Regulation of urine reprocessing in the maintenance of sodium and water balance in the terrestrial Christmas Island red crab Gecarcoidea natalis investigated under field conditions

Analysis of adaptive molecular mechanisms in response to low salinity in antennal gland of mud crab, Scylla paramamosain

As an important marine aquaculture species, the mud crab (Scylla paramamosain) is a good candidate for studying the osmoregulatory mechanism of crustaceans. While previous studies have focused on the osmoregulatory function of the gills, this study aims to explore the osmoregulatory function of the antennal glands. By the comparative transcriptomic analysis, we found the pathways of ion regulation including "proximal tubule bicarbonate reclamation" and "mineral absorption" were activated in the antennal glands of the crabs long-term dwelling in low salinity. The enhanced ionic reabsorption was associated with up-regulated ion transport genes such as NKA, CA-c, VPA, and NHE, and with energy metabolism genes such as MDH, SLC25, and PEPCK. The upregulation of NKA and CA-c was also verified by the increased enzyme activity. The lowered osmolality and ion concentration of the hemolymph and the enlarged labyrinth lumen and hemolymph capillary inside the antennal glands indicated the infiltration of external water and the responsively increase of urine excretion, which explained the requirement of enhanced ionic reabsorption. To further confirm these findings, we examined the change of gene expression, enzyme activity, internal ion concentration, and external ion concentration during a 96 h low salinity challenge with seven intervals. The results were basically consistent with the results as shown in the long-term low salinity adaptation. The present study provides valuable information on the osmoregulatory function of the antennal glands of S. paramamosain. The implication of this study in marine aquaculture is that it provides valuable information on the osmoregulatory mechanism of mud crabs, which can be used to improve their culture conditions and enhance their tolerance to salinity stress. The identified genes and pathways involved in osmoregulation can also be potential targets for genetic selection and breeding programs to develop more resilient mud crab strains for aquaculture.

A Multi-Species Comparison and Evolutionary Perspectives on Ion Regulation in the Antennal Gland of Brachyurans

Brachyurans inhabit a variety of habitats and have evolved diverse osmoregulatory patterns. Gills, antennal glands and a lung-like structure are important organs of crabs that maintain their homeostasis in different habitats. Species use different processes to regulate ions in the antennal gland, especially those with high terrestriality such as Grapsoidea and Ocypodoidea. Our phylogenetic generalized least square (PGLS) result also suggested that there is a correlation between antennal gland NKA activity and urine-hemolymph ratio for Na⁺ concentration in hypo-osmotic environments among crabs. Species with higher antennal gland NKA activity showed a lower urine-hemolymph ratio for Na⁺ concentration under hypo-osmotic stress. These phenomenon may correlate to the structural and functional differences in gills and lung-like structure among crabs. However, a limited number of studies have focused on the structural and functional differences in the antennal gland among brachyurans. Integrative and systemic methods like next generation sequencing and proteomics method can be useful for investigating the differences in multi-gene expression and sequences among species. These perspectives can be combined to further elucidate the phylogenetic history of crab antennal glands.

Making the grade: Physiological adaptations to terrestrial environments in decapod crabs

All extant macroscopic terrestrial diversity has evolved from the ancestors of a small group of successful terrestrial colonizers, but in a few lineages this transition has independently occurred multiple times in spite of the significant functional challenges it presents. Decapod crabs have transitioned from marine to terrestrial environments at least ten times, occupy diverse habitats, and display varying degrees of terrestriality. Previous attempts to categorize land crab diversity relied on single traits, did not explicitly distinguish between brachyuran and anomuran lineages, and did not separate lineages that colonized land via freshwater or marine environments. As a result, critical phylogenetic and ecological constraints were missing from these earlier classifications. In this paper, I reclassify terrestriality in the land crabs by designating four transition pathways that reflect deep phylogenetic relationships between the two decapod crab infraorders and the route-specific nature of this transition. I then describe the adaptive traits that evolved in response to six primary terrestrial selective challenges. I conclude by proposing six grades of terrestriality in this system that describe observable trait-by-environment associations, and propose studies that can test the hypothetical sequence of trait evolution and the nature of convergence in the land crabs using phylogenomic and transcriptomic tools.

Biochemical and metabolic responses of the deep-sea mussel Bathymodiolus platifrons to cadmium and copper exposure

Greater interest in commercial deep-sea mining has been accompanied by mounting environmental concerns, including metal contamination resulting from mining activities. However, little is known about the toxic effects of metal exposure on deep-sea life. Given its ability to accumulate metals from the surrounding environment, its wide distribution at both vents and seeps, and its high abundance, the deep-sea mussel Bathymodiolus platifrons could serve as an ideal model to investigate the toxicological responses of deep-sea organisms to metal exposure. Here, we evaluated metal accumulation, traditional metal-related biomarkers, namely acid phosphatase (ACP), alkaline phosphatase (AKP), superoxide dismutase, catalase, reduced glutathione, metallothioneins, and malondialdehyde, as well as metabolic profiles in the gills of B. platifrons after a 7-day exposure to copper (100 μg/L), cadmium (500 μg/L), or copper-plus-cadmium treatments (100 μg/L Cu and 500 μg/L Cd). Metal exposure concentrations selected in this study can be found in deep-sea hydrothermal environments. Metal exposure resulted in significant metal accumulation in the gills of the mussel, indicating that B. platifrons has promise for use as an indicator of deep-sea metal pollution levels. Traditional biomarkers (AKP, ACP, and measured antioxidants) revealed cellular injury and oxidative stress in mussels following metal exposure. Metabolic responses in the three treatment groups indicated that metal exposure perturbed osmoregulation, energy metabolism, and nucleotide metabolism in mussels, in a response marked by differentially altered levels of amino acids, hypotaurine, betaine, succinate, glucose 6-phosphate, fructose 6-phosphate, guanosine, guanosine 5'-monophosphate, and inosine. Nevertheless, several uniquely altered metabolites were found in each treatment exposure group, suggesting dissimilar modes of toxicity between the two metal types. In the Cd-exposed group, the monosaccharide D-allose, which is involved in suppressing mitochondrial ROS production, was downregulated, a response consistent with oxidative stress in Cd-exposed B. platifrons. In the Cu-exposed group, the detected alterations in dopamine, dopamine-related, and serotonin-related metabolites together suggest disturbed neurotransmission in Cu-exposed B. platifrons. In the Cu-plus-Cd group, we detected a decline in fatty acid levels, implying that exposure to both metals jointly exerted a negative influence on the physiological functioning of the mussel. To the best of our knowledge, this is the first study to investigate changes in metabolite profiles in Bathymodiolus mussels exposed to metal. The findings reported here advance our understanding of the adverse impact of metal exposure on deep-sea life and can inform deep-sea mining assessments through the use of multiple biomarkers.

Ion regulation in the antennal glands differs among Ocypodoidea and Grapsoidea crab species

Gills and the antennal gland are ion-regulatory organs in crabs. Previous studies have suggested that the differences in the morphology and ion regulation of gills and accessory respiratory organs between ocypodid and grapsid species are related to their distinct evolutionary transition to land habitats. In addition, Na⁺, K⁺-ATPase (NKA) activity and Na⁺ and NH₄⁺ regulation in the antennal gland differ between ocypodid and grapsid species, which had different terrestrial adaptation trajectories. This study used five Ocypodoidea species and three Grapsoidea species from the intertidal and supratidal zones to further investigate the differences in ion regulation and NKA activity in the antennal gland between these crab families in different habitats. Crabs were transferred to 5 practical salinity unit (PSU) water, and osmolality, Na⁺ and Cl^- concentrations in the urine and hemolymph, and NKA activity in the antennal gland were examined. Phylogenetic ANOVA results showed that the NKA activity in the antennal gland was higher in the ocypodid than grapsid groups, and Moran's I autocorrelation analysis also indicated that NKA activity in the antennal gland was phylogenetically correlated among crabs. K-means clustering showed a difference among the crabs in the crabs' Na⁺ and Cl^- concentrations in the urine/hemolymph, NKA activities in the antennal gland and gill 6, and number of pairs of gills. Crabs with relatively high antennal gland NKA activity were found not only in the Ocypode species, which are better adapted to terrestrial environments, but also in two intertidal species of Gelasiminae. In conclusion, part of the Ocypodidae lineage may have a) the ability to reabsorb Na⁺ and b) higher NKA activity in the antennal gland than other families, and this phenomenon is phylogenetically correlated in Ocypodoidea and Grapsoidea. The physiological diversity in osmoregulation among intertidal and costal species provides a base to further investigate their ecological niches and guilds.

Selective Amino Acid-Only in Vivo NMR: A Powerful Tool To Follow Stress Processes

In vivo NMR of small ¹³C-enriched aquatic organisms is developing as a powerful tool to detect and explain toxic stress at the biochemical level. Amino acids are a very important category of metabolites for stress detection as they are involved in the vast majority of stress response pathways. As such, they are a useful proxy for stress detection in general, which could then be a trigger for more in-depth analysis of the metabolome. ¹H-¹³C heteronuclear single quantum coherence (HSQC) is commonly used to provide additional spectral dispersion in vivo and permit metabolite assignment. While some amino acids can be assigned from HSQC, spectral overlap makes monitoring them in vivo challenging. Here, an experiment typically used to study protein structures is adapted for the selective detection of amino acids inside living Daphnia magna (water fleas). All 20 common amino acids can be selectively detected in both extracts and in vivo. By monitoring bisphenol-A exposure, the in vivo amino acid-only approach identified larger fluxes in a greater number of amino acids when compared to published works using extracts from whole organism homogenates. This suggests that amino acid-only NMR of living organisms may be a very sensitive tool in the detection of stress in vivo and is highly complementary to more traditional metabolomics-based methods. The ability of selective NMR experiments to help researchers to "look inside" living organisms and only detect specific molecules of interest is quite profound and paves the way for the future development of additional targeted experiments for in vivo research and monitoring.

(1)H NMR-based metabolomics of Daphnia magna responses after sub-lethal exposure to triclosan, carbamazepine and ibuprofen

Pharmaceuticals and personal care products are a class of emerging contaminants that are present in wastewater effluents, surface water, and groundwater around the world. There is a need to determine rapid and reliable bioindicators of exposure and the toxic mode of action of these contaminants to aquatic organisms. (1)H nuclear magnetic resonance (NMR)-based metabolomics in combination with multivariate statistical analysis was used to determine the metabolic profile of Daphnia magna after exposure to a range of sub-lethal concentrations of triclosan (6.25-100μg/L), carbamazepine (1.75-14mg/L) and ibuprofen (1.75-14mg/L) for 48h. Sub-lethal triclosan exposure suggested a general oxidative stress condition and the branched-chain amino acids, glutamine, glutamate, and methionine emerged as potential bioindicators. The aromatic amino acids, serine, glycine and alanine are potential bioindicators for sub-lethal carbamazepine exposure that may have altered energy metabolism. The potential bioindicators for sub-lethal ibuprofen exposure are serine, methionine, lysine, arginine and leucine, which showed a concentration-dependent response. The differences in the metabolic changes were related to the dissimilar modes of toxicity of triclosan, carbamazepine and ibuprofen. (1)H NMR-based metabolomics gave an improved understanding of how these emerging contaminants impact the keystone species D. magna.

Functional anatomy and ion regulatory mechanisms of the antennal gland in a semi-terrestrial crab, Ocypode stimpsoni

Brachyuran crabs from diverse habitats show great differences in their osmoregulatory processes, especially in terms of the structural and physiological characteristics of the osmoregulatory organs. In crustaceans, the antennal glands are known to be important in osmoregulation, and they play a functional role analogous to that of the vertebrate kidney. Nevertheless, the detailed structure and function of the antennal glands in different species have rarely been described. The aim of this study is to investigate the role of the antennal gland in ion regulation by examining the ultrastructure of the cells and the distribution of the ion regulatory proteins in each cell type in the antennal gland of a semi-terrestrial crab. The results showed that Na⁺, K⁺-ATPase activity significantly increased in the antennal gland after a 4-day acclimation in dilute seawater and returned to its original (day 0) level after 7 days. Three major types of cells were identified in the antennal gland, including coelomic cells (COEs), labyrinthine cells (LBRs) and end-labyrinthine cells (ELBRs). The proximal tubular region (PT) and distal tubular region (DT) of the antennal gland consist of LBRs and COEs, whereas the end tubular region (ET) consists of all three types of cells, with fewer COEs and more ELBRs. We found a non-uniform distribution of NKA immunoreactivity, with increasing intensity from the proximal to the distal regions of the antennal gland. We summarise our study with a proposed model for the urine reprocessing pathway and the role of each cell type or segment of the antennal gland.

Identification and developmental expression of the enzymes responsible for dopamine, histamine, octopamine and serotonin biosynthesis in the copepod crustacean Calanus finmarchicus

Neurochemicals are likely to play key roles in physiological/behavioral control in the copepod crustacean Calanus finmarchicus, the biomass dominant zooplankton for much of the North Atlantic Ocean. Previously, a de novo assembled transcriptome consisting of 206,041 unique sequences was used to characterize the peptidergic signaling systems of Calanus. Here, this assembly was mined for transcripts encoding enzymes involved in amine biosynthesis. Using known Drosophila melanogaster proteins as templates, transcripts encoding putative Calanus homologs of tryptophan-phenylalanine hydroxylase (dopamine, octopamine and serotonin biosynthesis), tyrosine hydroxylase (dopamine biosynthesis), DOPA decarboxylase (dopamine and serotonin biosynthesis), histidine decarboxylase (histamine biosynthesis), tyrosine decarboxylase (octopamine biosynthesis), tyramine β-hydroxylase (octopamine biosynthesis) and tryptophan hydroxylase (serotonin biosynthesis) were identified. Reverse BLAST and domain analyses show that the proteins deduced from these transcripts possess sequence homology to and the structural hallmarks of their respective enzyme families. Developmental profiling revealed a remarkably consistent pattern of expression for all transcripts, with the highest levels of expression typically seen in the early nauplius and early copepodite. These expression patterns suggest roles for amines during development, particularly in the metamorphic transitions from embryo to nauplius and from nauplius to copepodite. Taken collectively, the data presented here lay a strong foundation for future gene-based studies of aminergic signaling in this and other copepod species, in particular assessment of the roles they may play in developmental control.

(1)H NMR-based metabolomics investigation of Daphnia magna responses to sub-lethal exposure to arsenic, copper and lithium

Metal and metalloid contamination constitutes a major concern in aquatic ecosystems. Thus it is important to find rapid and reliable indicators of metal stress to aquatic organisms. In this study, we tested the use of (1)H nuclear magnetic resonance (NMR) - based metabolomics to examine the response of Daphnia magna neonates after a 48h exposure to sub-lethal concentrations of arsenic (49μgL(-1)), copper (12.4μgL(-1)) or lithium (1150μgL(-1)). Metabolomic responses for all conditions were compared to a control using principal component analysis (PCA) and metabolites that contributed to the variation between the exposures and the control condition were identified and quantified. The PCA showed that copper and lithium exposures result in statistically significant metabolite variations from the control. Contributing to this variation was a number of amino acids such as: phenylalanine, leucine, lysine, glutamine, glycine, alanine, methionine and glutamine as well as the nucleobase uracil and osmolyte glycerophosphocholine. The similarities in metabolome changes suggest that lithium has an analogous mode of toxicity to that of copper, and may be impairing energy production and ionoregulation. The PCA also showed that arsenic exposure resulted in a metabolic shift in comparison to the control population but this change was not statistically significant. However, significant changes in specific metabolites such as alanine and lysine were observed, suggesting that energy metabolism is indeed disrupted. This research demonstrates that (1)H NMR-based metabolomics is a viable platform for discerning metabolomic changes and mode of toxicity of D. magna in response to metal stressors in the environment.

Roles of crustacean hyperglycaemic hormone in ionic and metabolic homeostasis in the Christmas Island blue crab, Discoplax celeste

There is a growing body of evidence implicating the involvement of crustacean hyperglycaemic hormone (CHH) in ionic homeostasis in decapod crustaceans. However, little is known regarding hormonally influenced osmoregulatory processes in terrestrial decapods. As many terrestrial decapods experience opposing seasonal demands upon ionoregulatory physiologies, we reasoned that these would make interesting models in which to study the effect of CHH upon these phenomena. In particular, those (tropical) species that also undergo seasonal migrations might be especially informative, as we know relatively little regarding the nature of CHHs in terrestrial decapods, and hormonally mediated responses to seasonal changes in metabolic demands might also be superimposed or otherwise integrated with those associated with ionic homeostasis. Using Discoplax celeste as a model crab that experiences seasonal extremes in water availability, and exhibits diurnal and migratory activity patterns, we identified two CHHs in the sinus gland. We biochemically characterised (cDNA cloning) one CHH and functionally characterised (in terms of dose-dependent hyperglycaemic responses and glucose-dependent negative feedback loops) both CHHs. Whole-animal in situ branchial chamber (22)NaCl perfusion experiments showed that injection of both CHHs increased gill Na(+) uptake in a seasonally dependent manner, and (51)Cr-EDTA clearance experiments demonstrated that CHH increased urine production by the antennal gland. Seasonal and salinity-dependent differences in haemolymph CHH titre further implicated CHH in osmoregulatory processes. Intriguingly, CHH appeared to have no effect on gill Na(+)/K(+)-ATPase or V-ATPase activity, suggesting unknown mechanisms of this hormone's action on Na(+) transport across gill epithelia.

Crustacean neuroendocrine systems and their signaling agents

Decapod crustaceans have long served as important models for the study of neuroendocrine signaling. For example, the process of neurosecretion was first formally demonstrated by using a member of this order. In this review, the major decapod neuroendocrine organs are described, as are their phylogenetic conservation and neurochemistry. In addition, recent advances in crustacean neurohormone discovery and tissue mapping are discussed, as are several recent advances in our understanding of hormonal control in this group of animals.

Parasitic infection manipulates sodium regulation in the freshwater amphipod Gammarus pulex (L.)

The acanthocephalan parasite Polymorphus minutus induces both physiological and behavioural effects in its intermediate host, Gammarus pulex. The net effect of parasite infection is to increase the likelihood of transmission to the definitive host. Osmoregulation is an energetically expensive mechanism that allows G. pulex to survive in dilute media. Any factor influencing osmoregulation is thus likely to affect the allocation of resources to other areas. This study investigated whether P. minutus infection alters sodium regulation in G. pulex. Haemolymph sodium concentration, water permeability and sodium fluxes were measured over the salinity acclimation range of G. pulex. Water permeability was unaltered by either acclimation salinity or parasite infection. Acclimation to 12‰ significantly raised the haemolymph sodium concentration, reduced the sodium influx, and increased the sodium efflux, to the same extent in both uninfected and infected G. pulex. However, parasite infection induced a significant increase in haemolymph sodium concentration in G. pulex acclimated to 6‰, which was not observed in uninfected G. pulex acclimated to the same salinity. Also, both sodium influx and sodium efflux were significantly lower in parasitized G. pulex acclimated to 6‰, when compared to uninfected G. pulex acclimated to the same salinity. It was concluded that the parasite induced disturbances to sodium regulation in G. pulex acclimated to 6‰ were a functional consequence of the manipulative strategy employed to alter behaviour, rather than a primary target.

Ammonia excretion in aquatic and terrestrial crabs

The excretory transport of toxic ammonia across epithelia is not fully understood. This review presents data combined with models of ammonia excretion derived from studies on decapod crabs, with a view to providing new impetus to investigation of this essential issue. The majority of crabs preserve ammonotely regardless of their habitat, which varies from extreme hypersaline to freshwater aquatic environments, and ranges from transient air exposure to obligate air breathing. Important components in the excretory process are the Na+/K+(NH4+)-ATPase and other membrane-bound transport proteins identified in many species, an exocytotic ammonia excretion mechanism thought to function in gills of aquatic crabs such as Carcinus maenas, and gaseous ammonia release found in terrestrial crabs, such as Geograpsus grayi and Ocypode quadrata. In addition, this review presents evidence for a crustacean Rhesus-like protein that shows high homology to the human Rhesus-like ammonia transporter both in its amino acid sequence and in its predicted secondary structure.