Gene expression in the intertidal mussel Mytilus californianus: physiological response to environmental factors on a biogeographic scale

We used a cDNA microarray to profile gene expression in the intertidal mussel Mytilus californianus across major portions of its biogeographic range. Overall, the expression pattern for the majority of genes assessed in this study varied significantly as a function of collection site and provides support for the hypothesis that the physiological response to emersion is distinct across populations of M. californianus. Gill tissue was dissected from adult, field-acclimatized M californianus collected from 4 sites across 17 degrees of latitude along the west coast of North America. First-strand cDNA prepared from 5 biological replicates from each site were competitively hybridized to a 2496 feature cDNA microarray. Gene expression patterns in mussels from Strawberry Hill, Oregon, displayed a unique expression phenotype that was distinct from them other 3 mussel populations sampled. In contrast, mussels sampled from Bamfield, British Columbia, and Jalama Beach, California, showed similar expression patterns. These data suggest that the physiological response of M californianus to abiotic factors, such as temperature, cannot be predicted by a simple latitudinal gradient. This study highlights the usefulness of genomics-based approaches in assessing physiological responses to environmental variation across large spatial scales.