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Previous research on the Antarctic notothenioid fish Trematomus bernacchii demonstrated the loss of the heat shock response (HSR), a classical cellular defense mechanism against thermal stress, characterized by the rapid synthesis of heat shock proteins (Hsps). In the current study, we examined potential mechanisms for the apparent loss of the HSR in Antarctic notothenioids and, in addition, compared expression patterns of two genes from the 70-kDa Hsp family (hsc71 and hsp70) in tissues from T. bernacchii to expression patterns in tissues of two closely related temperate notothenioid fishes from New Zealand, Bovichtus variegatus and Notothenia angustata. The results showed that transcript for both the constitutive and inducible genes in the Hsp70 gene family were expressed in detectable levels in all three species. However, only the cold-temperate New Zealand fishes displayed the ability to upregulate the inducible transcript, hsp70. Although hsp70 was present in detectable levels in several tissues of the Antarctic notothen T. bernacchii, in vitro thermal stresses failed to produce a significant increase in mRNA levels. In all species, the expression of the constitutive transcript hsc71 was variable and nonresponsive to temperature increases, even at temperatures as high as 10 degrees C above the ecologically relevant range for the species under study. Field-collected tissues from T. bernacchii (sampled immediately after capture) indicated that hsp70 mRNA was expressed at high levels in field-acclimatized fishes. Thus upregulation of molecular chaperones suggested that low-temperature stress may be significantly denaturing to cellular proteins in Antarctic fish, an observation that was supported by elevated levels of ubiquitin-conjugated protein.

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, fieldacclimatized M. californianus collected from 4 sites across 17°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 the 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 genomicsbased approaches in assessing physiological responses to environmental variation across large spatial scales.

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patterns, in hepatocytes from T. bernacchii. Hsp70 mRNA was detected, as was heat shock factor 1 (HSF1) with DNA-binding activity. However, exposure to elevated temperature and to chemical inducers of the heat shock response failed to increase Hsp70 mRNA levels, HSF1 activity or the concentration of any size class of Hsps. These results suggest that Hsps, inducible in nearly every other species, are expressed constitutively in the coldadapted T. bernacchii.

Antarctic fish of the suborder Notothenioidei have evolved several unique adaptations to deal with subzero temperatures. However, these adaptations may come with physiological trade-offs, such as an increased susceptibility to oxidative damage. As such, the expected environmental perturbations brought on by global climate change have the potential to significantly increase the level of oxidative stress and cellular damage in these endemic fish. Previous single stressor studies of the notothenioids have shown they possess the capacity to acclimate to increased temperatures, but the cellularlevel effects remain largely unknown. Additionally, there is little information on the ability of Antarctic fish to respond to ecologically relevant environmental changes where multiple variables change concomitantly. We have examined the potential synergistic effects that increased temperature and Ṗ CO2 have on the level of protein damage in Trematomus bernacchii, Pagothenia borchgrevinki and Trematomus newnesi, and combined these measurements with changes in total enzymatic activity of catalase (CAT) and superoxide dismutase (SOD) in order to gauge tissue-specific changes in antioxidant capacity. Our findings indicate that total SOD and CAT activity levels displayed only small changes across treatments and tissues. Short-term acclimation to decreased seawater pH and increased temperature resulted in significant increases in oxidative damage. Surprisingly, despite no significant change in antioxidant capacity, cellular damage returned to near-basal levels, and significantly decreased in T. bernacchii, after long-term acclimation. Overall, these data suggest that notothenioid fish currently maintain the antioxidant capacity necessary to offset predicted future ocean conditions, but it remains unclear whether this capacity comes with physiological trade-offs.

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Summary The marine intertidal zone is characterized by large variation in temperature, pH, dissolved oxygen and the supply of nutrients and food on seasonal and daily time scales. These oceanic fluctuations drive of ecological processes such as recruitment, competition and consumer-prey interactions largely via physiological mehcanisms. Thus, to understand coastal ecosystem dynamics and responses to climate change, it is crucial to understand these mechanisms. Here we utilize transcriptome analysis of the physiological response of the mussel Mytilus californianus at different spatial scales to gain insight into these mechanisms. We used mussels inhabiting different vertical locations within Strawberry Hill on Cape Perpetua, OR and Boiler Bay on Cape Foulweather, OR to study inter- and intra-site variation of gene expression. The results highlight two distinct gene expression signatures related to the cycling of metabolic activity and perturbations to cellular homeostasis. Intermediate spatial scales show a strong influence of oceanographic differences in food and stress environments between sites separated by ~65 km. Together, these new insights into environmental control of gene expression may allow understanding of important physiological drivers within and across populations.