Changes in Gene Expression of Ion Regulatory Proteins in Developing Atlantic Silverside (Menidia menidia) Subjected to Elevated Temperature and Acidity

Increases in temperature and acidity of the ocean affect survival, growth, and behavior of many marine organisms. With respect to ocean acidification, marine fishes have been shown to have variable responses to changing pH. One proposed mechanism for this variability is tied to their ability to regulate acid-base balance using ionocytes. Primarily studied in relation to osmoregulation of salt, ionocytes also regulate acid balance with ion exchangers and ion pump ATPases. These proteins may play a key role in acclimation to acidification of marine coastal habitats. The present study aims to determine the combined effects of temperature and acidity on the expression of genes associated with ion regulation in developing Atlantic silversides (Menidia menidia) in a controlled laboratory setting. Real-time quantitative PCR was used to compare the expression of osmoregulatory proteins in one- and ten-days post hatch larvae raised under three pH levels, and three temperatures. Temperature and pH interacted such that the expression of four genes (NKA, NHE3, NKCC1, and NKCC2) to varying levels of pH was dependent on temperature. As expected, the response varied with age reflecting the development of ionocytes and ability to express osmoregulatory proteins, potentially explaining the vulnerability of some marine fish at very young stages. The observed changes in gene expression may reflect transitions between different homeostatic states. Analyses such as this, of the combined effects of different factors involved in acidification of coastal environment, will refine our understanding of the extent to which fish can acclimate to environmental stressors.