Sequence Alignment of 18 S Ribosomal RNA and the Basal Relationships of Adephagan Beetles : Evidence for Monophyly of Aquatic Families and the Placement of Trachypachidae

—Current hypotheses regarding family relationships in the suborder Adephaga (Coleoptera) are conicting. Here we report full-length 18S ribosomal RNA sequences of 39 adephagans and 13 outgroup taxa. Data analysis focused on the impact of sequence alignment on tree topology, using two principally different approaches. Tree alignments, which seek to minimize indels and substitutions on the tree in a single step, as implemented in an approximate procedure by the computer program POY, were contrasted with a more traditional procedure based on alignments followed by phylogenetic inference based on parsimony, likelihood, and distance analyses. Despite substantial differences between the procedures, phylogenetic conclusions regarding basal relationships within Adephaga and relationships between the four suborders of Coleoptera were broadly similar. The analysis weakly supports monophyly of Adephaga, with Polyphaga usually as its sister, and the two small suborders Myxophaga and Archostemata basal to them. In some analyses, however, Polyphaga was reconstructed as having arisen from within Hydradephaga. Adephaga generally split into two monophyletic groups, corresponding to the terrestrial Geadephaga and the aquatic Hydradephaga, as initially proposed by Crowson in 1955, consistent with a single colonization of the aquatic environment by adephagan ancestors and contradicting the recent proposition of three independent invasions. A monophyletic Hydradephaga is consistently, though not strongly, supported under most analyses, and a parametric bootstrapping test signiŽcantly rejects an hypothesis of nonmonophyly. The enigmatic Trachypachidae, which exhibit many similarities to aquatic forms but whose species are entirely terrestrial, were usually recovered as a basal lineage within Geadephaga. Strong evidence opposes the view that terrestrial trachypachids are related to the dytiscoid water beetles. [Adephaga; aquatic beetles; Coleoptera; sequence alignment; small subunit rRNA, tree alignment.] Adephaga contains more than 30,000 species or almost 10% of all the described species of Coleoptera and is traditionally grouped into 8 to 12 or more families. Numerous morphological characteristics indicate monophyly of the suborder (see Beutel, 1995), and several fundamental traits differ from those of the second large suborder, Polyphaga (Lawrence and Newton, 1982). Although relationships with the small suborders Archostemata and Myxophaga are still the subject of much debate, the division of the majority of extant beetle species into Adephaga and Polyphaga seems to reect a natural, deep-rooted divergence that few authors dispute (Crowson, 1960; KukalovaPeck and Lawrence, 1993; Lawrence and Newton, 1982). 4Present address: Department of Entomology, 411Science II Building, Iowa State University, Ames, Iowa 50011, USA. 5Corresponding author; E-mail: a.vogler@nhm.ac.uk Whereas Adephaga can be taken as a well-supported monophyletic group, relationships within Adephaga are highly contentious. Ecologically, they can be subdivided into a series of terrestrial groups, including Carabidae, Paussidae, Rhysodidae, Cicindelidae, and Trachypachidae (referred to as “Geadephaga”), and aquatic groups, including Gyrinidae, Dytiscidae, Noteridae, Hygrobiidae, Haliplidae, and Amphizoidae (“Hydradephaga”). This subdivision is ambiguous for the semiaquatic Amphizoidae and is compromised by the terrestrial Trachypachidae. Although trachypachids inhabit dry places away from open water and generally share the habits and body shape of the terrestrial Carabidae, they resemble Hydradephaga in several features generally considered to be adaptations to aquatic life. Further, the aquatic groups are ecologically and functionally heterogeneous and include species crawling on submerged vegetation feeding either on algae (Haliplidae) or on oligochaetes