Abstract
Ocean acidification is the increase in seawater pCO 2 due to the uptake of atmospheric anthropogenic CO 2, with the largest changes predicted to occur in the Arctic seas. For some marine organisms, this change in pCO 2, and associated decrease in pH, represents a climate change‐related stressor. In this study, we investigated the gene expression patterns of nauplii of the Arctic copepod Calanus glacialis cultured at low pH levels. We have previously shown that organismal‐level performance (development, growth, respiration) of C. glacialis nauplii is unaffected by low pH. Here, we investigated the molecular‐level response to lowered pH in order to elucidate the physiological processes involved in this tolerance. Nauplii from wild‐caught C. glacialis were cultured at four pH levels (8.05, 7.9, 7.7, 7.5). At stage N6, mRNA was extracted and sequenced using RNA‐seq. The physiological functionality of the proteins identified was categorized using Gene Ontology and KEGG pathways. We found that the expression of 151 contigs varied significantly with pH on a continuous scale (93% downregulated with decreasing pH). Gene set enrichment analysis revealed that, of the processes downregulated, many were components of the universal cellular stress response, including DNA repair, redox regulation, protein folding, and proteolysis. Sodium:proton antiporters were among the processes significantly upregulated, indicating that these ion pumps were involved in maintaining cellular pH homeostasis. C. glacialis significantly alters its gene expression at low pH, although they maintain normal larval development. Understanding what confers tolerance to some species will support our ability to predict the effects of future ocean acidification on marine organisms.
Highlights
Anthropogenic CO2 emissions are increasing the pCO2 of the atmosphere and the oceans (Le Quéré, Raupach, & Canadell, 2009).Increased pCO2 in surface waters alters the carbonate chemistry of sea water, increasing hydrogen ion (H+), bicarbonate ion (HCO3−), and dissolved inorganic carbon (DIC) concentrations and decreasing pH and carbonate ion (CO32−) concentrations
We expected that the physiological functions affected by pH, as indicated by altered expression of genes coding for functional groups of proteins, would be similar to those affected in other marine organisms at low pH and would, contribute to an understanding of a generalized molecular response to low pH
C. glacialis nauplii were tolerant of pH levels relevant for future ocean acidification scenarios
Summary
Anthropogenic CO2 emissions are increasing the pCO2 of the atmosphere and the oceans (Le Quéré, Raupach, & Canadell, 2009). The ability of an organism to maintain fitness-related traits, like growth, reproduction, and development, while exposed to a stressful environment by adjusting underlying physiological processes has been referred to as phenotypic buffering (Reusch, 2014). Understanding the mechanisms of phenotypic buffering that allow some species to tolerate a wide range of pH is important for the field of ocean acidification research. Can it help detect low-level stress potentially unnoticed in organismal-level measurements, but it contributes to understanding how some species, but not others, can tolerate low pH. We expected that the physiological functions affected by pH, as indicated by altered expression of genes coding for functional groups of proteins, would be similar to those affected in other marine organisms at low pH and would, contribute to an understanding of a generalized molecular response to low pH
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