Description: Population substructure of the cuttlefish Sepia officinalis (Mollusca: Cephalopoda), as investigated by genetic variation of microsatellite loci, has been reported to be significantly extensive around the Iberian Peninsula with FST = 0.061 [Pérez-Losada, M., Guerra, A., Carvalho, G.R., Sanjuan, A., Shaw, P.W., 2002. Extensive population subdivision of the cuttlefish Sepia officinalis (Mollusca: Cephalopoda) around the Iberian Peninsula indicated by microsatellite DNA variation. Heredity 89, 417–424] and panmictic in the semi-enclosed Adriatic Sea with FST = 0.011 [Garoia, F., Guarniero, I., Ramsak, A., Ungaro, N., Landi, M., Piccinetti, C., Mannini, P., Tinti, F., 2004. Microsatellite DNA variation reveals high gene flow and panmictic populations in the Adriatic shared stocks of the European squid and cuttlefish (Cephalopoda). Heredity 93, 166–174]. Yet, no verified genetic information on population substructure existed for the northern distribution range of this species in the English Channel and the Bay of Biscay. So far, reproductive and migration behaviour and in vitro oxygen binding properties of haemocyanin have suggested the existence of separate populations in the English Channel and the Bay of Biscay. Examination of genetic variation at seven microsatellite loci within samples from the Bay of Biscay, the English Channel and the southern North Sea indicated low levels of genetic differentiation in this area but also a breakdown of free gene flow at highly significant average FST = 0.018. Although there is a considerable genetic exchange between populations of S. officinalis in the English Channel and the Bay of Biscay, they cannot be regarded as a single, freely interbreeding population. Earlier reported biological differences might thus be due to genetic variability between the populations.

Description: Abstract Research investigating the genetic basis of physiological responses has significantly broadened our understanding of the mechanisms underlying organismic response to environmental change. However, genomic data are currently available for few taxa only, thus excluding physiological model species from this approach. In this study we report the transcriptome of the model organism Hyas araneus from Spitsbergen (Arctic). We generated 20,479 transcripts, using the 454 {GS} {FLX} sequencing technology in combination with an Illumina HiSeq sequencing approach. Annotation by Blastx revealed 7159 blast hits in the {NCBI} non-redundant protein database. The comparison between the spider crab H. araneus transcriptome and {EST} libraries of the European lobster Homarus americanus and the porcelain crab Petrolisthes cinctipes yielded 3229/2581 sequences with a significant hit, respectively. The clustering by the Markov Clustering Algorithm (MCL) revealed a common core of 1710 clusters present in all three species and 5903 unique clusters for H. araneus. The combined sequencing approaches generated transcripts that will greatly expand the limited genomic data available for crustaceans. We introduce the {MCL} clustering for transcriptome comparisons as a simple approach to estimate similarities between transcriptomic libraries of different size and quality and to analyze homologies within the selected group of species. In particular, we identified a large variety of reverse transcriptase (RT) sequences not only in the H. araneus transcriptome and other decapod crustaceans, but also sea urchin, supporting the hypothesis of a heritable, anti-viral immunity and the proposed viral fragment integration by host-derived {RTs} in marine invertebrates.