Contrasting strategies of osmotic and ionic regulation in freshwater crabs and shrimps: gene expression of gill ion transporters.

Owing to their extraordinary niche diversity, the Crustacea are ideal for comprehending the evolution of osmoregulation. The processes that effect systemic hydro-electrolytic homeostasis maintain hemolymph ionic composition via membrane transporters located in highly specialized gill ionocytes. We evaluated physiological and molecular hyper- and hypo-osmoregulatory mechanisms in two phylogenetically distant, freshwater crustaceans, the crab and the shrimp , when osmotically challenged for up to 10 days. When in distilled water, survived without mortality, hemolymph osmolality and [Cl] increased briefly, stabilizing at initial values, while [Na] decreased continually. Expression of gill V-type H-ATPase (V-ATPase), Na/K-ATPase and Na/K/2Cl symporter genes was unchanged. In , hemolymph osmolality, [Cl] and [Na] decreased continually for 12 h, the shrimps surviving only around 15-24 h exposure. Gill transporter gene expression increased 2- to 5-fold. After 10 days exposure to brackish water (25‰S), was isosmotic, iso-chloremic and iso-natriuremic. Gill V-ATPase expression decreased while Na/K-ATPase and Na/K/2Cl symporter expression was unchanged. In (20‰S), hemolymph was hypo-regulated, particularly [Cl]. Transporter expression initially increased 3- to 12-fold, declining to control values. Gill V-ATPase expression underlies the ability of to survive in fresh water while V-ATPase, Na/K-ATPase and Na/K/2Cl symporter expression enables to confront hyper/hypo-osmotic challenges. These findings reveal divergent responses in two unrelated crustaceans inhabiting a similar osmotic niche. While does not secrete salt, tolerating elevated cellular isosmoticity, exhibits clear hypo-osmoregulatory ability. Each species has evolved distinct strategies at the transcriptional and systemic levels during its adaptation to fresh water.