title: Cementing mussels to oysters in the pteriomorphian tree: a phylogenomic approach.
abstract: Mussels (Mytilida) are a group of bivalves with ancient origins and some of the most important commercial shellfish worldwide. Mytilida consists of approximately 400 species found in various littoral and deep-sea environments, and are part of the higher clade Pteriomorphia, but their exact position within the group has been unstable. The multiple adaptive radiations that occurred within Pteriomorphia have rendered phylogenetic classifications difficult and uncertainty remains regarding the relationships among most families. To address this phylogenetic uncertainty, novel transcriptomic data were generated to include all five orders of Pteriomorphia. Our results, derived from complex analyses of large datasets from 41 transcriptomes and evaluating possible pitfalls affecting phylogenetic reconstruction (matrix occupancy, heterogeneity, evolutionary rates, evolutionary models), consistently recover a well-supported phylogeny of Pteriomorphia, with the only exception of the most complete but smallest data matrix (Matrix 3: 51 genes, 90% gene occupancy). Maximum-likelihood and Bayesian mixture model analyses retrieve strong support for: (i) the monophyly of Pteriomorphia, (ii) Mytilida as a sister group to Ostreida, and (iii) Arcida as sister group to all other pteriomorphians. The basal position of Arcida is congruent with its shell microstructure (solely composed of aragonitic crystals), whereas Mytilida and Ostreida display a combination of a calcitic outer layer with an aragonitic inner layer composed of nacre tablets, the latter being secondarily lost in Ostreoidea.
authors.affiliation: Museum of Comparative Zoology, Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA sarah.lemer@gmail.com.
authors.forename: Sarah
authors.identifier: 0000-0003-0048-7296
authors.initials: S
authors.lastname: Lemer
authors.affiliation: Department of Invertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013, USA.
authors.forename: Vanessa L
authors.initials: VL
authors.lastname: González
authors.affiliation: Integrative Research Center, Field Museum of Natural History, 1400 South Lake Shore Drive, Chicago, IL 60605, USA.
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Bieler
authors.affiliation: Museum of Comparative Zoology, Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA.
authors.forename: Gonzalo
authors.initials: G
authors.lastname: Giribet
mesh_terms: D000818:Animals; D001499:Bayes Theorem; D049872:Bivalvia / Q000145:classification*; D010125:Ostreidae / Q000145:classification*; D010802:Phylogeny; D059467:Transcriptome
keywords: Bivalvia; Mollusca; evolutionary rate; genome; phylogenomics; phylogeny