Do plasticity in gene expression and physiological responses in Palaemonid prawns facilitate adaptive response to different osmotic challenges?

Integrating physiological and genomic approaches in a comparative framework offers excellent opportunity to investigate the underlying mechanisms for acclimation to specific challenges. The present study was conducted on three different prawn species (inhabitants of different salinity environments) of the genus Macrobrachium (M. australiense, M. tolmerum and M. novaehollandiae) to investigate the salinity induced changes in expression patterns of 10 candidate genes in the gill tissue (that previously had been inferred to play important functional roles in acclimation and adaptation to freshwater environments), and hemolymph osmolality. The prawn individuals were maintained in laboratory condition under three different salinity levels (0‰, 6‰ and 12‰) for 28 days using 6‰ as the control. All of the genes studied, showed salinity induced differential expression patterns. Genes with more important functional roles under low ionic conditions (i.e. Claudin, Na+/H+exchanger, V-type H+-ATPase and UNT2) showed 2.5 to 6 fold higher expression at 0‰ compared with at higher salinities (6‰ and 12‰) but no significant differences (p > 0.05) were observed between 6‰ and 12‰ for the same genes. In contrast, 1.5 to 4 fold higher expression levels were observed at 6‰ and 12‰ for genes that have important roles in mediating salinity tolerance (i.e., Na+/K+-ATPase, Na+/K+/2Cl-Co-transporter, Diuretic Hormone, Crustacean Hyperglycaemic Hormone and UNT1). The osmotic stress response gene, Calreticulin, showed significant differences (p < 0.05) in expression between different salinity comparisons. Hemolymph osmolality also was impacted in all three species with a strong correlation evident between hemolymph osmolality and expression of genes influencing this trait. Findings indicate an important role of plasticity that facilitates rapid acclimation to changing salinity levels.