RESUMO
Osmoregulatory findings on crabs from high Neotropical latitudes are entirely lacking. Seeking to identify the consequences of evolution at low temperature, we examined hyperosmotic/hypo-osmotic and ionic regulation and gill ion transporter gene expression in two sub-Antarctic Eubrachyura from the Beagle Channel, Tierra del Fuego. Despite sharing the same osmotic niche, Acanthocyclus albatrossis tolerates a wider salinity range (2-65 S) than Halicarcinus planatus (5-60 S); their respective lower and upper critical salinities are 4 and 12 S, and 63 and 50 S. Acanthocyclus albatrossis is a weak hyperosmotic regulator, while H. planatus hyperosmoconforms; isosmotic points are 1380 and â¼1340â mOsmâ kg-1 H2O, respectively. Both crabs hyper/hypo-regulate [Cl-] well with iso-chloride points at 452 and 316â mmolâ l-1 Cl-, respectively. [Na+] is hyper-regulated at all salinities. mRNA expression of gill Na+/K+-ATPase is salinity sensitive in A. albatrossis, increasing â¼1.9-fold at 5 compared with 30 S, decreasing at 40-60 S. Expression in H. planatus is very low salinity sensitive, increasing â¼4.7-fold over 30 S, but decreasing at 50 S. V-ATPase expression decreases in A. albatrossis at low and high salinities as in H. planatus. Na+/K+/2Cl- symporter expression in A. albatrossis increases 2.6-fold at 5 S, but decreases at 60 S versus 30 S. Chloride uptake may be mediated by increased Na+/K+/2Cl- expression but Cl- secretion is independent of symporter expression. These unrelated eubrachyurans exhibit similar systemic osmoregulatory characteristics and are better adapted to dilute media; however, the expression of genes underlying ion uptake and secretion shows marked interspecific divergence. Cold clime crabs may limit osmoregulatory energy expenditure by hyper/hypo-regulating hemolymph [Cl-] alone, apportioning resources for other energy-demanding processes.
Assuntos
Braquiúros , Simportadores , Cães , Animais , Braquiúros/metabolismo , Cloretos/metabolismo , Brânquias/metabolismo , ATPase Trocadora de Sódio-Potássio/metabolismo , Salinidade , Sódio/metabolismo , Simportadores/metabolismoRESUMO
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 Dilocarcinus pagei and the shrimp Macrobrachium jelskii, when osmotically challenged for up to 10â days. When in distilled water, D. pagei 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 M. jelskii, hemolymph osmolality, [Cl-] and [Na+] decreased continually for 12â h, the shrimps surviving only around 15-24â h exposure. Gill transporter gene expression increased 2- to 5-fold. After 10 days exposure to brackish water (25S), D. pagei 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 M. jelskii (20S), 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 D. pagei to survive in fresh water while V-ATPase, Na+/K+-ATPase and Na+/K+/2Cl- symporter expression enables M. jelskii to confront hyper/hypo-osmotic challenges. These findings reveal divergent responses in two unrelated crustaceans inhabiting a similar osmotic niche. While D. pagei does not secrete salt, tolerating elevated cellular isosmoticity, M. jelskii exhibits clear hypo-osmoregulatory ability. Each species has evolved distinct strategies at the transcriptional and systemic levels during its adaptation to fresh water.
Assuntos
Decápodes , Brânquias , Animais , Decápodes/genética , Decápodes/metabolismo , Água Doce , Expressão Gênica , Brânquias/metabolismo , Proteínas de Membrana Transportadoras , ATPase Trocadora de Sódio-Potássio/genética , ATPase Trocadora de Sódio-Potássio/metabolismoRESUMO
Intertidal pools are intensely challenging environments, due to rapid and extreme fluctuations in water conditions during the tidal cycle. Emersion is another challenge intertidal fishes may face. Mechanisms of ammonia excretion and ion regulation were studied in the resident amphibious blennid Lipophrys pholis. The ammonia transporters Rhcg1 and Rhcg2 were cloned and characterized. Fish were challenged for 24h to 1) emersion, 2) fresh water (FW), and 3) high environmental ammonia (HEA; 1mM NH4Cl), or 4) ammonia loading (1.5µmol/g NH4HCO3). When air exposed, L. pholis maintained aquatic ammonia excretion rates (JAmm) while branchial Na(+)/K(+)-ATPase (NKA) activity increased, but no changes at the protein or mRNA levels of transporters were noted. In FW, JAmm decreased and osmotic problems were encountered. Skin NKA activity decreased, branchial Rhcg2, and skin Rhcg1 and Rhcg2 increased. Exposure to HEA only increased branchial Rhcg2 levels. Although internal ammonia loading only led to a modest non-significant increase in JAmm, skin NKA (activity and α-subunit), carbonic anhydrase protein levels, and branchial Rhcg1 levels increased. In summary, variable responses were observed involving both gill and skin but given the instability of its habitat, the constitutive expression of transporters is likely also of importance.