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'.

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.

Daily variations of the antioxidant defense system of the lithodid crab Lithodes santolla.

Several physiological processes can induce daily variations in aerobic metabolism. Lithodes santolla is a decapod crustacean of special concern since it is a sub-Antarctic species of commercial interest. The aim of this work was to study in L. santolla the daily variations in levels of enzymatic and non-enzymatic antioxidants, lipid peroxidation and protein oxidation, and haemolymphatic pH. Males of L. santolla of commercial size were randomly dissected every 4 h during a period of 24 h. Enzymatic activities of superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase and glutathione peroxidase were determined in samples of gills, muscle, hepatopancreas and haemolymph. Ascorbic acid, total glutathione, lipid peroxidation and protein oxidation were also determined in all tissues. Gills showed the highest enzymatic activity and hepatopancreas the highest concentration of non-enzymatic antioxidants. Maximum antioxidant activity was during the dark phase in gills and during the photophase in the haemolymph. Muscle showed significant daily variations, with peaks during the photophase and scotophase. Overall, an antioxidant protective mechanism is present in all tissues, where SOD and CAT represent the first line of defense. The defense mechanism in L. santolla seems to be more active during the dark phase, with slight differences among the analyzed tissues, indicating a higher metabolic rate.

Living on the Edge: Physiological and Kinetic Trade-Offs Shape Thermal Tolerance in Intertidal Crabs From Tropical to Sub-Antarctic South America.

Temperature is an important abiotic factor that drives the evolution of ectotherms owing to its pervasive effects at all levels of organization. Although a species' thermal tolerance is environmentally driven within a spatial cline, it may be constrained over time due to differential phylogenetic inheritance. At the limits of thermal tolerance, hemolymph oxygen is reduced and lactate formation is increased due to mismatch between oxygen supply and demand; imbalance between enzyme flexibility/stability also impairs the ability to generate energy. Here, we characterized the effects of lower (LL50) and upper (UL50) critical thermal limits on selected descriptors of aerobic and anaerobic metabolism in 12 intertidal crab species distributed from northern Brazil (≈7.8°S) to southern Patagonia (≈53.2°S), considering their phylogeny. We tested for (i) functional trade-offs regarding aerobic and anaerobic metabolism and LDH kinetics in shaping thermal tolerance; (ii) influence of shared ancestry and thermal province on metabolic evolution; and (iii) presence of evolutionary convergences and adaptive peaks in the crab phylogeny. The tropical and subtropical species showed similar systemic and kinetic responses, both differing from the sub-Antarctic crabs. The lower UL50's of the sub-Antarctic crabs may reflect mismatch between the evolution of aerobic and anaerobic metabolism since these crabs exhibit lower oxygen consumption but higher lactate formation than tropical and subtropical species also at their respective UL50's. LDH activity increased with temperature increase, while Km Pyr remained fairly constant; catalytic coefficient correlated negatively with thermal niche. Thermal tolerance may rely on a putative evolutionary trade-off between aerobic and anaerobic metabolism regarding energy supply, while temperature compensation of kinetic performance is driven by thermal habitat as revealed by the LDH affinity/efficiency equilibrium. The overall physiological evolution revealed two homoplastic adaptive peaks in the sub-Antarctic crabs with a further shift in the tropical/subtropical clade. The physiological traits at UL50 have evolved in a phylogenetic manner while all others were more plastic. Thus, shared inheritance and thermal environment have driven the crabs' thermal tolerance and metabolic evolution, revealing physiological transformations that have arisen in both colder and warmer climes, especially at higher levels of biological organization and phylogenetic diversity.