Journal Article

Resolving the evolutionary relationships of molluscs with phylogenomic tools

Dunn, Casey W., Wilson, Nerida G., Rouse, Greg W., Goetz, Freya E., Feehery, Caitlin, Andrade, Sónia C. S., Smith, Stephen A., Giribet, Gonzalo

2011

Overview

Molluscs get together Phylogenomic methods are beginning to resolve one of the more tricky issues facing evolutionary biologists — making sense of the complicated interrelationships of the Mollusca. Casey Dunn and colleagues have managed to recover information from the crucial but hard-to-get-at Monoplacophora, a primitive group of deep-sea molluscs, revealing a shared ancestry with cephalopods. Together with the recent paper by Kocot et al . ( http://go.nature.com/g9trkt ), this study shows that the bivalves and gastropods form a single group. Molluscs (snails, octopuses, clams and their relatives) have a great disparity of body plans and, among the animals, only arthropods surpass them in species number. This diversity has made Mollusca one of the best-studied groups of animals, yet their evolutionary relationships remain poorly resolved 1 . Open questions have important implications for the origin of Mollusca and for morphological evolution within the group. These questions include whether the shell-less, vermiform aplacophoran molluscs diverged before the origin of the shelled molluscs (Conchifera) 2 , 3 , 4 or lost their shells secondarily. Monoplacophorans were not included in molecular studies until recently 5 , 6 , when it was proposed that they constitute a clade named Serialia together with Polyplacophora (chitons), reflecting the serial repetition of body organs in both groups 5 . Attempts to understand the early evolution of molluscs become even more complex when considering the large diversity of Cambrian fossils. These can have multiple dorsal shell plates and sclerites 7 , 8 , 9 , 10 or can be shell-less but with a typical molluscan radula and serially repeated gills 11 . To better resolve the relationships among molluscs, we generated transcriptome data for 15 species that, in combination with existing data, represent for the first time all major molluscan groups. We analysed multiple data sets containing up to 216,402 sites and 1,185 gene regions using multiple models and methods. Our results support the clade Aculifera, containing the three molluscan groups with spicules but without true shells, and they support the monophyly of Conchifera. Monoplacophora is not the sister group to other Conchifera but to Cephalopoda. Strong support is found for a clade that comprises Scaphopoda (tusk shells), Gastropoda and Bivalvia, with most analyses placing Scaphopoda and Gastropoda as sister groups. This well-resolved tree will constitute a framework for further studies of mollusc evolution, development and anatomy.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 631/208/182 / 631/208/212/2306 / 631/601 / Analysis / Animals / Biological and medical sciences / Biological evolution / Bivalvia - classification / Bivalvia - genetics / Cambrian / Cephalopoda - classification / Cephalopoda - genetics / Evolution / Flowers & plants / Fossils / Fundamental and applied biological sciences. Psychology / Gastropoda - classification / Gastropoda - genetics / Gene Expression Profiling / Genetic aspects / Genetics / Genetics of eukaryotes. Biological and molecular evolution / Humanities and Social Sciences / Identification and classification / Invertebrates / letter / Likelihood Functions / Methods / Models, Biological / Mollusca / Mollusca - classification / Mollusca - genetics / Mollusks / multidisciplinary / Natural history / Origin / Phylogenetics / Phylogeny / Physiological aspects / Science / Species diversity / Species Specificity / Systematics. Geographical distribution / Transcriptome - genetics