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What can 18S rDNA do for bivalve phylogeny?
1Institute of Zoology, University of Vienna, Althanstr.14, A-1090 Vienna, Austria.
Journal of Molecular Evolution
|July 1, 1996
Summary
Molecular data, particularly 18S rDNA sequences, offer insights into bivalve evolution. However, varying substitution rates among species complicate phylogenetic analyses and require further investigation for reliable evolutionary reconstructions.
Area of Science:
- Evolutionary Biology
- Molecular Phylogenetics
- Marine Biology
Background:
- Bivalve evolution studies benefit from molecular data, especially 18S ribosomal DNA (rDNA) sequences.
- Morphological convergences in bivalves present challenges for phylogenetic reconstruction.
- Evaluating the reliability of molecular data is crucial for understanding bivalve evolutionary history.
Purpose of the Study:
- To assess the value of 18S rDNA sequences for bivalve evolutionary studies.
- To investigate differences in molecular substitution rates among bivalve and gastropod species.
- To evaluate phylogenetic signals and tree reconstructions using various analytical methods.
Main Methods:
- Analysis of 13 complete molluscan 18S rDNA sequences (11 published, 2 new: Arca noae, Atrina pectinata).
- Comparative analysis of relative substitution rates across different taxa (Gastropoda, Eulamellibranchia, Atrina).
- Phylogenetic tree reconstructions using parsimony, neighbor-joining, and maximum-likelihood methods.
- Assessment of dataset information content via bootstrap analysis, spectral analysis, and "pattern of resolved nodes" technique.
Main Results:
- Considerable variation in 18S rDNA relative substitution rates observed, with gastropods and eulamellibranchs showing faster rates than Atrina.
- Phylogenetic analyses yielded conflicting results regarding the monophyly of Bivalvia, with Mactridae often clustering with Gastropoda.
- The position of Crassostrea was highly variable, potentially due to its rapid substitution rate.
- Atrina consistently rooted deeper than Arca, though this was not supported by spectral analysis.
- Phylogenetic signals for pectinid species were sufficient to resolve their branching pattern.
Conclusions:
- 18S rDNA sequence data hold significant potential for advancing bivalve phylogeny understanding.
- Differences in substitution rates pose a challenge, necessitating the inclusion of more sequences with comparable rates for robust phylogenetic inference.
- While a signal for Bivalvia monophyly exists, current data and analyses present a diphyletic view due to issues with Mactridae and Crassostrea placement.