Meeting Abstract
The position of ctenophores and sponges on the tree of life is among the most contentious issues in biology. Historically, based on morphology and cell types, sponges were thought to be the sister group to all other animals while ctenophores, cnidarians, and bilaterians were believed to form a monophyletic clade. Early molecular phylogenies based on a small number of genes (e.g. 18S and COI) supported the former but placed Placozoa as the sister group to Cnidaria and Bilateria. Beginning with a landmark study in 2008 by Dunn and colleagues, the majority of animal phylogenomic analyses have recovered Ctenophora as the sister group to the rest of animals. To test whether these phylogenomic results are spurious or reflect true relationships, we have applied gene content as a phylogenetic marker. In addition to being largely independent from sequence-based alignments, gene-content phylogenies provide reduced effects of unequal rates of evolution and fewer ambiguous signals than sequence data. Like sequence-based phylogenomics, gene-content analyses afford large datasets (>20,000 characters) and objective and repeatable matrix construction. In the current study we augment the gene content matrix from Ryan et al. (2013) with a substantial amount of new data from several ctenophore, sponge, and outgroup species in an attempt to robustly solve the relationships between the major animal lineages.
