Temperature and salinity stress in Eurytemora affinis: Defining ecological limits using protein expression

The geographical and seasonal distribution of the copepod Eurytemora affinis in the Chesapeake Bay seems to be limited by salinity and temperature. Results in the laboratory suggest E. affinis should be able to accommodate to the entire range of salinity temperature combinations encountered. Yet at high temperatures (>20°C) and salinities (>20 ppt) in particular E. affinis is not found. In this study I examined changes in overall protein expression in E. affinis exposed to extreme temperature-salinity combinations as well as to the salinity-temperature combinations in which they are commonly found in the Chesapeake Bay. Protein expression can be directly related to stress in that proteins are used by copepods to adapt to changing salinities and temperatures. The number of proteins present or absent compared to intermediate conditions tended to increase with the degree of stress. The high temperature and high salinity treatment had the highest number of protein changes.; Copepods were also exposed to extreme salinities and temperatures over 4, 8 and 12 h in a factorial design. The highest number of protein changes was seen in the 4 h exposed copepods. Both the 8 and 12 h exposed copepods had fewer present proteins and had a high number of absent proteins versus the control. In addition to examining protein expression over time, I examined protein expression of field-collected E. affinis, sampled from Baltimore Harbor. The protein expression seen in these copepods had a high number of protein changes (both present and absent proteins) versus the control.; The identification of two proteins thought to aid in adaptation to salinity was attempted. A protein thought to be Na-K ATPase, a protein likely to be part of the mechanism of salinity adaptation, was not confirmed using peptide mass fingerprinting. The protein presumed to be glutamate dehydrogenase (GDH), a protein involved in the regulation of free non-essential amino acids, was identified using a peptide antibody. GDH appeared to be expressed in the higher salinity, higher temperature treatments. Isolation and identification of sets of such proteins will lead to a clearer understanding of the physico-chemical limits to natural populations of E. affinis.