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SYMPOSIUM on Marine Accidental Oil Spills Wild mussels from Northern Iberian Peninsula are genetically identified as Mytilus galloprovincialis according to the Glu-5’ DNA marker Ionan MARIGÓMEZ, Larraitz GARMENDIA, Eider BILBAO, Ibon CANCIO, Miren P. CAJARAVILLE Laboratory of Cell Biology & Histology, Department of Zoology & Animal Cell Biology, School of Science & Technology, University of the Basque Country, PO BOX 644, E-48080 Bilbo, Basque Country, Spain ABSTRACT Although the overall consensus sets up that mussels in the Northern Iberian Peninsula belong to the species Mytilus galloprovincialis, mussels from this geographical area have been repeatedly reported to as M. edulis, even in various contributions assessing the effects of the Prestige oil spill. Several morphologically similar taxa (M. edulis, M. galloprovincialis, M. californianus and M. trossulus) have been reported within the genus Mytilus and, in addition, where two of these species are in geographical contact, hybridisation may occur (Inoue et al., 1995). According to previous reports, M. edulis and M. galloprovincialis exhibit either sympatry or allopatry, with various degrees of hybridisation, over more than 1000 km of Atlantic coastline in Western Europe (Hilbish et al., 2002; Gilg and Hilbish 2003). The distribution of these species and their hybrids has been proposed to be governed by abiotic environmental factors (temperature, tide level and salinity), which evidences that they posses distinct adaptive capacities (Braby & Somero 2006; Hilbish et al., 1994). Taxonomical identification is therefore crucial in biomonitoring programmes in order to achieve a correct interpretation of biomarkers and disease records, as well as to implement integrative genomic and proteomic approaches. The objective of the present study was the taxonomical identification of mussels used as sentinels in the monitoring programme carried out to assess the biological effects of the Prestige oil spill. For this purpose, the region of the non-repetitive domains of the adhesive protein gene Glu’5 was examined by the polymerase chain reaction, as a species specific genetic marker, in mussels collected in 22 localities from Portugal to the Basque coast in October 2004. DNA was extracted from 10 individuals per sampling locality and Me15 and Me16 primers were used to amplify the above described portion of the Glu’5 gene (Inoue et al., 1995). M. edulis from Førlandsfjord (Norway) and M. galloprovincialis from Saronikos Gulf (Greece) were employed as reference controls. With this primer couple an amplicon 180 bp long would identify an individual as M. edulis, while a fragment 126 bp long would appear in the case of M. galloprovincialis due to a deletion of 18 amino acids in the corresponding protein (Inoue and Odo, 1994). Hybrids can be also identified since two bands of 180 bp and 126 bp would result amplified in hybrid individuals. Presently, one specific single band of 126 bp was clearly identified in all the samples analysed from Portugal to the Basque coast as well as in Mediterranean mussels. Mussels from North Sea, on the other hand, presented one 180 bp band. These results confirm that all the wild mussels from Northern Iberian Peninsula used as sentinels to assess the biological effects of the Prestige oil spill belong to the species M. galloprovincialis and therefore differences found during the biomonitoring programme (Orbea et al., 2006; Marigómez et al., 2006) can not be attributed to the presence of different taxa in different localities along the study area. Funded by the Spanish MEC (VEM2003-20082-CO6-01), Basque Government (ETORTEK actions-IMPRES) and the University of the Basque Country (Grant to Consolidated Research Groups). REFERENCES Braby CE & Somero GN. 2006. Ecological gradients and relative abundance of native (Mytilus trossulus) and invasive (Mytilus galloprovincialis) blue mussels in the California hybrid zone. Mar. Biol. 148: 1249-1262 Gilg MR & Hilbish TJ. 2003. Spatio-temporal patterns in the genetic structure of recently settled blue mussels (Mytilus spp) across a hybrid zone. Mar. Biol. 143: 679-690 Hilbish T, Brian L, Day A. 1994. Genetics of physiological differentiation within the marine mussel genus Mytilus. Evolution 48: 267-286 Inoue K & Odo S. 1994. The adhesive protein cDNA of Mytilus galloprovincialis encodes decapeptide repeats but no hexapeptide motif. Biol. Bull. 186: 349-355 Inoue K, Waite H, Matsuoka M, Odo S, Harayama S. 1995. Interspecific variations in adhesive protein sequences of Mytilus edulis, M. galloprovincialis and M. trossulus. Biol. Bull. 189: 370-375 Marigómez I, Soto M, Cancio I, Orbea A, Garmendia L, Cajaraville MP. 2006. Cell and tissue biomarkers in mussel, and histopathology in hake and anchovy from Bay of Biscay after the Prestige oil spill (Monitoring Campaign 2003). Mar. Poll. Bull. 53: 287-304 Orbea A, Garmendia L, Marigómez I, Cajaraville MP. 2006.Effects of the ‘Prestige’ oil spill on cellular biomarkers in intertidal mussels: results of the first year of studies. Mar. Ecol. Prog. Ser. 306: 177-189 1