Meeting Abstract

10.1  Jan. 4  Mitochondrial genomics of sponges � Implications for animal phylogeny and evolution LAVROV, DV*; HAEN, KM; WANG, X; Iowa State University dlavrov@iastate.edu

Mitochondrial DNA of bilaterian animals is typically a small, circular-mapping molecule that encodes 37 tightly packed genes. MtDNA of choanoflagellate Monosiga brevicollis, the closest unicellular out-group of animals, is four times larger and contains 1.5 times as many genes. We are investigating this remarkable transition in mtDNA evolution, by studying mitochondrial genomes from representatives of all three classes of sponges and other groups of �lower� animals. Several intriguing funding have been made. First, we were able to show that sponge mitochondrial DNA represents an intermediate stage in the evolution of �typical� animal mtDNA. Poriferan mtDNA resembles those of other animals in its compact organization, lack of introns, and a well-conserved animal-like gene order. Yet, it contains several extra genes, encodes bacterial-like rRNA and tRNAs, and uses a minimally derived genetic code. Second, we found that the tempo and mode of mitochondrial DNA evolution are quite dissimilar among the tree major lineages of sponges. In particular, mitochondrial genomes of calcareous sponges have several unusual features that clearly set this group apart from other sponges. The diverse patterns of mitochondrial evolution in three groups of sponges suggest that different genetic architectures are hidden behind the superficially similar morphology of sponges. Third, we tested some existing hypotheses of demosponge relationships by using several different datasets derived from mitochondrial genomes: supermatrices of concatenated rRNA, tRNA and protein-coding gene sequences and gene arrangements. Our results indicate that both mitochondrial gene sequences and mitochondrial gene arrangements are informative for the study of poriferan relationships and may represent the datasets of choice for phylogenetic studies in sponges.