Long-branch abstractions

Recent attention has been focused on the sensitivities of various tree reconstructing algorithms to sequence rate heterogeneity (long-branch attraction). Phylogenetic conclusions from two recent empirical studies have been indicted as artifacts attributable to long-branch attraction. Siddall et nl. (1995) concluded that Myxozoa are cnidarians and sister group to Polypodium based on 18S rDNA and morphology. Hanelt et nl. (1996) argued that this result is due to long-branch attraction. Whiting et al. (1997) concluded that the Strepsiptera are sister group to Diptera based on parsimony analysis of 18S rDNA, 28S rDNA, and morphology. Huelsenbeck (1997) argued that this result also is attributable to long-branch attraction. We demonstrate that the analyses and arguments dismissing these results as the effects of long-branch attraction are fundamentally flawed. The criteria employed by these authors were applied arbitrarily by them to the groups that they did not want, and yet using those same criteria, there is more reason to exclude other taxa besides Polypodium and there is more reason to disbelieve monophyly of Diptera than monophyly of Strepsiptera with Diptera. Moreover, it is asserted, long-branch attraction cannot explain the presence of nematocysts in Myxozoa and halteres in Strepsiptera. For these reasons, and in light of the demonstration that long branches cannot attract each other in their mutual absence, we conclude that the monophyly of Myxozoa + Polypodium and Strepsiptera + Diptera is not due to long-branch attraction. We suggest that maximum likelihood methods are extremely sensitive to taxon and character sampling and that these data sets are demonstrative of the long-branch repulsion problem. (C) 1999 The Willi Hennig Society.