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Molecular Phylogenetics and Evolution Vol. 15, No. 2, May, pp. 191–214, 2000 doi:10.1006/mpev.1999.0753, available online at http://www.idealibrary.com on

Phylogeny and Historical Biogeography of the Loliginid Squids (Mollusca: Cephalopoda) Based on Mitochondrial DNA Sequence Data1
Frank E. Anderson2
Laboratory of Molecular Systematics, MRC-534, Smithsonian Institution, Washington, DC 20560Received January 5, 1999; revised August 10, 1999

INTRODUCTION
The cephalopod taxon Loliginidae (Cephalopoda: Myopsida) is a species-rich group of tropical and temperate shallow-water squids, many of which are commercial fisheries objects and neurophysiological research organisms. The worldwide distribution of these squids could make Loliginidae a useful case study in shallow-water marinebiogeography, but the phylogeny of the group is unknown. To clarify loliginid phylogeny, regions of two mitochondrial genes (the 16S rRNA and the cytochrome c oxidase subunit I genes) were sequenced for members of 19 loliginid species and several outgroups. Maximum-parsimony and maximum-likelihood analyses were performed on a combined data set, as well as on each data set individually. Analyses of thecombined data support loliginid monophyly and reveal four clades—one consisting primarily of species in American waters from two genera, one composed of 3 east Atlantic species, one consisting of the bioluminescent loliginids (Uroteuthis sensu Vecchione et al., 1998) plus Loliolus japonica, and one represented by a Loligo (Alloteuthis) subulata–Lolliguncula mercatoris pair. The likelihood of theunconstrained maximum-likelihood tree is not significantly better than the likelihoods of the best trees constrained to Sepioteuthis monophyly or Uroteuthis monophyly, but there is significant support for Lolliguncula polyphyly. Tests of alternative hypotheses of loliginid cladogenesis suggest that cladogenesis within Loliginidae is correlated with the widening of the Atlantic and the closure of theTethys Sea, although dispersal from the Indo-West Pacific is a reasonable explanation for the origin of the clade of American loliginines. 2000 Academic Press Key Words: Loliginidae; molecular systematics; maximum likelihood; squids; phylogeny.

1 This work is a portion of a doctoral dissertation submitted to the Department of Biology, University of California, Santa Cruz. 2 Current address:Department of Zoology, Southern Illinois University, Carbondale, IL 62901. E-mail: feander●su.edu.

The cephalopod taxon Loliginidae is a commercially important group of neritic squids numbering 40 to 50 described species (Brakoniecki, 1986; Nesis, 1987). Representative loliginid species occur in coastal marine waters in tropical and temperate regions around the world (Table 1) and are valuableobjects of fisheries in many areas. Loliginid squids display a diversity of morphology and body sizes. The family includes a group of large (up to 40 cm in mantle length) cuttlefish-like squids with oval-shaped fins (Sepioteuthis), smaller (typically 10–15 cm in mantle length) species with long ‘‘tails’’ at the distal tip of the mantle (Loligo [Alloteuthis]), and several species of muscular,strong-swimming squid with triangular fins (e.g., species of Loligo). In addition, several loliginid species possess paired bacterial bioluminescent organs on the ventral surface of the ink sac (Uroteuthis). The worldwide distribution of this species-rich group could make it a valuable case study for investigations of shallow-water marine biogeography and cladogenesis. Some hypotheses regarding geologicalcorrelates of cladogenesis within Loliginidae have been proposed by Brakoniecki (1986). He suggested that cladogenesis within Loliginidae has been tightly correlated with continental drift. First, he proposed that the ancestor of Sepioteuthis diverged from the rest of Loliginidae prior to the breakup of Pangaea in the Triassic. He also hypothesized that Sepioteuthis and Loligininae (all loliginids...