Animal Evolution Clues Drawn From Genome Sequencing, Phylogenetic Study

In Nature, researchers from the University of Vienna, the Monterey Bay Aquarium Research Institute, and elsewhere have investigated competing hypotheses in animal evolution: the notion that sponges belong to a sister group to all other animals or a scenario in which the ctenophore or comb jelly group diverged from the animal lineage first. After developing chromosome-level genomes for the Bolinopsis microptera lobate comb jelly, along with two marine sponges and three outgroup single-cell animals, the team turned to chromosome-scale gene linkage analyses to find ancestral syntenic sequence conservation in the unicellular and multicellular animals, identifying conserved features that distinguished the ctenophore and single-celled organisms from sponges and other animals. "The patterns of synteny shared by sponges, bilaterians, and cnidarians are the result of rare and irreversible chromosome fusion-and-mixing events that provide robust and unambiguous phylogenetic support for the ctenophore-sister hypothesis," the authors write. "These findings provide a new framework for resolving deep, recalcitrant phylogenetic problems and have implications for our understanding of animal evolution."