What can 18S rDNA do for bivalve phylogeny? |
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Authors: | Gerhard Steiner Manfred Müller |
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Institution: | (1) Institute of Zoology, University of Vienna, Althanstr. 14, A-1090 Vienna, Austria;(2) Institute of Genetics, University of Vienna, Dr.Bohrgasse 1, A-1030 Vienna, Austria |
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Abstract: | Molecular characteristics, especially 18S rDNA sequences, may be of great value for the study of bivalve evolution and its
numerous morphological convergencies once the reliability of these data can be evaluated. The analysis of 11 published complete
molluscan sequences and two new ones,Arca noae andAtrina pectinata, reveals considerable differences in relative substitution rates. The gastropod and eulamellibranch species have the fastest
and Atrina species have the slowest rates. Two methods are used to assess the information contents of the dataset in addition
to bootstrap analysis, spectral analysis, and the “pattern of resolved nodes” technique. Tree reconstructions by parsimony,
neighbor-joining, and maximum-likelihood differ in regard to the position of the eulamellibranch family Mactridae and ofCrassostrea. Although there is a signal for the monophyly of Bivalvia, Mactridae cluster with Gastropoda in most runs, rendering Bivalvia
diphyletic. The position ofCrassostrea was extremely variable, probably due to the high substitution rate of this species.Atrina roots deeper thanArca in all trees, although a corresponding signal in spectral analysis is absent. Phylogenetic signals among the three pectinid
species are low but sufficient to resolve the branching pattern. The tree inferred from the 18S rDNA and from morphological
data has Bivalvia monophyletic with a basal polytomy of Mactridae,Crassostrea, and the remaining Pteriomorphia, whereArca branches off before Atrina and the Pectinidae.Argopecten is sister group to the other two pectinids; 18S sequence data will have great impact on our understanding of bivalve phylogeny,
but only when more sequences of similar substitution rates are available.
Correspondence to: G. Steiner |
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Keywords: | Mollusca Bivalvia Phylogeny 18S rDNA Spectral analysis Atrina pectinata Arca noae |
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