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Phenotypic Adaptation of an Arctic Copepod to Ocean Acidification

Paper Reviewed
Bailey, A., De Wit, P., Thor, P., Browman, H.I., Bjelland, R., Shema, S., Fields, D.M., Runge, J.A., Thompson, C. and Hop, H. 2017b. Regulation of gene expression is associated with tolerance of the Arctic copepod Calanus glacialis to CO2-acidified sea water. Ecology and Evolution 7: 7145-7160.

In a previous study, Bailey et al. (2017a) investigated the impacts of increased pCO2 on a key Arctic copepod, Calanus glacialis, exposing wild-caught C. glacialis eggs to four pH/pCO2 levels (pH 8.05/320 µatm, pH 7.90/530 µatm, pH 7.70/800 µatm and pH 7.50/1700 µatm) for a period of two months. Results of that analysis revealed that C. glacialis was not affected by low pH, as determined by multiple measurements of respiration, ingestion, survival, gonad maturation, egg production, growth and development through the sixth naupliar stage.

In conjunction with that study, a second team of authors (Bailey et al., 2017b) collected nauplii samples from each pH treatment when their development reached stage N6 (35-38 days post-egg laying) from which they extracted and sequenced mRNA in an effort to investigate the gene expression patters of the naupli cultured in the four different pH treatments. Results of this second experiment revealed that of the 59,353 contigs identified in the de novo transcriptome, 151 (~ 0.25%) were identified as significantly differentially expressed (DE) between pH 7.5 and 8.05. Of these 151 DE contigs, 140 (93%) were downregulated, many of which were related to cellular stress responses, including DNA repair, redox regulation, protein folding and proteolysis. Among the 11 upregulated contigs, they tended to include processes and functions that pertained to maintaining cellular pH homeostatis and locomotion.

Commenting on their findings, Bailey et al. (2017b) write that "the downregulation of the majority of differentially expressed contigs in this study can reasonably be interpreted as an indication that C. glacialis is naturally tolerant of lowered pH, which is consistent with the organismal-level tolerance measured on the same nauplii [as reported in Bailey et al., 2017a]." Additionally, they write that "the upregulation of [differentially expressed contigs] may contribute to C. glacialis' response to low pH without adding additional [metabolic] cost." And in light of these combined findings, the authors conclude that "altered gene expression allowed C. glacialis to phenotypically buffer the change in pH, thereby maintaining normal nauplii development."

Bailey, A., Thor, P., Browman, H.I., Fields, D.M., Runge, J., Vermont, A., Bjelland, R., Thompson, C., Shema, S., Durif, C.M.F. and Hop, H. 2017a. Early life stages of the Arctic copepod Calanus glacialis are unaffected by increased seawater pCO2. ICES Journal of Marine Science 74: 996-1004.

Posted 2 February 2018