Transcriptional Profiling of Populations in the Clam Ruditapes decussatus Suggests Genetically Determined Differentiation in Gene Expression along Parallel Temperature Gradients and between Races of the Atlantic Ocean and West Mediterranean Sea

Ongoing ocean warming due to climate change poses new challenges for marine life and its exploitation. We have used transcriptomics to find genetically based responses to increased temperature in natural populations of the marine clam Ruditapes decussatus, which lives along parallel thermal gradients in southern Europe. Clams of the Atlantic and West Mediterranean races were collected in northern (cool) and a southern (warm) localities. The animals were kept in running seawater in the warm, southern Atlantic locality for a 15-week period. During this period, water temperature was raised to typical southern European summer values. After this period, an expression profile was obtained for a total of 34 clams and 11,025 probes by means of an oligonucleotide microarray. We found distinct transcriptional patterns for each population based on a total of 552 differentially expressed genes (DEGs), indicating innate differences which probably have a genetic basis. Race and latitude contributed significantly to gene expression differences, with very different sets of DEGs. A gene ontology analysis showed that races differed mainly in the genes involved in ribosomal function and protein biosynthesis, while genes related to glutathione metabolism and ATP synthesis in the mitochondria were the most outstanding with respect to north/south transcriptional differences.