Congruence of Morphological and Molecular Phylogenies
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When phylogenetic trees constructed from morphological and molecular evidence disagree (i.e. are incongruent) it has been suggested that the differences are spurious or that the molecular results should be preferred a priori. Comparing trees can increase confidence (congruence), or demonstrate that at least one tree is incorrect (incongruence). Statistical analyses of 181 molecular and 49 morphological trees shows that incongruence is greater between than within the morphological and molecular partitions, and this difference is significant for the molecular partition. Because the level of incongruence between a pair of trees gives a minimum bound on how much error is present in the two trees, our results indicate that the level of error may be underestimated by congruence within partitions. Thus comparisons between morphological and molecular trees are particularly useful for detecting this incongruence (spurious or otherwise). Molecular trees have higher average congruence than morphological trees, but the difference is not significant, and both within- and between-partition incongruence is much lower than expected by chance alone. Our results suggest that both molecular and morphological trees are, in general, useful approximations of a common underlying phylogeny and thus, when molecules and morphology clash, molecular phylogenies should not be considered more reliable a priori.
KeywordsCongruence Morphology Molecules Phylogenetic accuracy Tree distance metrics
This work was partially funded by a Leverhulme Trust grant to MJB, and by a BBSRC grant 40/G18385, and an NHM-MRF award to MW. DP was supported by a Marie Curie Intra European Individual Fellowship (MEIF-CT-2005-010022). We would like to thank Anthony Bledsoe, Andy Purvis and Clive Moncrieff for the useful advice on statistical data analyses, and Richard Olmstead and two anonymous reviewers for their helpful and insightful comments.
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