Meeting Abstract

116.7  Monday, Jan. 7  New insights into the position of the metazoan root from multi-criterion outgroup selection and microRNAs SPERLING, EA*; FEUDA, R; ROTA-STABELLI, O; ROBINSON, J; PETERSON, KJ; PISANI, D; Harvard University; NUI-Maynooth; Fondazione Edmund Mach; Dartmouth College; Dartmouth College; NUI-Maynooth sperling@fas.harvard.edu

There are several phylogenetic hypotheses relating the different sponge classes, but all agree on the same unrooted tree. Most studies place the metazoan root between the sponges and all other animals (Porifera monophyletic), or between the Silicea and all other animals, (Porifera paraphyletic). The nature of outgroup sequences can strongly affect the position of the root, especially if outgroup taxa are long-branched or compositionally-heterogeneous. Here, we conducted multi-criterion outgroup selection (Rota-Stabelli and Telford, 2008, MPE 48:103) on three different datasets. Analyses with outgroups that were ranked objectively better by the selection process, as well as analyses designed to alleviate compositional heterogeneity, found support for sponge paraphyly. Analyses with outgroups ranked worse found decreased support for sponge paraphyly or support for sponge monophyly, suggesting that sponge monophyly may be an artifact driven by compositionally-heterogeneous choanoflagellate outgroups. These results were tested by examining the presence/absence of microRNA genes, which have given insight into the phylogeny of other metazoan clades, from all major lineages of sponges. Comparison of microRNAs in calcareans and homoscleromorphs with those previously described from siliceans and eumetazoans reveals that these newly described genes are novel, with each metazoan lineage (Silicea, Calcarea, Homoscleromorpha and Eumetazoa) characterized by a non-overlapping repertoire of microRNAs. Thus while microRNAs cannot resolve between sponge mono- vs. paraphyly, these data suggest the intriguing possibility that microRNAs may have evolved multiple times independently within animals, with important implications for the evolution of gene-regulatory networks.