Meeting Abstract
Hox genes control patterning of body regions along the bilaterian anterior-posterior axis and are found in cnidarians, making them good targets for better understanding evolution of axial patterning in animals. The relationships between cnidarian and bilaterian Hox genes remain unclear, possibly because previous research has focused on limited cnidarian taxa Here, we present a phylogeny of Hox and related homeobox genes using the broadest cnidarian sampling to date, including representatives from Octocorallia and Hexacorallia as well as all four medusozoan groups, Hydrozoa, Scyphozoa, Staurozoa, and Cubozoa. One notable result is the phylogenetic placement of genes known in the anthozoan Nematostella vectensis to be involved in specifying the directive axis, a secondary body axis perpendicular to the primary cnidarian oral-aboral axis. Phylogenetic placement suggests the directive axis genes were lost in medusozoans, potentially as an adaptation to pelagic open-ocean life. Overall, our results are consistent with a scenario of significant Hox gene loss in both cnidarians and bilaterians.
