Identification of molecular and physiological responses to chronic environmental challenge in an invasive species: the Pacific oyster, Crassostrea gigas

Abstract

Understanding the environmental responses of an invasive species is critical in predicting how ecosystem composition may be transformed in the future, especially under climate change. In this study, Crassostrea gigas, a species well adapted to the highly variable intertidal environment, was exposed to the chronic environmental challenges of temperature (19 and 24°C) and pH (ambient seawater and a reduction of 0.4 pH units) in an extended 3-month laboratory-based study. Physiological parameters were measured (condition index, shell growth, respiration, excretion rates, O:N ratios, and ability to repair shell damage) alongside molecular analyses. Temperature was by far the most important stressor, as demonstrated by reduced condition indexes and shell growth at 24°C, with relatively little effect detected for pH. Transcriptional profiling using candidate genes and SOLiD sequencing of mantle tissue revealed that classical “stress” genes, previously reported to be upregulated under acute temperature challenges, were not significantly expressed in any of the treatments, emphasizing the different response between acute and longer term chronic stress. The transcriptional profiling also elaborated on the cellular responses underpinning the physiological results, including the identification of the PI3K/AKT/mTOR pathway as a potentially novel marker for chronic environmental challenge. This study represents a first attempt to understand the energetic consequences of cumulative thermal stress on the intertidal C. gigas which could significantly impact on coastal ecosystem biodiversity and function in the future.

Interactive effects of seawater acidification and elevated temperature on biomineralization and amino acid metabolism in the musselMytilus edulis

“…The echinoderms and shelled molluscs are vulnerable to seawater acidification and warming because their calcified tissues are formed from highly soluble crystals (Dupont et al, 2010). Consistent with the result for Pacific oyster C. gigas (Clark et al, 2013), elevated temperature enhanced the effect of seawater acidification on NCR in M. edulis. In addition to NCR, elevated temperature also enhanced the reduction in Ca/Mg ratio caused by seawater acidification.…”

Key metabolic pathways involved in xenobiotic biotransformation and stress responses revealed by transcriptomics of the mangrove oyster Crassostrea brasiliana

“…HSP70 genes have previously shown strong correlation with chemical exposure, including hydrocarbons as used in this study, and have been suggested as candidate biomarkers for environmental toxicology (Boutet et al, 2004;Cruz-Rodríguez and Chu, 2002;Snyder et al, 2001). In these studies the inducible form of HSP70 was targeted in a candidate gene approach, as these were the only gene data available at the time, but more recent analyses have shown HSP70-12B to be induced in response to thermal challenge in C. gigas (Clark et al, 2013). Table 4 should be placed here…”

“…The latter method may prove particularly useful where there is an expansion in gene family members and it is not necessarily the "classical", best known family members that are responsive to the chemical or environmental challenge (c.f. Clark and Peck, 2009a;Clark et al, 2013). Also these represent laboratory-induced experiments and there is an additional requirement to link these through to responses in the natural environment, as the two types of exposure and the associated stress response may not be equivalent (c.f.…”

Rapid transcriptional acclimation following transgenerational exposure of oysters to ocean acidification

“…() and Clark et al . () have also performed comprehensive transcriptomic analyses assessing the response of C. virginica and C. gigas , respectively, to a combination of OA and ocean warming. Decreasing pH was shown to increase the immune functions and production of antioxidants in C. gigas , while the combination of both pH and thermal stress induced the expression of protease inhibitors and cytoskeleton‐related genes (Clark et al .…”