Owing to its evolutionary history, the family Palaemonidae unites extant species from widely distinct osmotic environments like marine, estuarine and fresh waters, including osmotically stable or variable habitats. These shrimps compensate physiologically for osmotic challenge at both the systemic and cellular levels, employing homeostatic mechanisms that regulate the water and electrolyte concentrations of their body fluids. The gill epithelium constitutes an important interface of compensatory ion transport, and its ionocyte membranes express ion transporters that provide transepithelial ion movements. The Na+, K+, 2Cl- cotransporter (NKCC) plays a significant role in compensatory salt uptake and secretion, also participating in cell volume regulation by non-epithelial cells. In this study, we will establish a role for the NKCC in palaemonids from the genera Macrobrachium, Palaemonetes and Palaemon that occupy different osmotic niches and exhibit distinct osmoregulatory patterns. We will examine the effect of salinity exposure on hemolymph osmolality and Cl- concentration, and on quantitative gill NKCC gene and protein expression, employing molecular and biochemical analyses, including the location of the NKCC in the ionocytes membranes by immunofluorescence microscopy. Consequent to our molecular, morphological and physiological characterization, we will examine the hypotheses of: (i) a salinity effect on the evolution of hemolymph Cl- regulatory capacity and NKCC gene and protein expression; and (ii) the existence of a phylogenetic pattern in these parameters. Employing such phylogenetic comparative methods will allow reconstruction of the evolutionary history of osmoregulation at the molecular, cellular and systemic levels in the palaemonids investigated.
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