An environmental survey reveals hidden diversity among unicellular

The Opisthokonta clade includes Metazoa, Fungi and several unicellular lineages, such as choanoflagellates, filastereans, ichthyosporeans and nucleariids. To date, studies of the evolutionary diversity of opisthokonts have focused exclusively on metazoans, fungi and, very recently, choanoflagellates. Thus, very little is known about diversity among the filastereans, ichthyosporeans and nucleariids. To better understand the evolutionary diversity and ecology of the opisthokonts, here we analyze published environmental data from nonfungal unicellular opisthokonts and report 18S rDNA phylogenetic analyses. Our data reveal extensive diversity among all unicellular opisthokonts, except for the filastereans. We identify several clades that consist exclusively of environmental sequences, especially among ichthyosporeans and choanoflagellates. Moreover, we show that the ichthyosporeans represent a significant percentage of overall unicellular opisthokont diversity, with a greater ecological role in marine environments than previously believed. Our results provide a useful phylogenetic framework for future ecological and evolutionary studies of these poorly-known lineages. Running title: Evolutionary diversity of unicellular opisthokonts