Evolutionary trade-offs in osmotic and ionic regulation and expression of gill ion transporter genes in high latitude, cold clime Neotropical crabs from the ‘end of the world’

MCNAMARA, JOHN CAMPBELL; MARASCHI, ANIELI CRISTINA; TAPELLA, FEDERICO; ROMERO, MARIA CAROLINA

JOURNAL OF EXPERIMENTAL BIOLOGY

COMPANY OF BIOLOGISTS LTD

Año: 2023 vol. 226

0022-0949

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 ∼1340 mOsm kg−1 H2O, respectively. Both crabs hyper/hypo-regulate [Cl−] well with iso-chloride points at 452 and 316 mmol 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 ∼1.9-fold at 5‰ compared with 30‰ S, decreasing at 40–60‰ S. Expression in H. planatus is very low salinity sensitive, increasing ∼4.7-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.