Rapid evolutionary divergences in reef fishes of the family Acanthuridae (Perciformes: Teleostei) Kendall D. Clements, a, * Russell D. Gray, b and J. Howard Choat c a School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand b Department of Psychology, University of Auckland, Auckland, New Zealand c School of Marine Biology and Aquaculture, James Cook University of North Queensland, Townsville, Qld. 4811, Australia Received 3 October 2001; revised 30 May 2002 Abstract A phylogenetic analysis of the surgeonfish family Acanthuridae was conducted to investigate: (a) the pattern of divergences among outgroup and basal ingroup taxa, (b) the pattern of species divergences within acanthurid genera, (c) monophyly in the genus Acanthurus, and (d) the evolution of thick-walled stomach morphology in the genera Acanthurus and Ctenochaetus. Fragments of the 12S, 16S, t-Pro, and control region mitochondrial genes were sequenced for 21 acanthurid taxa (representing all extant genera) and four outgroup taxa. Unweighted parsimony analysis produced two optimal trees. Both of these were highly incongruent with a previous morphological phylogeny, especially with regard to the placement of the monotypic outgroups Zanclus and Luvarus. The maximum likelihood tree and the morphological phylogeny were not significantly different and the conflicting branches were very short. Split decomposition analysis identified conflict in the placement of long basal branches separated by short internodes, providing further evidence that long branch attraction is an important cause of disagreement between molecular and morphological trees. Parametric bootstrapping rejected hypotheses of monophyly of: (a) the genus Acanthurus and (b) a group containing rep- resentatives of Acanthurus/Ctenochaetus with thick-walled stomachs. The branching pattern of the likelihood and split decompo- sition trees indicates that evolution in the acanthurid clade has involved at least three periods of intense speciation. Ó 2002 Elsevier Science (USA). All rights reserved. 1. Introduction The fishes of the suborder Acanthuroidei comprise six families and approximately 125 species (Nelson, 1994) and constitute a highly characteristic and speciose group of predominantly coral reef fishes. An evaluation of trophic biology and the pattern of evolutionary diver- gence within this group is an important element in our understanding of reef trophodynamics (Choat and Cle- ments, 1998; Winterbottom and McLennan, 1993). Of particular interest is the temporal pattern of diversifi- cation of feeding patterns within clades of nominally herbivorous fishes, especially the capacity to feed on detrital aggregates (Choat and Clements, 1998). The considerable diversity of feeding modes within the acanthurids (e.g., macroscopic algal browsing, detrital feeding, and planktivory; Choat et al., 2002) provides a framework for analysing the evolution of diets in coral reef fishes (e.g., Winterbottom and McLennan, 1993). Tang et al. (1999) examined relationships within the suborder Acanthuroidei using DNA sequence data from two mitochondrial genes. Analysis of these data, which were derived from a representative species from each of the acanthuroid genera (two species in the case of Acanthurus), was compared to the results obtained from the morphological data set of Winterbottom (1993). While the DNA evidence supported the monophyly of the Acanthuroidei, it also raised three issues concerning the relationships both among and within the families that constitute the suborder. First, Tang et al. (1999) suggested that long branch attraction was a likely source of bias in their molecular phylogenetic reconstruction of this assemblage. Long branch attraction is likely to be a problem for molecular Molecular Phylogenetics and Evolution 26 (2003) 190–201 www.elsevier.com/locate/ympev MOLECULAR PHYLOGENETICS AND EVOLUTION * Corresponding author. Fax: +64-9-373-7417. E-mail address: k.clements@auckland.ac.nz (K.D. Clements). 1055-7903/02/$ - see front matter Ó 2002 Elsevier Science (USA). All rights reserved. PII:S1055-7903(02)00325-1