Listmann, Luisa (2014) Gene expression analysis in Atlantic herring (Clupea harengus) in response to temperature and CO2. (Master thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 52 pp.

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Abstract

Major perturbations associated with climate change are decreases in ocean pH levels (ocean acidification, OA) and the increase of mean and variance in temperature. Early life stages such as larval fish may be particularly vulnerable to such stressors either alone or in combination. Earlier studies have established strong phenotypic effects on larval herring such as a decrease in RNA/DNA ratio as a response to hypercapnia or behavioural changes. As an ecologically and economically important fish species studies on the tolerance of Atlantic herring to cope with an altered environment are of prime interest. I quantified gene expression of 32 target genes in larval Atlantic herring and correlated the patterns with identified phenotypic responses to hypercapnia and temperature increase. In a first experiment larvae were kept under three different levels of C02 (380, 1800 and 4200µatm). A second major objective was to address the interaction of OA with temperature which was fully crossed (3°C higher than ambient) with C02 environment (ambient and lOOOppm) in a second experiment. Samples were taken at several time points so as to detect windows of sensitivity to OA and warming stressors. I selected 32 candidate genes putatively involved in acid base regulation, heat stress regulation, immune system response and metabolism. Gene expression levels were quantified using the Dynamic ArrayTM IFC Chip gene expression method (Fluidigm®). When disentangling the different responses and levels of response of Atlantic herring to environmental stress, two different stress responses were detected: hormesis and phenotypic buffering. On the one hand, in response to the three different levels of C02 a dose dependent response - hormesis - could be seen. On the other hand, C02 and temperature together showed a compensatory effect on gene expression level and apparently no effect on the phenotype indicating the larvae's ability to maintain a functioning phenotype in a changed environment which is described by phenotypic buffering. However, the effect of ocean acidification and warming in an environmentally varying coastal habitat in which herring larvae develop with daily fluctuations in temperature and C02 may be underestimated by the levels of C02 of this study.

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