25. Elevated CO2 induces different molecular responses from selectively bred and wild Sydney rock oysters (Saccostrea glomerata)

Thompson, Emma L. (1)*, O’Connor, Wayne (2), Parker, Laura (3), Ross, Pauline (4), Raftos, David (5)

1 Department of Biological Sciences, Macquarie University, Sydney, NSW, 2199
2 NSW Department of Primary Industries Port Stephens Fisheries Research Institute, Taylors Beach, NSW, 2316
3 Department of Biological Sciences, University of Sydney, Sydney, NSW
4 Department of Biological Sciences, University of Sydney, Sydney, NSW
5 Department of Biological Sciences, Macquarie University, Sydney, NSW, 2199

Background
Previous work suggests that larvae from Sydney rock oysters that have been selectively bred for fast growth and disease resistance are more resilient to the impacts of ocean acidification than non-selected, wild type oysters. In the current study, we used proteomics to investigate the molecular differences between adults in these two oyster populations, and to identify if these form the basis for observations seen in larvae.

Methods
Adult oysters from a selective breeding line (B2) and non-selected wild types (WT) were exposed for four weeks to ambient (375 µatm) or elevated pCO2 (856 µatm). Proteomic analysis and mass spectrometry was undertaken and the proteomes of each population at both treatments compared.

Findings
Exposure to elevated pCO2 resulted in substantial changes in the proteomes of oysters from both the selectively bred and wild type populations. In the wild type population, 95% of differentially expressed proteins were upregulated (2 to 54 fold increases in intensity). However, unexpectedly in the selectively bred population proteins were all downregulated (-2 to -59 fold decreases). When biological functions were assigned, these differential proteins fell into five broad, potentially interrelated categories of subcellular functions, in both oyster populations. These functional categories were energy production, cellular stress responses, the cytoskeleton, protein synthesis and cell signaling.

Conclusions
This study suggests that CO2 exposure on non-selected wild type Sydney rock oysters activates an inducible stress response similar to responses we have seen from other environmental impacts.

The unexpected results in the selectively bred oysters may reflect cellular dysfunction and a tradeoff between adult oysters and developmental success of larvae. An adaptive capacity for enhanced mitochondrial energy production in the selectively bred population may help to protect larvae from the effects of elevated CO2, but be detrimental to adult oysters.