![]() microptera from the Monterey Bay, California. b, c, Specimens of species of which the genomes are reported here. ![]() These findings provide a new framework for resolving deep, recalcitrant phylogenetic problems and have implications for our understanding of animal evolution.Ī, Two alternative metazoan phylogenetic hypotheses, with either ctenophores (left) or sponges (right) as sister to all 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. Conserved syntenic characters unite sponges with bilaterians, cnidarians, and placozoans in a monophyletic clade to the exclusion of ctenophores, placing ctenophores as the sister group to all other animals. Ctenophores and unicellular eukaryotes share ancestral metazoan patterns, whereas sponges, bilaterians, and cnidarians share derived chromosomal rearrangements. We find ancient syntenies that are conserved between animals and their close unicellular relatives. We report new chromosome-scale genomes for a ctenophore and two marine sponges, and for three unicellular relatives of animals (a choanoflagellate, a filasterean amoeba and an ichthyosporean) that serve as outgroups for phylogenetic analysis. ![]() Here we develop chromosome-scale gene linkage, also known as synteny, as a phylogenetic character for resolving this question 12. Conventional phylogenetic approaches based on morphological characters and increasingly extensive gene sequence collections have not been able to definitively answer this question 7, 8, 9, 10, 11. These alternative phylogenetic hypotheses imply different scenarios for the evolution of complex neural systems and other animal-specific traits 1, 2, 3, 4, 5, 6. ![]() A central question in evolutionary biology is whether sponges or ctenophores (comb jellies) are the sister group to all other animals. ![]()
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