Genome skimming elucidates the evolutionary history of Octopoda

Phylogenies for Octopoda have, until now, been based on morphological characters or a few genes. Here we provide the complete mitogenomes and the nuclear 18S and 28S ribosomal genes of twenty Octopoda specimens, comprising 18 species of Cirrata and Incirrata, representing 13 genera and all five putative families of Cirrata (Cirroctopodidae, Cirroteuthidae, Grimpoteuthidae, Opisthoteuthidae and Stauroteuthidae) and six families of Incirrata (Amphitretidae, Argonautidae, Bathypolypodidae, Eledonidae, Enteroctopodidae, and Megaleledonidae) which were assembled using genome skimming. Phylogenetic trees were built using Maximum Likelihood and Bayesian Inference with several alignment matrices. All mitochondrial genomes had the ‘typical’ genome composition and gene order previously reported for octopodiforms, except Bathypolypus ergasticus, which appears to lack ND5, two tRNA genes that flank ND5 and two other tRNA genes. Argonautoidea was revealed as sister to Octopodidae by the mitochondrial protein-coding gene dataset, however, it was recovered as sister to all other incirrate octopods with strong support in an analysis using nuclear rRNA genes. Within Cirrata, our study supports two existing classifications suggesting neither is likely in conflict with the true evolutionary history of the suborder. Genome skimming is useful in the analysis of phylogenetic relationships within Octopoda; inclusion of both mitochondrial and nuclear data may be key

A redescription of the fossil coleoid cephalopod genus Palaeololigo Naef, 1921 (Decapodiformes: Palaeololiginidae) and its relationship to Recent squids

Neocoleoid cephalopods are poorly represented in the fossil record and fossils which can be confidently aligned with extant species are very scarce. The rare Solnhofen genus Palaeololigo is an exception to this, showing marked resemblance to Recent squids. Naef misinterpreted the structure of the fossilized gladius of Palaeololigo and the present study redescribes the genus. The gladius and fossilized fin impressions of Palaeololigo closely resemble that of the extant decapodiform squid genera Bathyteuthis and Chtenopteryx (Superfamily Bathyteuthoidea). The possible relationship between Palaeololigo and the bathyteuthoids and their position in decapodiform phylogenetics is discussed

A redescription of the fossil coleoid cephalopod genus Palaeololigo Naef, 1921 (Decapodiformes: Palaeololiginidae) and its relationship to Recent squids

Neocoleoid cephalopods are poorly represented in the fossil record and fossils which can be confidently aligned with extant species are very scarce. The rare Solnhofen genus Palaeololigo is an exception to this, showing marked resemblance to Recent squids. Naef misinterpreted the structure of the fossilized gladius of Palaeololigo and the present study redescribes the genus. The gladius and fossilized fin impressions of Palaeololigo closely resemble that of the extant decapodiform squid genera Bathyteuthis and Chtenopteryx (Superfamily Bathyteuthoidea). The possible relationship between Palaeololigo and the bathyteuthoids and their position in decapodiform phylogenetics is discussed

Evolution of the Antarctic marine fauna: what can DNA and fossils tell us?

The opening of the Drake Passage, establishment of the Polar Front and the onset of cooling around the Eocene-Oligocene boundary have been recognised as the most significant events in shaping the recent Antarctic marine fauna. Glacial cycles leading to loss of shelf habitat during glaciations may have been integral in determining extant biodiversity, including the establishment of regional isolation and diversification. Adaptive radiation of major clades, notably icefish, molluscs and crustaceans, occurred in isolation from the rest of the world. Cooler periods may have been associated with extinction of cold-intolerant species but rapid evolution of cold-tolerant groups. These groups have radiated and there is evidence that some have invaded other parts of the world. Modern techniques utilising DNA, fossil and biogeographical evidence can be used to give robust estimates to determine the dates of divergence and molecular rate. This sheds light onto the evolutionary history of the Antarctic marine fauna

Molecular evolutionary relationships of the octopodid genus Thaumeledone (Cephalopoda: Octopodidae) from the Southern Ocean

Recent trawling in the Southern Ocean has yielded individuals of a number of species of the deep sea octopod genus Thaumeledone. This paper provides the first molecular study of the genus, employing molecular sequences from five mitochondrial (12S rDNA, 16S rDNA, COI, COIII, cytochrome oxidase b) and a single nuclear gene (rhodopsin) and includes representatives of each of the known Southern Ocean species. Thaumeledone rotunda, believed to be circumpolar in distribution and found in relatively deep water is the sister taxa to T gunteri, known only from South Georgia. A notable level of sequence variability was evident between a T peninsulae individual recently captured from the Powell Basin, and two T peninsulae individuals captured from the continental slope, north of the South Shetland Islands. This is likely to represent population level intraspecific variation within this species

The contribution of molecular data to our understanding of cephalopod evolution and systematics: a review

The first DNA sequence of a cephalopod was published in 1983 and the first molecular paper focusing on cephalopods was published in 1994. In this review we trace progress in the field. We examine the placement of Cephalopoda with respect to other molluscan classes and we examine relationships within Cephalopoda. We provide a summary tree of the relationships between cephalopod orders and we examine relationships of taxa within each of these orders. Although much knowledge has been gained over the past 20years, deeper-level relationships are still not well understood and there is still much scope for further research in this field. Genomic studies are likely to contribute significantly to our knowledge in the future

Redescription of the deep-sea octopod Benthoctopus normani (Massy 1907) and a description of a new species from the Northeast Atlantic

A long-synonymized species Benthoctopus normani (Massy 1907) (Cephalopoda: Octopodidae) is redescribed from material collected over 30 years by the National Oceanography Centre, Southampton and the National Museums of Scotland. It can be distinguished from other octopodid specimens found in deep waters of the Northeast Atlantic by its biserial suckers, lack of ink sac, and simple ligula, which lacks transverse ridges. Examination of the collections led to the identification of a new species of Benthoctopus from the Northeast Atlantic, which is described herein

Cranchiids of the South Atlantic Mid-Oceanic Ridge: results from the first southern MAR-ECO expedition

Cranchiids were the most diverse squid family collected during the first southern MAR-ECO expedition in late 2009, with nine taxa identified to species. A total of 45 young specimens were collected (mantle length 7.4-59.2mm), allowing a survey of early ontogenetic tentacular morphology in cranchiids using scanning electron micrographs. Paralarval tentacular sucker morphology appeared similar among species within the same subfamily: in the Cranchiinae, the paralarval suckers possess relatively large, narrowly polygonal or ovoid-faced pegs in the innermost ring around the aperture, and the infundibular ring lacks the dentition observed in most taoniin genera. Hook development in Galiteuthis armata appears to vary widely among small individuals. Tissue samples were also collected from five genera (Cranchia, Galiteuthis, Helicocranchia, Leachia and Teuthowenia); phylogenetic trees (maximum-likelihood and Bayesian methods) built using these cytochrome oxidase subunit I sequences and others available from GenBank show some support for the subfamilies Cranchiinae and Taoniinae, and that within the latter, the hooked taxa group together. It is hoped that reporting this opportunistic systematic and genetic information may be of eventual assistance in helping to resolve this most problematic of squid families

Persistent genetic signatures of historic climatic events in an Antarctic octopus

Repeated cycles of glaciation have had major impacts on the distribution of genetic diversity of the Antarctic marine fauna. During glacial periods, ice cover limited the amount of benthic habitat on the continental shelf. Conversely, more habitat and possibly altered seaways were available during interglacials when the ice receded and the sea level was higher. We used microsatellites and partial sequences of the mitochondrial cytochrome oxidase 1 gene to examine genetic structure in the direct-developing, endemic Southern Ocean octopod Pareledone turqueti sampled from a broad range of areas that circumvent Antarctica. We find that, unusually for a species with poor dispersal potential, P. turqueti has a circumpolar distribution and is also found off the islands of South Georgia and Shag Rocks. The overriding pattern of spatial genetic structure can be explained by hydrographic (with ocean currents both facilitating and hindering gene flow) and bathymetric features. The Antarctic Peninsula region displays a complex population structure, consistent with its varied topographic and oceanographic influences. Genetic similarities between the Ross and Weddell Seas, however, are interpreted as a persistent historic genetic signature of connectivity during the hypothesized Pleistocene West Antarctic Ice Sheet collapses. A calibrated molecular clock indicates two major lineages within P. turqueti, a continental lineage and a sub-Antarctic lineage, that diverged in the mid-Pliocene with no subsequent gene flow. Both lineages survived subsequent major glacial cycles. Our data are indicative of potential refugia at Shag Rocks and South Georgia and also around the Antarctic continent within the Ross Sea, Weddell Sea and off Adelie Land. The mean age of mtDNA diversity within these main continental lineages coincides with Pleistocene glacial cycles