The role of ion regulation in the control of the distribution of Gammarus tigrinus (Sexton) in salt-polluted rivers

Fluctuating salinities at different sites on the German salt-polluted rivers Werra and Weser were compared with extracellular ion levels of specimens of Gammarus tigrinus (Sexton; Amphipoda, Crustacea), collected at the same sites. G. tigrinus regulated haemolymph concentrations of inorganic anions (Cl⁻, SO²⁻ ₄, PO³⁻ ₄) and cations (Na⁺, K⁺, Mg²⁺, Ca²⁺) during fluctuations of salt pollution in the upper Weser. This capacity to regulate varying levels of salt pollution in the upper Weser, correlated well with the distribution of the brackish amphipods in this river ecosystem. G. tigrinus tolerated periods of Na⁺ and Cl⁻ stress (>380 mmol l⁻¹) without compensating these maxima by regulating extracellular Na⁺ and Cl⁻. However, during such bursts of Na⁺ and Cl⁻ stress in Werra and Weser, the ability to regulate extracellular [K⁺] at river water K⁺ stress of ≥6.0 mmol l⁻¹ may explain why this brackish species has been more successful in these rivers than its competitors like Gammarus pulex. The present investigation demonstrates that the water salinity affects the [NO⁻ ₃] in the haemolymph of G. tigrinus. With increasing hypo-osmotic stress the animals accumulate increasing amounts of NO⁻ ₃. A simultaneous increase in stream water [NO⁻ ₃] causes an additional accumulation of NO⁻ ₃ in the haemolymph. The high extent of accumulation indicates that active ion transport systems may be involved. The accumulation of NO⁻ ₃ in the haemolymph has low physiological consequences to G. tigrinus, but when hypo-osmotically stressed under anoxic conditions, nitrite formed by the reduction of nitrate may have an adverse affect on the metabolism of G. tigrinus. Accepted: 4 October 1999     

Influence of long-term hypoxia on the energy metabolism of the haemoglobin-containing bivalve Scapharca inaequivalvis: critical O2 levels for metabolic depression

Summary The oxygen consumption rate of Scapharca inaequivalvis measured under normoxic conditions over 48 h showed a significant daily cycle with lowest values occurring shortly after the dark period; all hypoxia exposure experiments were carried out during the declining part of the cycle. Animals were exposed to a constant level of hypoxia for a 12-h period in a series of 14 experiments, each at a different oxygen tension. The oxygen consumption was measured continuously, and the extent of accumulation of end-products (succinate and propionate), and the inhibitory effect of adenosine triphosphate on phosphofructokinase were determined at the end of exposures. All three parameters (oxygen consumption, end-product accumulation, phosphofructokinase inhibition) showed a remarkable correlation with major changes occurring between 2.5 and 1.5 ppm (7 and 4 kPa) O₂. The oxygen consumption rates showed a drop to 6% of the normoxic rate, but a consistent low consumption remained below 2 ppm (5.5 kPa) which partly recovered over the 12-h exposure period by about three-fold. Succinate and propionate accumulated progressively between 2.5 and 1.5 ppm (7 and 4 kPa); at [O₂]<1.5 ppm (4kPa) the concentration did not increase further, indicating that anaerobic metabolism had reached a maximum. Over the same range, phosphofructokinase showed an increased sensitivity for adenosine triphosphate, the lower inhibitor concentration at 50% V _max value pointing to depression of glycolytic rate. Despite the activation of anaerobic metabolism and the evident depression of aerobic metabolism, simple calculation demonstrates that Scapharca inaequivalvis relies mainly on aerobic metabolism even during severe hypoxia. It is assumed that the occurrence of haemoglobin in this species is essential for its capacity to survive long periods of hypoxia.Abbreviations ATP adenosine triphosphate - I₅₀ inhibitor concentration at 50% V _max - PFK phosphofructokinase - P _c critical PO₂ - SEM standard error of mean - VO₂ oxygen consumption rate - ww wet weight     

Recovery after anaerobic metabolism in the leech (Hirudo medicinalis L.)

Medicinal leeches (Hirudo medicinalis L.) responded to self-induced hypoxia (72 h) with typical anaerobic metabolism characterized by a decrease in adenylate energy charge, utilization of the substrates glycogen and malate, and accumulation of the main anaerobic endproducts succinate and propionate. Propionate was also excreted into the medium. Ammonia excretion was suppressed. Aerobic recovery resulted in a profound O₂ debt. Resynthesis of ATP was completed within 30 min. Disposal of succinate and restoring of malate required 2–3 h, and clearance of propionate and recharging of glycogen 6–12 h. Ammonia excretion did not exceed normoxic rates and excretion of propionate during recovery accounted for only 10% of total propionate accumulated during hypoxia. It is postulated that the clearance of succinate and propionate involves oxidation but also resynthesis of malate and glycogen. During hypoxia and recovery blood osmolality remained constant. The Na⁺ and Cl^- ion concentrations in blood, the decrease of which was nearly equimolar during hypoxia, were re-established following different time-courses. Na⁺ concentration returned to normoxic levels after 2–3 h. The delayed increase in Cl^- concentration, however, correlating with 6–12 h necessary to clear blood propionate, is interpretated as an anion regulating effect.Abbreviations AEC adenylate energy charge; fw, fresh weight - HPLC high-performance liquid chromatography - SCCA shortchain carboxylic acids     

The influence of oxygen deficiency on ethylene synthesis, 1-aminocyclopropane-1-carboxylic acid levels and aerenchyma formation in roots of Zea mays

The relationship between ethylene production, 1-aminocyclopropane-l-carboxylic acid (ACC) concentration and aerenchyma formation (ethylene-promoted cavitation of the cortex) was studied using nodal roots of maize (Zea mays L. cv. LG11) subjected to various O₂ treatments. Ethylene evolution was 7–8 fold faster in roots grown at 3 kPa O₂ than in those from aerated solution (21 kPa O₂), and transferring roots from aerated solution to 3 kPa O₂ enhanced ethylene synthesis within less than 2 h. Ethylene production and ACC accumulation were closely correlated in different zones of hypoxic roots, regardless of whether O₂ was furnished to the roots through aerenchyma or external solution. Both ethylene production and ACC concentrations (fresh weight basis) were more than 10-fold greater in the distal 0–10 mm than in the fully expanded zone of roots at 3 kPa O₂. Aerenchyma formation occurred in the apical 20 mm of these roots. Roots transferred from air to anoxia accumulated less than 0. 1 nmol ACC (mg protein)^-1 for the first 1.75 h; no ethylene was produced in this time. The subsequent rise in ACC levels shows that ACC can reach high concentrations even in the absence of O₂, presumably due to a de-repression of ACC synthase. The hypothesis was therefore tested that anoxia in the apical region of the root caused enhanced synthesis of ACC, which was transported to more mature regions (10–20 mm behind the apex), where ethylene could be produced and aerenchyma formation stimulated. Surprisingly, exposure of intact root tips to anoxia inhibited aerenchyma formation in the mature root axis. High osmotic pressures around the growing region or excision of apices had the same effect, demonstrating that a growing apex is required for high rates of aerenchyma formation in the adjacent tissue.     

Respiratory responses and tolerance to hypoxia in two marine teleosts,Epinephelus akaara (Temminck & Schlegel) and Mylio macrocephalus (Basilewsky)

The respiratory responses and tolerance of hypoxia were studied in two marine teleosts, the red grouper (Epinephelus akaara, a sluggish species) and the black sea bream (Mylio macrocephalus, an active species). Neither species showed abnormal behaviour or mortality when exposed to 2 mg O₂ l^–1 for 7 h. The black sea bream was, however, comparatively more tolerant when exposed to 1 mg O₂ l^–1, but tolerance of both species became similar under extremely hypoxic conditions (i.e. 0.5 mg O₂ l^–1). In contrast to most other teleosts, both species showed a reduction in opercular beating rate during hypoxia, and oxygen conformity was found in the range of 0.5 to 7.0 mg O₂l ^–1. O₂ dissociation curves were constructed, and the P₅₀ value of the black sea breams (27 ± 5.6 mm Hg) was found to be much lower than that of the red groupers (50 ± 2.5 mm Hg). For both species, the general levels of venous PO₂ showed a direct relationship to ambient PO₂, and were markedly reduced after 1 h exposure to various levels of hypoxia. Compared with the red groupers, the black sea breams appeared to be more able to maintain its venous PO₂ levels during prolonged hypoxic exposure.     

Continuous measurement of oxygen tensions in the air-breathing organ of Pacific tarpon (Megalops cyprinoides) in relation to aquatic hypoxia and exercise

The Pacific tarpon is an elopomorph teleost fish with an air-breathing organ (ABO) derived from a physostomous gas bladder. Oxygen partial pressure (PO₂) in the ABO was measured on juveniles (238 g) with fiber-optic sensors during exposure to selected aquatic PO₂ and swimming speeds. At slow speed (0.65 BL s⁻¹), progressive aquatic hypoxia triggered the first breath at a mean PO₂ of 8.3 kPa. Below this, opercular movements declined sharply and visibly ceased in most fish below 6 kPa. At aquatic PO₂ of 6.1 kPa and swimming slowly, mean air-breathing frequency was 0.73 min⁻¹, ABO PO₂ was 10.9 kPa, breath volume was 23.8 ml kg⁻¹, rate of oxygen uptake from the ABO was 1.19 ml kg⁻¹ min⁻¹, and oxygen uptake per breath was 2.32 ml kg⁻¹. At the fastest experimental speed (2.4 BL s⁻¹) at 6.1 kPa, ABO oxygen uptake increased to about 1.90 ml kg⁻¹ min⁻¹, through a variable combination of breathing frequency and oxygen uptake per breath. In normoxic water, tarpon rarely breathed air and apparently closed down ABO perfusion, indicated by a drop in ABO oxygen uptake rate to about 1% of that in hypoxic water. This occurred at a wide range of ABO PO₂ (1.7–26.4 kPa), suggesting that oxygen level in the ABO was not regulated by intrinsic receptors.     

Acclimatory responses of the Daphnia pulex proteome to environmental changes. I. Chronic exposure to hypoxia affects the oxygen transport system and carbohydrate metabolism

Background  

Freshwater planktonic crustaceans of the genus Daphnia show a remarkable plasticity to cope with environmental changes in oxygen concentration and temperature. One of the key proteins of adaptive gene control in Daphnia pulex under hypoxia is hemoglobin (Hb), which increases in hemolymph concentration by an order of magnitude and shows an enhanced oxygen affinity due to changes in subunit composition. To explore the full spectrum of adaptive protein expression in response to low-oxygen conditions, two-dimensional gel electrophoresis and mass spectrometry were used to analyze the proteome composition of animals acclimated to normoxia (oxygen partial pressure [Po₂]: 20 kPa) and hypoxia (Po₂: 3 kPa), respectively.     

Effect of zinc on four populations and two generations of Gammarus pulex (L.)

1. The amphipod Gammarus pulex (L.) is increasingly used in toxicity assessments and is usually obtained from wild populations. Interpopulation variability in response to toxicants may be due to genetic or phenotypic differences and could be large in wild-caught organisms exposed to different environmental conditions. This paper describes an investigation designed to assess the extent of lethal and sublethal variability between four different G. pulex populations when exposed to zinc, and to determine whether differences observed in the parental generation were also apparent in offspring bred in the laboratory. 2. The mortality of G. pulex from one of the four field-caught populations (Crags Stream) was significantly lower than for animals from the other three populations for the first 2 days of exposure. After 6 days’ exposure the LC₅₀ values for all four populations did not differ significantly, and were approximately 1.0 mg Zn 1-^?1. Sublethal effects on feeding rate after 6 days’ exposure were also similar for all four populations (feeding rate EC₅₀ approximately 0.5 mg Zn 1-^?1). 3. Lethal effects on the F₁ generation were similar among the four populations, in contrast to the short-term differences observed in the parental generation. These results suggest that interpopulation differences in zinc tolerance in G. pulex are short-lived, and phenotypically rather than genetically based.     

Production of Gammarus pulex L. (Amphipoda) in a small Danish stream

Quantitative samples of Gammarus pulex L. taken from a small Danish stream during 1975 showed mean annual population densities varying from 500 m^–2 in early May to 5 500 m^–2 in late September. The mean annual biomass was 1.5 g dry weight m^–2. No discrete cohorts could be distinguished from the size frequency distributions. Annual production, estimated by the size-frequency method, was 3.9 g dry weight M^-2 and P/B ratio was 2.6. The contribution to trout energetics may have been as much as 17%.     

Acute and Sub-lethal Toxicity of Landfill Leachate Towards Two Aquatic Macro-invertebrates: Demonstrating the Remediation Potential of Aerobic Digestion

A specific landfill leachate that contained 1.036 mgl⁻¹of 2-chlorobiphenyl was used in the study (255 mg l⁻¹ COD and 133 mg l⁻¹ BOD₅). Three, 2-l semi-continuous batch reactors (SBRs) were used to simulate the treatment potential of this method on a small scale. Aerobic digestion effectively reduced the leachates COD concentration. Regardless of dilution, the leachates COD reached a <20 mg l⁻¹ equilibrium after 96 h exposure to aerobic digestion, however, increasing the level of dilution accelerated the process. In untreated leachate, the LC₅₀ for Asellus aquaticus was 57% v/v leachate in deionised water and 5% for Gammarus pulex (96 h, static LC₅₀ tests without nutrition and oxygen depleting conditions). After being exposed to aerobic digestion, these values rose to 95% and 40%, respectively. Prolonged exposure to a 1:20 sub-lethal dilution of the aforementioned leachate has been previously shown to affect the breeding colony size of Asellus aquaticus and a 1:66 dilution influenced the fecundity of a Gammarus pulex population. After remediation by aerobic digestion, however, the population dynamics of both test species remained unaltered.     

Physiological reactions of aquatic oligochaetes to environmental anoxia

Aquatic oligochaetes are well known for their ability to resist prolonged periods of anoxia. In fact, the observed mortality is more likely to result from laboratory stress (unnatural sediment, starvation, accumulation of toxic substances) than from lack of oxygen per se. Lumbriculus variegatus feeds under anoxia at 6°C at a low rate and survives more than 40 days. A sudden transfer into anoxic water, however, results in a cessation of defaecation before the gut is half emptied, whereas the gut is completely emptied under aerobic conditions within 8–10 hours (11°C).Anoxic heat dissipation as measured by direct calorimetry is reduced by up to 80% relative to aerobic rates. The basal rate of oxygen uptake is independent of PO₂ above 3 kPa (15% air saturation), but the active rate shows a high degree of oxygen conformity. Whereas the theoretical oxycaloric equivalent yields an accurate estimation of aerobic heat dissipation in Lumbriculus, anoxic catabolism of glycogen explains only up to 60% of the directly measured rates of anoxic heat dissipation in Lumbriculus and Tubifex. Since unknown bioenergetic processes may be important under anoxia, direct calorimetry is required to assess total rates of energy expenditure in anoxic oligochaetes.     

Respiratory Levels and Adaptations in Four Freshwater Species of Gammarus (Crustacea: Amphipoda)

Respiration of four freshwater species of the amphipod crustacean Gammarus: G. fossarum, G. lacustris (river and lake), G. pulex and G. roeseli were measured in a closed, stirred respirometric chamber with a micro-electrode. Oxygen consumption, expressed as weight-specific oxygen uptake (R_s) in relation to decreasing oxygen concentration, varied at air saturation from 0.86 (G. lacustris, lake) to 2.06 μl O₂ mg⁻¹ AFDW h⁻¹ (G. pulex). R_s also differed intra-specifically among the two populations of G. lacustris. G. lacustris (river), G. pulex and G. roeseli expressed moderate ability to regulate their oxygen consumption at decreasing oxygen concentrations, whereas the regulation ability was higher in G. lacustris (lake) and in G. fossarum, which maintain high oxygen uptake at oxygen levels >2 mg O₂ l⁻¹. All four Gammarus species are partial regulators in response to variations in oxygen concentration. The differences between species are considered too small to account for their natural distributions. It appears that the tolerances of Gammarus species to organic pollution depend only in part on oxygen conditions.     

Anaerobic metabolism in aquatic insect larvae: studies onChironomus thummi andCulex pipiens

Summary The metabolic effect of hypoxia and anoxia on the larvae ofChironomus thummi andCulex pipiens was investigated. InC. thummi anoxia resulted in a characteristic decrease of ATP and P-arginine concentrations and in an accumulation of alanine and lactate within 60 minutes. These changes continued during prolonged incubation but at lower rates. Ethanol, the major product during long-term anoxia, was largely excreted into the ambient water.A significant accumulation of these metabolites occurred only at a of 7 Torr. However, the proportion of anaerobic energy production even at this low amounted to less than 5% of the total energy consumption measured during experimental anoxia. Thus the chironomid larvae exhibited a remarkable capacity for utilizing very low levels of oxygen to maintain an aerobic metabolism. Complete anaerobiosis was observed only under anoxic conditions.Recovery from prior anoxia began with the reestablishment of normal ATP, P-arginine and succinate concentrations, whereas removal of the accumulated alanine and lactate and replenishment of the normally high level of malate required several hours. Culex larvae were shown to have a very low anaerobic capacity and a high rate of lactate accumulation.The significance of the results is discussed with particular emphasis on comparative aspects.     

Contribution a l'etude de l'accumulation et de la toxicite de l'etain et du plomb chez des crustaces gammaridet

Résumé Nous avons étudiés les effets toxiques de l'accumulation de l'étain et du plomb sur les G. pulex d'eau douce et les G. locusta (Crustacés: Amphipodes) marin.Les expériences ont été faites dans des solutions de métaux d'eau douce et d'eau marine. Les concentrations de métal utilisées sont de 10 ppm, de 1 ppm et de 0.1 ppm. Les résultats nous ont montrés que les solutions de plomb sont plus toxique que les solutions de l'étain et les G. locusta sont plus sensibles que les G. pulex.Les valeurs de l'accumulation de métal ont été determinées par spectrographie des rayons X. Pour les deux espèces, une grande accumulation d'étain a été rencontrée dans le système digestif, la cuticule et l'hemolymphe et une accumulation de plomb a été rencontré dans le système digestif et la cuticule.

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The effects of tin (SnCl₄.5H₂O) and lead [Pb(NO₃)₂] on Gammarus pulex (L.) and Gammarus locusta (L.) have been studied. Three differents solutions (10 ppm, 1 ppm, 0.1 ppm) were applied for two metals. Lead was found to be more toxic than tin. The residues of metals in the organes and tissues of two species were determined by X ray spectrophotometry.

     

Oxygen as a driver of early arthropod micro-benthos evolution

Background

We examine the physiological and lifestyle adaptations which facilitated the emergence of ostracods as the numerically dominant Phanerozoic bivalve arthropod micro-benthos.

Methodology/Principal Findings

The PO₂ of modern normoxic seawater is 21 kPa (air-equilibrated water), a level that would cause cellular damage if found in the tissues of ostracods and much other marine fauna. The PO₂ of most aquatic breathers at the cellular level is much lower, between 1 and 3 kPa. Ostracods avoid oxygen toxicity by migrating to waters which are hypoxic, or by developing metabolisms which generate high consumption of O₂. Interrogation of the Cambrian record of bivalve arthropod micro-benthos suggests a strong control on ecosystem evolution exerted by changing seawater O₂ levels. The PO₂ of air-equilibrated Cambrian-seawater is predicted to have varied between 10 and 30 kPa. Three groups of marine shelf-dwelling bivalve arthropods adopted different responses to Cambrian seawater O₂. Bradoriida evolved cardiovascular systems that favoured colonization of oxygenated marine waters. Their biodiversity declined during intervals associated with black shale deposition and marine shelf anoxia and their diversity may also have been curtailed by elevated late Cambrian (Furongian) oxygen-levels that increased the PO₂ gradient between seawater and bradoriid tissues. Phosphatocopida responded to Cambrian anoxia differently, reaching their peak during widespread seabed dysoxia of the SPICE event. They lacked a cardiovascular system and appear to have been adapted to seawater hypoxia. As latest Cambrian marine shelf waters became well oxygenated, phosphatocopids went extinct. Changing seawater oxygen-levels and the demise of much of the seabed bradoriid micro-benthos favoured a third group of arthropod micro-benthos, the ostracods. These animals adopted lifestyles that made them tolerant of changes in seawater O₂. Ostracods became the numerically dominant arthropod micro-benthos of the Phanerozoic.

Conclusions/Significance

Our work has implications from an evolutionary context for understanding how oxygen-level in marine ecosystems drives behaviour.     

Respiratory and metabolic responses of the Australian Yabby Cherax destructor to progressive and sustained environmental hypoxia

The Australian Yabby, Cherax destructor, inhabits occasionally hypoxic water. The respiratory gas, acid-base, metabolite and energetic status of this crayfish was assessed during progressive hypoxia and during 3 h at a water PO₂ of 1.33 kPa. The O₂ affinity of haemocyanin from C. destructor was increased by lactate (Δlog P ₅₀/Δlog[lactate] = −0.111) and by Ca (Δlog P ₅₀/Δlog[Ca] = −0.62) but not by urate. While the non-bicarbonate buffering capacity was low (Δ[HCO₃ ⁻]/ ΔpH=−4.89) the haemocyanin had a low sensitivity to pH changes (ϕ = −0.33). The crayfish showed a compensatory hyperventilation, which induced a respiratory alkalosis, until the water O₂ partial pressure declined below 2.67 kPa, after which the O₂ uptake rate was approximately 10% of normoxic rates. The high haemocyanin-O₂ affinity maintained haemolymph O₂ content during progressive hypoxia despite the normally low arterial O₂ partial pressure of C. destructor. During severe hypoxia, pH decreased but increased lactate aided in maintaining haemocyanin-O₂ saturation. The importance of regulated haemocyanin-O₂ affinity in hypoxic C. destructor was reduced by lowered metabolism, including reduced cardiac output, and the consequent reduction in O₂ requirement. Anaerobiosis became important only at very low PO₂ but thereafter proceeded rapidly, supported by a marked hyperglycaemia. There was no depletion of adenylates, even after 3 h of severe hypoxia. The tail muscle of C. destructor held small amounts of glycogen which would sustain anaerobiosis for a only a few hours. Hypometabolism seems an important hypoxic response but severe hypoxia may encourage the crayfish to breathe air. Accepted: 26 February 1998     

On the Physiological Role of Anaerobically Synthesized Lipids in <Emphasis Type="Italic">Oryza sativa</Emphasis> Seedlings

The objective of this work was to elucidate a possible adaptive role of lipid biosynthesis and unsaturated fatty acids (FAs), esterified to lipids, as terminal acceptors of electrons, alternative to molecular oxygen, in the shoots of rice seedlings (Oryza sativa L.) under conditions of strict anoxia. Biosynthesis of lipids and their accumulation, as well as the reduction of double bonds in unsaturated FAs, were studied by electron microscopic observation of the accumulation of lipid bodies in the cytoplasm and by the biochemical analysis of FAs in shoot lipids before and after anaerobic incubation of the shoots. The experiments were carried out with intact coleoptiles after 5 and 8 days of anaerobic germination of seeds (primary anoxia) and with detached shoots, preliminarily grown in air and then subjected to anoxia in the presence of 2% glucose for 48 h (secondary anoxia). In these experiments, lipid bodies did not accumulate in the cytoplasm under anoxic conditions. Lipid bodies appeared only during 48-h anaerobic incubation of detached coleoptiles in the absence of exogenous glucose, when mitochondria degraded. There was no change either in the double bond index of FAs, or in the qualitative and quantitative composition of FAs during shoot anaerobic incubation. We conclude that neither lipids synthesized under anaerobic conditions nor esterified unsaturated FAs are involved in plant adaptation to anaerobiosis as terminal acceptors of electrons, alternative to molecular oxygen. Lipid biosynthesis under anoxic conditions, which was demonstrated for anoxia-tolerant seedlings of Oryza sativa and Echinochloa phyllopogon in experiments with radioactive precursors, ¹⁴C-acetate and ³H-glycerol, is only the manifestation of a turnover of saturated FAs and various classes of lipids, which stabilizes cell membranes under adverse conditions of strict anoxia.__________Translated from Fiziologiya Rastenii, Vol. 52, No. 4, 2005, pp. 540–548.Original Russian Text Copyright © 2005 by Generosova, Vartapetian.     

Oxygen and carbon dioxide transport by the haemocyanin of an amphibious crab,Holthuisana transversa

Summary The oxygen and carbon dioxide transporting properties of the haemolymph from an amphibious Australian crab,Holthuisana transversa were investigated. Within the temperature range 15 to 35°C increasing temperature markedly decreased oxygen affinity (H=–54 kJ·mol^–1). The Bohr effect was small at all temperatures with a mean value of –0.13. Over the temperature range 15–35°C there was a significant increase in the cooperativity of oxygen binding. Changing the concentration of Ca,l-lactate or haemocyanin in the haemolymph could elicit no significant change in either O₂ affinity or cooperativity of O₂ binding. There was no evidence in support of a specific effect of CO₂ on oxygen affinity of either non-dialysed or dialysed haemolymph.The amount of CO₂ that could be carried byH. transversa haemolymph was significantly reduced by increased temperature (approx. 14 to 12.5 mmol·l^–1 CO₂). Comparisons of oxygenated and deoxygenated haemolymph at a fixed pH were unable to demonstrate the presence of a significant Haldane effect. Combining data from oxygenated and deoxygenated haemolymph the buffer value was calculated to be in the range –6.2 to –8.5 mmol·l^–1 HCO ₃ ^– ·pH unit^–1.The insensitivity ofH. transversa haemocyanin function to all modulating influences except temperature is discussed with respect to the ecology of this crab.     

Effects of coexistence on habitat use and trophic ecology of interacting native and invasive amphipods

1. Invasive species in aquatic systems are major drivers of changes in biodiversity. Amphipods are key species in freshwaters, with invasive amphipods either replacing or coexisting with native species and often damaging local biodiversity. However, the consequences of interactions among native and invasive amphipods for their habitat use and feeding ecology and ecosystem function are not yet well understood. 2. We examined a number of streams in Brittany and Northern Ireland, with native and invasive amphipods, to evaluate the consequences of species interactions for both habitat use and diet. Our field studies centred on testing two proposed models: a cohabitation model without competition between two native species (Gammarus pulex vs Echinogammarus berilloni), and a competition model between an invasive and a native species (Gammarus pulex vs Gammarus duebeni celticus). For these three species, alone and in combination, we assessed their habitat use and feeding patterns, the latter through gut contents and stable C and N isotope analyses of their tissues. 3. When existing as single‐species populations, all three species used stream habitats broadly similarly, although G. pulex was more strongly associated with leaf litter and vegetation compared to pebble substrata than the other species. When G. pulex coexisted with either E. berilloni or G. d. celticus, the latter two changed to using all habitats equally, whereas the former retained its habitat preferences. 4. Similarly, all three species when alone had similar gut contents, with inorganic material predominating, followed by leaf and woody material and more rarely algae and invertebrates. When G. pulex coexisted with E. berilloni, the diet of the latter did not change; however, the frequency of inorganic matter, leaves and wood declined in the gut contents of G. pulex. When G. pulex coexisted with G. d. celticus, the pattern of gut contents did not change in either species. 5. When existing as single‐species populations, G. pulex had a broader range of isotopic signatures, both for δ¹³C and for δ¹⁵N, than the two other species, indicating a more variable diet among individuals. When G. pulex coexisted with either E. berilloni or G. d. celticus, the latter two had similar ranges of δ¹³C and δ¹⁵N, whereas for G. pulex the range was much less for δ¹³C and δ¹⁵N, suggesting a less diverse diet. 6. Our results infer two different modes of coexistence between native and non‐native amphipods. We have shown that the native species, which coexist stably, appear to show interference competition, leading to spatial habitat segregation, whereas competition for food and possible intraguild predation by G. pulex on G. d. celticus would explain why the distribution and density of the latter is affected by G. pulex. However, since all the species have a similar diet and feeding habit, we expect no great overall effect on ecosystem processes as a consequence of species interactions and displacements.     

The effects of hypoxia and temperature on metabolic aspects of embryonic development in the annual killifish Austrofundulus limnaeus

Embryos of Austrofundulus limnaeus are exceptional in their ability to tolerate prolonged bouts of complete anoxia. Hypoxia and anoxia are a normal part of their developmental environment. Here, we exposed embryos to a range of PO₂ levels at two different temperatures (25 and 30 °C) to study the combined effects of reduced oxygen and increased temperature on developmental rate, heart rate, and metabolic enzyme capacity. Hypoxia decreased overall developmental rate and caused a stage-specific decline in heart rate. However, the rate of early development prior to the onset of organogenesis is insensitive to PO₂. Increased incubation temperature caused an increase in the developmental rate at high PO₂s, but hindered developmental progression under severe hypoxia. Embryonic DNA content in pre-hatching embryos was positively correlated with PO₂. Citrate synthase, lactate dehydrogenase, and phosphoenolpyruvate carboxykinase capacity were all reduced in embryos developing under hypoxic conditions. Embryos of A. limnaeus are able to develop normally across a wide range of PO₂s and contrary to most other vertebrates severe hypoxia is not a teratogen. Embryos of A. limnaeus do not respond to hypoxia through an increase in the capacity for enzymatic activity of the metabolic enzymes lactate dehydrogenase, citrate synthase, or phosphoenolpyruvate carboxykinase. Instead they appear to adjust whole-embryo metabolic capacity to match oxygen availability. However, decreased DNA content in hypoxia-reared embryos suggests that cellular enzymatic capacity may remain unchanged in response to hypoxia, and the reduced capacity may rather indicate reduced cell number in hypoxic embryos.