Meeting Abstract

P1.67  Friday, Jan. 4  Illuminating the Biology of the Common Unicellular Ancestor of Animals and Choanoflagellates FOZOUNI, P.*; RICHTER, D.J.; KING, N. ; Univ. of California, Berkeley; Univ. of California, Berkeley; Univ. of California, Berkeley pfozouni@berkeley.edu

All animals share a common unicellular ancestor that gave rise to the present diversity of animal forms. To better understand animal origins, we study choanoflagellates, the closest living relatives of animals. We hypothesize that genes shared exclusively between choanoflagellates and animals are likely to have played key roles in animal evolution, and we use sequencing as a tool to discover these genes. Only two of the twenty-one choanoflagellate species currently in culture have sequenced genomes: Monosiga brevicollis and Salpingoeca rosetta. These two genomes contain a diversity of gene families that were previously thought to have been animal-specific. However, M. brevicollis and S. rosetta are closely related within the phylogenetic tree of choanoflagellates, and thus shared gene loss in their common ancestor could lead to an underestimate of the true complexity of the ancestor of choanoflagellates and animals. To address this, we sequenced the transcriptomes of the remaining nineteen choanoflagellate species in culture. Using these data, we have reconstructed a substantially more complete estimate of the genomic complexity of the common unicellular ancestor of choanoflagellates and animals, including a marked increase in the number of genes we identify as exclusively shared between animals and choanoflagellates. Among these are a number of key gene families involved in diverse aspects of animal development and signaling, which we hypothesize were likely to have played roles in animal evolution. We will present several notable examples and discuss their implications for animal evolution.