Gene expression responses to increased pCO2 in the Arctic copepod Calanus glacialis

Chair: Vonda Cummings

Allison Bailey (1)*, Pierre de Wit (2), Peter Thor (1), Howard I. Browman (3), David Fields (4), Jeffrey Runge (5), Alex Vermont (4), Reidun Bjelland (3), Cameron Thompson (5), Steven Shema (3), Caroline Durif (3), Haakon Hop (1)

1 Norwegian Polar Institute, Tromsø, 9296, Norway
2 University of Gothenburg, Sven Lovén Centre for Marine Sciences, Tjärnö, 45296 Sweden
3 Institute of Marine Research, Austevoll Research Station, Storebø 5392, Norway
4 Bigelow Laboratory for Ocean Sciences, East Boothbay, Maine, 04544, USA
5 Gulf of Maine Research Institute, University of Maine, Orono, Maine, USA

Background
Marine organisms experience variability in their environment on daily, seasonal, and, increasingly, decadal time scales. Their ability to maintain physiological functioning and fitness despite short-term changes in environmental drivers is referred to as phenotypic buffering. An organism’s capacity for phenotypic buffering may indicate how they will tolerate changes on longer time scales. Up- or down-regulation of gene expression likely underpins phenotypic buffering. In this study we investigated the gene expression patterns of nauplii of the Arctic copepod Calanus glacialis subjected to pCO2 levels relevant for future projections of ocean acidification. As their development and growth appears to be unaffected by these pCO2 levels, this study sought to understand whether altered gene expression was the mechanism by which they phenotypically buffered this environmental gradient.

Methods
Nauplii from wild-caught Calanus glacialis were cultured at four pCO2 regimes (320, 530, 800, 1700) for two months. Two pooled samples of nauplii were collected from each of three replicate culture tanks per pCO2 treatment (24 total), the RNA extracted and the transcriptome sequenced using RNAseq.

Findings
A de novo transcriptome was compiled, contigs identified, and the associated proteins annotated using BLASTx and KEGG pathways. Then, RNA sequences from each sample were mapped to the de novo transcriptome to produce a proxy of gene expression of individual genes. Further, differential gene expression between the pCO2 treatments will be tested both for individual genes and functional groups of genes.

Conclusions
Relative up- or down-regulation of gene expression by nauplii subjected to the four pCO2 levels will elucidate the mechanism by which copepod larvae may maintain fitness at pCO2‘s projected for ocean acidification. Identification of specific genes or metabolic pathways involved will further help us understand if C. glacialis will be able to maintain this phenotypic buffering over the long-term in response to future ocean acidification.