data now indicates that choanoflagellates are the closest living relatives of animals (with the possible exception of the enigmatic taxon Ministeria vibrans). By comparing the molecular biology of choanoflagellates with that of animals, we can begin to understand the starting material from which animals and their unique multicellularity evolved. This has generated considerable interest in choanoflagellates, including one proposed and one in-progress genomic sequencing project. Two species of choanoflagellate are currently being characterised in some detail in a number of labs worldwide. However, there is almost no molecular data on any other species in the group. Choanoflagellates are single-celled aquatic heterotrophs. Their most striking feature is the presence of a collar of microvilli surrounding a single flagellum, which function together in capturing food and transporting it to the cell body. They were first identified in the 1800¿s, where their resemblance to the feeding cells (choanocytes) of sponges was soon noted. This led to the theory that choanoflagellates included the single-celled ancestors of animals. We have constructed a preliminary phylogeny of the choanoflagellates based on small subunit ribosomal RNA gene sequences. These data indicate that the group is very deep and diverse, although many of its deepest branches are not well resolved by these data. Therefore, we propose to construct a detailed molecular phylogeny of the choanoflagellates using a concatenated data set of four conservative protein-coding genes. This is because multigene data sets are now know to be generally more reliable than single genes for reconstructing deep branches. We will address four basic questions: 1) what are the major groups of choanoflagellates and how are they related to each other, 2) are choanoflagellates mono- or paraphyletic with respect to animals, ie. are they the closest living relatives or the direct ancestors of animals, 3) how did the choanoflagellate lorica, a complex basket-like structure surrounding some cells, evolve, and 4) which taxa are most suitable for genomic sequencing. We will amplify by PCR and sequence a set of four conservative protein-coding genes from cDNA prepared from 15-20 species of choanoflagellates including representatives of every proposed major division and morphological type. Culturing of taxa and nuclear characterisation will be done in Birmingham (BSCL lab) and molecular biology and phylogenetic analyses will be conducted in York (SLB lab). In collaboration with Dr Nicole King (UC Berkeley), we will also sequence our gene set from 1-2 sponges. This will help to bridge the gap between choanoflagellates and higher animals, which should increase phylogenetic accuracy (ie. decrease long branch attractions). We will also begin characterising promising candidate species (based on phylogenetic position, ease of culturing, genome size and G+C content) for genomic sequencing. This will include a collaboration with Franz Lang (Genome Canada) to characterise a random set of approximately 3000 ESTs from suitable candidate species. Joint with BB/C515312/1

Summary

unavailable
Committee Closed Committee - Genes & Developmental Biology (GDB)
Research TopicsMicrobiology
Research PriorityX – Research Priority information not available
Research Initiative X - not in an Initiative
Funding SchemeX – not Funded via a specific Funding Scheme
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