Investigating the Bivalve Tree of Life -- an exemplar-based approach combining molecular and novel morphological characters.

Bieler, Rüdiger and Mikkelsen, Paula M. and Collins, Timothy M. and Glover, Emily A. and González, Vanessa L. and Graf, D. L. and Harper, E. M. and Healy, J. and Kawauchi, Gisele Y. and Sharma, Prashant P. and Staubach, S. and Strong, E. E. and Taylor, John D. and Temkin, I. and Zardus, J. D. and Clark, S. and Guzmán, Alejandra and McIntyre, E. and Sharp, P. and Giribet, Gonzalo (2014) Investigating the Bivalve Tree of Life -- an exemplar-based approach combining molecular and novel morphological characters. Invertebrate Systematics, 28 (1). pp. 32-115. ISSN 1445-5226, ESSN: 1447-2600 DOI

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To re-evaluate the relationships of the major bivalve lineages, we amassed detailed morpho-anatomical, ultrastructural and molecular sequence data for a targeted selection of exemplar bivalves spanning the phylogenetic diversity of the class. We included molecular data for 103 bivalve species (up to five markers) and also analysed a subset of taxa with four additional nuclear protein-encoding genes. Novel as well as historically employed morphological characters were explored, and we systematically disassembled widely used descriptors such as gill and stomach ‘types’. Phylogenetic analyses, conducted using parsimony direct optimisation and probabilistic methods on static alignments (maximum likelihood and Bayesian inference) of the molecular data, both alone and in combination with morphological characters, offer a robust test of bivalve relationships. A calibrated phylogeny also provided insights into the tempo of bivalve evolution. Finally, an analysis of the informativeness of morphological characters showed that sperm ultrastructure characters are among the best morphological features to diagnose bivalve clades, followed by characters of the shell, including its microstructure. Our study found support for monophyly of most broadly recognised higher bivalve taxa, although support was not uniform for Protobranchia. However, monophyly of the bivalves with protobranchiate gills was the best-supported hypothesis with incremental morphological and/or molecular sequence data. Autobranchia, Pteriomorphia, Heteroconchia, Palaeoheterodonta, Archiheterodonta, Euheterodonta, Anomalodesmata and Imparidentia new clade ( = Euheterodonta excluding Anomalodesmata) were recovered across analyses, irrespective of data treatment or analytical framework. Another clade supported by our analyses but not formally recognised in the literature includes Palaeoheterodonta and Archiheterodonta, which emerged under multiple analytical conditions. The origin and diversification of each of these major clades is Cambrian or Ordovician, except for Archiheterodonta, which diverged from Palaeoheterodonta during the Cambrian, but diversified during the Mesozoic. Although the radiation of some lineages was shifted towards the Palaeozoic (Pteriomorphia, Anomalodesmata), or presented a gap between origin and diversification (Archiheterodonta, Unionida), Imparidentia showed steady diversification through the Palaeozoic and Mesozoic. Finally, a classification system with six major monophyletic lineages is proposed to comprise modern Bivalvia: Protobranchia, Pteriomorphia, Palaeoheterodonta, Archiheterodonta, Anomalodesmata and Imparidentia.

Item Type: Article
Additional Information: This paper is open access and available in its entirety from the journal web site, use the doi or url links.
Uncontrolled Keywords: 2014AREP; IA67;
Subjects: 04 - Palaeobiology
Divisions: 04 - Palaeobiology
07 - Gold Open Access
Journal or Publication Title: Invertebrate Systematics
Volume: 28
Page Range: pp. 32-115
Identification Number:
Depositing User: Sarah Humbert
Date Deposited: 14 Feb 2014 18:58
Last Modified: 13 Jul 2014 17:32

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