Biomarkers of homeostasis, allostasis, and allostatic overload in decapod crustaceans of distinct habitats and osmoregulatory strategies: an empirical approach.

The term "allostasis", meaning the assumption that homeostasis may not be as static as the term implies, has been vastly employed for mammals, and other vertebrates, for which the degree of internal stability is maximal, according to their higher complexity. We have here investigated how these states of homeostasis, allostasis, and allostatic overload could be diagnosed in decapod crustaceans, upon acute salinity challenges. Decapods of distinct lineages and habitats have been submitted to 3 salinity levels for 6 and 12 h. The first salinity was the habitat salinity (control), considered as the one that allows the homeostatic condition. The next salinity represented a mild challenge, that would potentially lead to allostasis, and the third salinity was intended to represent an overload, albeit not lethal. Species used were: the marine crab Hepatus pudibundus (Hp, osmoconformer, salinities 33, 25, and 20‰), the marine/estuarine swimming crab Callinectes danae (Cd, weak regulator, salinities 30, 20, and 10‰), and the diadromous freshwater prawn Macrobrachium acanthurus (Ma, strong regulator, salinities <0.5, 15, and 30‰). These 3 species follow a sequence of growing regulatory capacity (Hp<Cd<Ma), and euryhalinity (Hp<Ma<Cd). The biomarker of allostatic overload in Hp was the dramatic build-up of hemolymph lactate in 10‰; Cd was so euryhaline that had its homeostasis barely disturbed by the treatments, and the overload biomarker for Ma was low reduced muscle hydration in 30‰. The concept of allostasis can be successfully applied to comparative osmoregulation of decapods, with potential implications in areas of applied physiology such as aquaculture.