Patterns of lineage diversification in the genus Naso (Acanthuridae) Selma O. Klanten, a, * Lynne van Herwerden, a J. Howard Choat, a and David Blair b a Molecular Ecology and Evolution Laboratory, School of Marine Biology and Aquaculture, James Cook University, Townsville, Qld 4811, Australia b School of Tropical Biology, James Cook University, Townsville, Qld 4811, Australia Received 10 July 2003; revised 5 November 2003 Available online 17 January 2004 Abstract The evolutionary history of the reef fish genus Naso (F. Acanthuridae) was examined using a complete species-level molecular phylogeny of all recognized (19) species based on three loci (one nuclear ETS2 and two mitochondrial 16S, cyt b). This study demonstrates that distinct foraging modes and specialized body shapes arose independently at different times in the evolutionary history of the genus. Members of the subgenus Axinurus, characterized by a scombriform morphology, caudal fin structure and pelagic foraging mode, were consistently placed basal to the remaining Naso species, suggesting that pelagic foraging is plesio- morphic and benthic foraging derived in this genus. We used a genus-level phylogeny (nuclear marker, ETS2), which included several taxa from all other acanthurid genera, to obtain a range of age estimates for the most recent common ancestor of the genus Naso. These age estimates (range of 52–43.3 MY) were then used to estimate divergence times (by nonparametric rate smoothing method) of the node giving rise to extant Naso species using the combined sequence data (from all loci). The reconstruction of the pattern of divergence of extant species indicates two sequences of events. The basal species characterized by pelagic foraging modes arose during the Eocene and Oligocene. Most of the remaining Naso species, including those characterized by benthic foraging, arose over a period of 20 MY during the Miocene. Diversification during this period was associated with major plate tectonic and glaciation events, resulting in changes in sea level, ocean temperature and productivity regimes. Regardless of the foraging mode exhibited, all species of Naso have a caudal propulsive unit similar to that observed in pelagic scombriform fishes, a legacy of the basal position of the subgenus Axinurus in the phylogeny of the genus. Ó 2003 Elsevier Inc. All rights reserved. Keywords: Foraging mode; Molecular phylogeny; Acanthuridae; Fossil record; Lineage diversification; Morphology; Nonparametric rate smoothing 1. Introduction The suborder Acanthuroidei consists of six families of tropical fishes displaying a high level of structural and morphological diversity (Randall, 2002; Tyler et al., 1989; Winterbottom and McLennan, 1993). Most spe- cies are deep-bodied laterally compressed fishes with a benthic foraging mode that feed on a variety of sessile and motile invertebrates and marine plants and are strongly associated with reef environments. However, a significant minority of acanthuroid fishes display a contrasting life-style, foraging in open water for plank- tonic and small nektonic prey. The most distinctive pe- lagic foraging taxon is represented by the monotypic genus Luvarus (Family Luvaridae) confined to open waters (Tyler et al., 1989). Pelagic foraging has also been recorded from the family Acanthuridae, especially in the genera Naso and Acanthurus (Jones, 1968; Randall, 2002). The family Acanthuridae comprises 6 extant genera containing 80 species, Naso (19 recognized species), Pri- onurus (7), Paracanthurus (1), Zebrasoma (7), Acanthurus (37), and Ctenochaetus (9) (Randall, 2002). Relationships amongst the six genera are well documented from mor- phological (Winterbottom and McLennan, 1993) and molecular (Clements et al., 2003; Tang et al., 1999) stud- ies. Moreover, the morphological reconstruction of ge- neric relationships within the suborder (Winterbottom and McLennan, 1993) is congruent with the reconstruc- tion based on mitochondrial sequences (Clements et al., 2003). Two primary issues remain. First, there is a need to * Corresponding author. Fax: +61-07-4725 1570. E-mail address: Selma.Klanten@jcu.edu.au (S.O. Klanten). 1055-7903/$ - see front matter Ó 2003 Elsevier Inc. All rights reserved. doi:10.1016/j.ympev.2003.11.008 Molecular Phylogenetics and Evolution 32 (2004) 221–235 MOLECULAR PHYLOGENETICS AND EVOLUTION www.elsevier.com/locate/ympev