Phylogenetic relationships among loliginid squids (Cephalopoda: Myopsida) based on analyses of multiple data sets

Abstract

The phylogenetic relationships among the loliginid squids, a species-rich group of shallow-water muscular squids, have been investigated recently using several approaches, including allozyme electrophoresis and analyses of morphological and DNA sequence data, yet no consensus has been reached. This study examines the effects of combining multiple data sets (morphology, allozymes and DNA sequence data from two mitochondrial genes) on estimates of loliginid phylogeny. Various data combinations were analysed under three maximum parsimony weighting schemes: equal weights for all characters, successive approximations and implicit weights parsimony. When feasible, support for branches within trees was assessed with nonparametric bootstrapping and decay analysis. Some ingroup relationships were consistent across all analyses, but relationships among outgroup taxa and basal ingroup taxa varied. Combining data increased bootstrap support for several nodes. Methods that downweight highly variable characters (i.e. successive approximations and implicit weights parsimony) produced very similar trees which included two major clades: a clade consisting of all species sampled from American waters (except Sepioteuthis), and a clade of several east Atlantic species (Loligo forbesi Steenstrup, Loligo vulgaris Lamarck and Loligo reynaudi d»Orbigny) plus several Indo-West Pacific species in the genera Uroteuthis and Loliolus. TheSepioteuthis species occupied a basal position within Loliginidae, but Sepioteuthis itself was not always monophyletic. The position of a clade of a few Lolliguncula species and Loligo (Alloteuthis) also varied across analyses. A new loliginid classification is proposed based on these findings.