Chronic Cadmium Exposure can Alter Energy Allocation to Physiological Functions in the Shrimp Penaeus vannamei.

Environmental stressors in aquatic organisms can be assessed using a bioenergetic approach based on the evaluation of changes in their physiological parameters. We evaluated the chronic effects of cadmium (Cd2+) on the energy balance as well as the survival, growth, metabolism, nitrogen excretion, hepatosomatic index, oxidized energy substrate, and osmoregulation of the shrimp Penaeus vannamei with the hypothesis that the high energy demand related to the homeostatic regulation of Cd2+could disrupt the energy balance and as a consequence, their physiological functions. The shrimp exposed to Cd2+ had higher mortality (30%), directed more energy into growth (33% of energy intake), ingested 10% more energy, and defecated less than control animals. Cd2+ exposure caused a tendency to decrease metabolism and ammonia excretion but did not alter the hepatosomatic index, type of energy substrate oxidized, and the hyperosmorregulatory pattern of the species. The Cd+2 exposure may have induced a trade-off response because there was a growth rate increase accompanied by increased mortality.

Effects of temperature increase on the physiology and behavior of fiddler crabs.

Intertidal organisms rely on physiological and behavioral adjustments to maintain homeostasis under warm exposure. We examined the effects of the temperature increase related to climate warming on the physiology and behavior of two fiddler crab species: Leptuca uruguayensis, which inhabits mostly vegetated areas, and Leptuca leptodactyla, that inhabits unvegetated areas. We hypothesized that L. uruguayensis would be more sensitive to warming than L. leptodactyla. Crabs were exposed to different temperatures: 27 °C (control), 31 and 33 °C (+4 and +6 °C, respectively) for 15 days to evaluate their physiological responses (oxygen consumption, Q10, ammonia excretion and hepatosomatic index) and for 2 days to observe their behavioral responses (feeding rate and duration of burrow retreat). We also tested in situ the effect of air, surface, and body temperatures on the claw-waving display of both species. We found that species were affected differently by increasing temperature. Leptuca uruguayensis showed adaptation limit (Q10 <1), increasing oxygen consumption. Also, in comparison with control, L. uruguayensis decreased the ammonia excretion at 31 °C, but not at 33 °C, indicating a compensatory mechanism to cope with thermal stress. In contrast, L. leptodactyla was able to adjust its metabolic rate to temperature rise (Q10 ~3) and reduce ammonia excretion, suggesting changes in the energetic substrate and amino acid catabolism. Higher temperatures reduce the hepatosomatic index of both species, indicating increased use of energy reserve (although only the L. uruguayensis feeding rate was reduced). Furthermore, warmer temperatures increase the duration of burrow retreat in both species, potentially impacting social interactions, such as mating. Temperature increase did not affect the claw-waving display frequency, suggesting that other factors may affect this behavior, e.g., the presence of females and competitors. Specific behavioral (e.g., microhabitat selection) and morphological attributes (e.g., larger major claw) might benefit the thermoregulation of each crab species since no differences in body temperature were found between them in situ. Therefore, fiddler crabs that inhabit vegetated areas are more vulnerable to higher temperatures and may change its geographic range as a result of climate warming, while fiddler crabs that inhabit unvegetated areas are more tolerant to temperature rise and may have a competitive advantage under a temperature increase scenario.

Point-of-care testing for measuring haemolymph glucose in invertebrates is not a valid method.

Blood glucose is widely used as a physiological parameter for vertebrates and invertebrates. However, its measurement in the field is often difficult due to the need for expensive and non-portable equipment. Point-of-care (POC) devices, originally intended for human use, are increasingly being used for measuring blood parameters of animals in the field. In this regard, POC glucose meters are becoming valuable tools for conservation physiologists, as glucose can be a useful indicator of stress response. In invertebrates, the use of POC glucose meters is still scarce, and no study yet has evaluated their usability in crustaceans and molluscs. We tested if a POC device can be used to measure haemolymph glucose in two widely used models, Leptuca thayeri and Perna perna, compared with a standard laboratory method. The device was unable to measure glucose in P. perna haemolymph due to equipment inaccuracy and low glucose concentration in this species (10.13 ± 6.25 mg/dL). Additionally, despite the device being capable of measuring glucose in L. thayeri haemolymph, Bland-Altman plots showed a strong bias and wide limits of agreement, and Lin's concordance correlation coefficient showed a weak concordance between methods. When simulating experimental conditions, POC results differed from those found using the standard method. We conclude that POC glucose meters are unsuitable for assessing glucose in mussels and should not be used in crabs as results are inaccurate.

Effects of ocean acidification and salinity variations on the physiology of osmoregulating and osmoconforming crustaceans.

Survival, osmoregulatory pattern, oxygen consumption, energy spent on metabolism, ammonia excretion, type of oxidized energy substrate, and hepatosomatic index were evaluated in decapods (an osmoregulating crab, Callinectes danae, and an osmoconforming seabob shrimp, Xiphopenaeus kroyeri) exposed to carbon dioxide-induced water acidification (pH 7.3, control pH 8.0) and different salinities (20, 25, 30, 35, and 40‰) for 3 days. Compared to the animals kept at controlled pH, exposure to reduced pH resulted in the loss of osmoregulatory capacity in C. danae at all salinities, except for some hyporegulation at 40‰, and reduced oxygen consumption and ammonia excretion at 20 and 40‰. Xiphopenaeus kroyeri remained an osmoconformer in all evaluated conditions, except for some hyporegulation at 40‰, and when exposed to the reduced pH, it presented changes in oxygen consumption at all salinities and reductions in ammonia excretion at 20 and 35‰ compared to the control animals. Both species use protein as the main energy substrate and decrease the hepatosomatic index when exposed to reduced pH relative to the control. The observed changes may be associated with changes in the activity of enzymes related to osmoregulation, the use of amino acids as osmotic effectors of cell volume control and recovery, and the Bohr effect, and, because the gills are multifunctional organs related to osmoregulation, the changes may be related to acid-base control, nitrogen excretion, and respiration, with a change in one of these functions bringing about changes in the others.

Differential effects of water loss and temperature increase on the physiology of fiddler crabs from distinct habitats.

Temperature is one of the main environmental constraints to organism distribution, affecting physiology and survival. Organisms that inhabit the intertidal zone are exposed to temperature variation and, with climate change, they should face different conditions which include higher temperatures, leading to higher rates of water loss through evaporation and then fitness reduction or mortality. Here we tested the effects of desiccation and increased temperature in two fiddler crabs species that occupy distinct habitats in regard to vegetation cover and position on the intertidal zone and thus may respond differently to these stressors. Leptuca thayeri, which is restricted to the mid-tide zone and vegetated areas, had higher desiccation and mortality rates than Minuca rapax, a generalist species, when exposed to desiccation for 120 min. Also, compared to M. rapax, L. thayeri had a more permeable carapace. Temperature elevation of 10 °C and 20 °C for 72 h caused no mortality in either species. However, there were changes in hemolymph osmolality and muscle hydration in both species. Leptuca thayeri osmolality was low in the intermediate temperature, suggesting that at this temperature this species has a better salt secretion capability. Minuca rapax, however, had an increase in hemolymph osmolality at the highest temperatures with no LDH increase, which indicates that osmotic control in this species is more sensitive to temperature increase. Our results show that L. thayeri suffers more from desiccation, due to a more permeable carapace. However, because of this higher permeability L. thayeri is capable of lowering its temperature more than M. rapax. As temperature elevation produces great physiological changes in M. rapax, a reduced ability to keep a low temperature can be an issue for this species if temperature increases. However, higher water loss to keep body temperature low may decrease L. thayeri survivability in the same scenario.

Kinetic analysis of gill (Na⁺,K⁺)-ATPase activity in selected ontogenetic stages of the Amazon River shrimp, Macrobrachium amazonicum (Decapoda, Palaemonidae): interactions at ATP- and cation-binding sites.

We investigated modulation by ATP, Mg²âº, Na⁺, K⁺ and NH4⁺ and inhibition by ouabain of (Na⁺,K⁺)-ATPase activity in microsomal homogenates of whole zoeae I and decapodid III (formerly zoea IX) and whole-body and gill homogenates of juvenile and adult Amazon River shrimps, Macrobrachium amazonicum. (Na⁺,K⁺)-ATPase-specific activity was increased twofold in decapodid III compared to zoea I, juveniles and adults, suggesting an important role in this ontogenetic stage. The apparent affinity for ATP (K(M) = 0.09 ± 0.01 mmol L⁻¹) of the decapodid III (Na⁺,K⁺)-ATPase, about twofold greater than the other stages, further highlights this relevance. Modulation of (Na⁺,K⁺-ATPase activity by K⁺ also revealed a threefold greater affinity for K⁺ (K0.5 = 0.91 ± 0.04 mmol L⁻¹) in decapodid III than in other stages; NH4⁺ had no modulatory effect. The affinity for Na⁺ (K0.5 = 13.2 ± 0.6 mmol L⁻¹) of zoea I (Na⁺,K⁺)-ATPase was fourfold less than other stages. Modulation by Na⁺, Mg²âº and NH4⁺ obeyed cooperative kinetics, while K⁺ modulation exhibited Michaelis-Menten behavior. Rates of maximal Mg²âº stimulation of ouabain-insensitive ATPase activity differed in each ontogenetic stage, suggesting that Mg²âº-stimulated ATPases other than (Na⁺,K⁺)-ATPase are present. Ouabain inhibition suggests that, among the various ATPase activities present in the different stages, Na⁺-ATPase may be involved in the ontogeny of osmoregulation in larval M. amazonicum. The NH4⁺-stimulated, ouabain-insensitive ATPase activity seen in zoea I and decapodid III may reflect a stage-specific means of ammonia excretion since functional gills are absent in the early larval stages.

Intra- and extracellular osmotic regulation in the hololimnetic Caridea and Anomura: a phylogenetic perspective on the conquest of fresh water by the decapod Crustacea.

We investigate extra- and intracellular osmoregulatory capability in two species of hololimnetic Caridea and Anomura: Macrobrachium brasiliense, a palaemonid shrimp, and Aegla franca, an aeglid anomuran, both restricted to continental waters. We also appraise the sharing of physiological characteristics by the hololimnetic Decapoda, and their origins and role in the conquest of fresh water. Both species survive salinity exposure well. While overall hyperosmoregulatory capability is weak in A. franca and moderate in M. brasiliense, both species strongly hyporegulate hemolymph [Cl(-)] but not osmolality. Muscle total free amino acids (FAA) increase slowly but markedly in response to the rapid rise in hemolymph osmolality consequent to hyperosmotic challenge: 3.5-fold in A. franca and 1.9-fold in M. brasiliense. Glycine, taurine, arginine, alanine and proline constitute ≈85% of muscle FAA pools in fresh water; taurine, arginine, alanine each contribute ≈22% in A. franca, while glycine predominates (70%) in M. brasiliense. These FAA also show the greatest increases on salinity challenge. Muscle FAA titers correlate strongly (R = 0.82) with hemolymph osmolalities across the main decapod sub/infraorders, revealing that marine species with high hemolymph osmolalities achieve isosmoticity of the intra- and extracellular fluids partly through elevated intracellular FAA concentrations; freshwater species show low hemolymph osmolalities and exhibit reduced intracellular FAA titers, consistent with isosmoticity at a far lower external osmolality. Given the decapod phylogeny adopted here and their multiple, independent invasions of fresh water, particularly by the Caridea and Anomura, our findings suggest that homoplastic strategies underlie osmotic and ionic homeostasis in the extant freshwater Decapoda.

Adaptive shifts in osmoregulatory strategy and the invasion of freshwater by brachyuran crabs: evidence from Dilocarcinus pagei (Trichodactylidae).

To evaluate putative adaptive changes underpinning the invasion of freshwater by the Brachyura, this investigation examines anisosmotic extra and isosmotic intracellular osmoregulatory capabilities in Dilocarcinus pagei, a neotropical, hololimnetic crab, including its embryonic and juvenile phases. All ontogenetic stages show a remarkable ability to survive a high salinity medium (25 per thousand, 750 mOsm/kg H2O, 350 mm Na+, 400 mM Cl-). Adults hyper-regulate hemolymph osmolality up to isosmoticity at 744 mOsm kg/H2O (24 per thousand), [Na+] and [Cl-] becoming isoionic at 449 (22 per thousand) and 256 mM (16 per thousand), respectively. Hemolymph (420+/-39 mOsm/kg H2O) and urine (384+/-44 mOsm/kg H2O) are isosmotic in adults held in freshwater, and after 5-days exposure to 25 per thousand (787+/-9 mOsm/kg H2O and 777+/-43 mOs/kg H2O, respectively); D. pagei does not produce dilute urine. Total free amino acid (FAA) concentrations in embryos (14.9+/-1.2), juveniles (32.8+/-0.1) and adult muscle (10.9+/-2.1 mmol/kg wet weight) in freshwater are 30-fold less than in brackish/marine Crustacea, suggesting that FAA constitute a useful parameter to evaluate adaptation to freshwater. On acclimation to 25 per thousand, total FAA increase by approximately 100% in embryos and in adult muscle and nerve tissue and hemolymph, owing to large increases in proline, arginine and/or alanine. However, effective FAA contribution to intracellular osmolality increases only in embryos, from 3 to 4.5%. These findings suggest that gill-based, anisosmotic extracellular regulation has supplanted isosmotic intracellular regulatory mechanisms during the conquest of freshwater by the Brachyura, and indicate that D. pagei may be an old, well-adapted inhabitant of this biotope.