Henry 9727835 The physical factors in an organism's environment often exert pressure on the organism to evolve specific physiological responses (adaptations) in order to survive in and exploit that environment. One of the richest aquatic environments is the estuary, with high concentrations of nutrients and low numbers of competing species. However, estuaries are harsh and hostile with respect to their primary physical characteristic, low and fluctuating salinity. Estuarine species have evolved specific mechanisms for survival in low salinity. Specifically, they have the ability to take up salt (Na and C1 ions) from the ambient water into their blood, thus allowing them to maintain fairly constant blood and tissue concentrations even in the face of highly variable environmental salt concentrations. This is accomplished through the action of specific salt-transport enzymes, the Na/K ATPase and carbonic anhydrase. The levels of these enzymes are induced in low salinity, but the process of induction is unknown. The focus of this research is the mechanism by which an organism perceives a salinity change and transduces that into the selective induction of transport enzymes.
