Haemolymph Osmotic Pressure Research Articles

The effect of osmotic hysteresis on volume regulation in Mytilus edulis

1. 1. When Mytilus edulis was transferred from 600 to 300 mOsm, the hemolymph osmotic pressure decreased with a rate constant of 0.077 ± 0.0097. Irrigation of the mantle cavity increased the rate constant to 0.50 ± 0.05. 2. 2. When mussels were transferred from 300 to 600 mOsm, the hemolymph osmotic pressure increased with a rate constant of 0.721 ± 0.095. Inhibition of lateral cilia with dopamine decreased the rate constant to 0.615 ± 0.0509. 3. 3. During hypoosmotic stress, irrigation of the mantle cavity increased the magnitude of water gain, sped recovery in whole animals but slowed recovery in isolated tissue. 4. 4. During hyperosmotic stress, addition of dopamine decreased the magnitude of water loss and sped recovery in whole animals, and isolated tissue.

Water-regulatory behaviour in terrestrial gastropods.

Summary1. Terrestrial snails and slugs are exceedingly susceptible to dehydration due to evaporative water loss from the integument and lung surface, and the deposition of a dilute mucous trail. Active slugs can lose 30–40% of their initial body weight (IBW) within 2 h.2. Both field and laboratory studies have revealed that habitat selection by snails and slugs is well correlated with the availability of water. In addition, numerous species display homing behaviour, returning directly to their moist secluded daytime resting sites at dawn.3. Several aspects of locomotor activity are affected by body hydration and environmental conditions such as relative humidity. Moist conditions result in termination of aestivation in snails and a generally higher level of activity in both snails and slugs. In contrast, severe dehydration initiates aestivation in snails and an increase in the intensity and duration of circadian locomotor activity in slugs.4. Huddling behaviour is a specialized example of the general preference of slugs for moist habitats. When groups of slugs are exposed to dry environmental conditions, they form closely packed aggregations. This response results in a decrease in the rate of dehydration of the individual slugs.5. When slugs have been dehydrated to about 90% IBW, rhythmic closures of the pneumostome are initiated. As dehydration progresses there is a reduction in the open diameter of the pneumostome. These responses reduce the total exposure of the lung surface and thereby evaporative water loss. In slugs dehydrated to about 80 % IBW, these responses can result in a 7 % reduction in water loss. 6. When slugs have been dehydrated to about 65% IBW (67·6 ± 4·3% IBW) they move on to a moist surface, assume a characteristic flattened posture and remain quiescent while water is absorbed through the surface of the foot. Once they are rehydrated (to 93·5 ± 12·4% IBW) they move off the moist surface. Thus there exists a specific dehydration threshold for the initiation of contact‐rehydration and a rehydration set‐point at which the response is terminated.7. Both initiation and termination of contact‐rehydration are controlled by variations in haemolymph osmotic pressure. The behaviour can be experimentally initiated by injection of hyperosmotic mannitol solution and terminated by injection of dilute saline.8. Contact‐rehydration involves bulk flow of water through an epithelial paracellular pathway in the integument of the foot. The rate of absorption of [14C]inulin during contact‐rehydration is similar to that of water. The efficacy of water movement through the pathway is modulated by body hydration, the pathway being opened only in dehydrated slugs.9. By means of the dual‐limit control of contact‐rehydration slugs can behaviourally regulate their body hydration and haemolymph osmolality within the tolerable hydration range described by the upper and lower limits.

Fluid Secretion By the Malpighian Tubules of the Dragonfly Libellula Quadrimaculata

ABSTRACT Fluid secretion by the Malpighian tubules of Libellula quadrimaculata is unusual in that it is dependent on sodium and entirely independent of potassium in the external medium. It is suggested that this is due to the primitive, sodium-rich haemolymph of the Odonata. Similarities between these tubules and those of the millipede Glomeris marginata, which has a similar sodium-based haemolymph, support this view. Fluid secretion by the tubules is also dependent on the osmotic pressure of the external medium, declining considerably at higher osmotic pressures. However, there is no difference in the secretory rates of tubules isolated from larvae adapted to tap water, de-ionized water or salt water, even though there are large differences in the haemolymph osmotic pressure under these different conditions. This suggests some form of adaptation of the tubules in larvae from these different conditions. A factor which causes a five-to six-fold increase in the rate of secretion was present in the thoracic ganglia, and a slightly lower increase in secretion rate was recorded in larvae that had been feeding.

Relative humidity affects the intercellular spaces and cell contacts of the kidney epithelium of the terrestrial snail Helix aspersa müller

The effects of relative humidity on hemolymph osmolarity and on kidney ultrastructure are explored in Helix aspersa. The snails are active at 95% relative humidity and less active at 50% relative humidity. The hemolymph osmotic pressure increases with the decrease of relative humidity. Pericardial fluid and hemolymph collected from the heart contain similar amounts of total proteins, and both fluids display hemocyanin molecules in negatively stained preparations. When the snails are kept in an atmosphere of 95% relative humidity, numerous wide intercellular spaces are observed in the single-layered-kidney epithelium. The spaces are almost absent when the snails are kept at 50% relative humidity. It is suggested that prourine is formed through a paracellular junctional pathway across the single-layered kidney epithelium, and that the pericardial cavity is not the site of prourine formation. The septate junctions joining the kidney epithelial cells form a continuous belt of intimate contact in the paracellular pathway of prourine. Long septate junctions with many septa are present in the kidneys of snails from the atmosphere of 50% relative humidity, whereas short septate junctions with fewer septa are found in the kidneys of snails from the atmosphere of 95% relative humidity. It is possible that the longer septate junctions with many septa reduce prourine formation across the kidney sac epithelium.

Hydration‐induced modulation of feeding responsiveness in terrestrial slugs

AbstractIn various species of animals the level of body hydration is known to affect feeding responsiveness. In order to understand the mechanisms that underlie this form of behavioral modulation, hydration‐induced changes in feeding have been examined in the terrestrial slugs Limax pseudoflavus and Lehmannia valentiana. Air‐dehydration of slugs to 70–60% of initial body weight (%IBW) abolishes feeding. Feeding responsiveness is rapidly restored in these slugs after they are allowed to rehydrate in contact with a moist surface. Injections of hyperosmotic mannitol or sucrose solution also result in abolition of feeding, thus suggesting that hemolymph osmotic pressure is involved in modulation of the feeding response. Correspondingly, if mannitol‐injected or air‐dehydrated slugs are injected with 0.1 × saline, feeding is restored in a manner similar to that observed following contact‐rehydration. Feeding was restored, however, only in those slugs whose hemolymph was diluted to at least 180–190 mOsm/kg H2O, which is the hemolymph osmolality of slugs at 75–70% IBW. The present results are consistent with the hypothesis that hydration modulation of feeding in slugs is mediated by hemolymph osmotic pressure.

Effect of elevated temperature on osmotic and ionic regulation in a salt-tolerant caddisfly from Death Valley, California

The effects of temperature (8–10 or 20°C) on regulation of haemolymph osmotic and ionic concentrations were investigated over a range of salinities (0–25‰) in fifth-instar larvae of the Death Valley caddisfly Limnephilus assimilis. At low temperatures, levels of chloride and sodium in the haemolymph are regulated over a wide range of salinities corresponding to the salinities at which larvae occur in nature and at which they can complete development into adults. In contrast, haemolymph osmolality is constant at low salinities (<14‰) but approaches conformity with the medium at higher salinities. High temperature reduces the larva's ability to maintain low chloride concentrations in its haemolymph and also leads to a reduction in haemolymph osmotic pressure; thus, at high temperatures ions account for more of the haemolymph osmotic concentration than at low temperatures. These data suggest that the absence of larvae from thermal pools and from all Death Valley waters in summer can be explained by the effects of high water temperatures on hydromineral regulation.

Free Amino Acids as Regulators of Osmotic Pressure in Aquatic Insect Larvae

ABSTRACT Microanalytical techniques are used to show that organic molecules play an important role is osmoregulation. Changes in the inorganic ion composition of haemolymph from fourth instar larvae of Aedes aegypti are correlated with the changes in the concentration of organic ions. Free amino acids have a significant role in regulating haemolymph osmotic pressure with respect to the osmotic pressure of the water in which the animal lives. Mechanisms by which amino acid levels could respond to changes in salt concentration are discussed.

Why don't tobacco hornworms (Manduca sexta) become dehydrated during larval‐pupal and pupal‐adult development

AbstractStudies of water loss during metamorphosis of insects have usually been confined to the pupal stage where both cuticular and respiratory control of transpiration have been reported. In Manduca sexta and other lepidopterans, preparation for pupation actually begins several days before pupation when the animals stop feeding and begin searching for an appropriate pupation site, a burrow for M. sexta. This study examines some aspects of water balance maintenance from the initial period of searching to the final time of eclosion. Behavior is important for reducing water loss, as animals which fail to find an appropriate pupation site continue to lose water at twice the rate of animals which are burrowed (10 vs. 5 mg H2O/g·h). Part of this is explained by exposure to light as unburrowed animals in constant dark are intermediate in water loss. The epicuticle during the pupal stage reduces water loss rate eight to tenfold, removal causing animals to lose water at 4 mg (g·h)−1. M. sexta does appear to be capable of storing water in preparation for metamorphosis, since individually raised animals consistently have water contents higher than animals reared in large groups. A drop in water loss during the larva‐pupal development is correlated with increased hemolymph ecdysone titer, although how is unknown. Pupal water loss can be divided into cuticular and respiratory pathways, with cuticular loss accounting for two‐thirds of 0.7 mg H2O (g·h)−1 loss rate. Finally, an increase in hemolymph osmotic pressure just prior to ecdysis may aid in reclamation of molting fluid.

Ultrastructural changes in the gut and the Malpighian tubules of Epilachna varivestis after application of the new antibiotic Nikkomycin involve an osmoregulatory defect

The effect of the antibiotic Nikkomycin was investigated on the Malpighian tubules and the gut of fourth-instar larvae of the Mexican bean beetle, Epilachna varivestis. Within the Malpighian tubules, three different stages in cell alterations can be recognized. A stage of increased activity (Stage A), and two stages of dedifferentiation (Stages B and C) which are distinguishible by characteristic mitochondrial morphology. In Stage C individuals, when Malpighian tubule function stops entirely, alterations in the midgut take place, that are signs of increased activity. Measurements of hemolymph osmotic pressure showed that there is a considerable increase to a higher level which is maintained. Compared with the ultrastructural data, the regulation of osmotic pressure on a higher level may, in part, be the result of compensation for the failure of Malpighian tubule function by the midgut.

Water balance and osmoregulation in a free-ranging tenebrionid beetle, Onymacris unguicularis, of the Namib Desert

Onymacris unguicularis, a fog-basking tenebrionid beetle of the Namib Desert, has mean water influx rates of 49.9 mg H 2O/g.d and mean efflux rates of 41.3 mg H 2O/g.d with mean mass gain being 10.7 mg/g.d. If only steady-state conditions are considered (no mass change), and passive vapour input subtracted, drinking accounts for 50% of water input. Active beetles must drink in order to maintain water balance, while inactive beetles can maintain water balance either eating seeds or by simply metabolizing fat. Little change is observed in ratios of haemolymph and total body water to dry mass when fogs occur, while significant changes in haemolymph osmotic pressure are associated with fog occurrence. For short periods, O. unguicularis can tolerate dehydration with only slight changes in the ratio of total body water and haemolymph to dry body mass and to haemolymph osmotic pressure. For longer periods however, active beetles must have access to fog water for water balance maintenance. This is probably necessary for reproduction.

Osmoregulation in Chironomus tentans (Fabr.), Chironomus riparius meigen, and Chaoborus punctipennis (say)

1. 1. Seasonal variations of hemolymph ion concentration and hemolymph osmotic pressure were examined in two species of benthic macroinvertebrates each in two lakes in central Oklahoma. 2. 2. Variations in ion concentration among stations were not significant in either lake, although two stations in Ham's Lake were destratified in summer by pumping while one station remained stratified. 3. 3. Mean month concentrations of Na + ions in the hemolymph of Chironomus tentants ranged from 73 to 120 mM. while the maximum mean for K + was 8 mM. Values for Cl − ions were about one half the levels of Na + Osmotic pressure ranged from 0.25 to 0.43—Δ° C. 4. 4. The ionic composition of the hemolymph was lower in Chironomus riparius in Ham's Lake in spring and fall than in summer. No seasonal trend was observed for C. tentans in Arbuckle Lake and the trends for Chaoborus punctipennis were opposite in Arbuckle and Ham's lakes. 5. 5. The correlation coefficients between Na + or Cl − ions in the hemolymph and osmotic pressure were all significant. 6. 6. In laboratory experiments, the hemolymph ion concentrations of C. riparius and C. punctipennis increased with temperature and salinity and decreased with dissolved oxygen concentration (DO). In a factorial design, the interactions between DO × salinity and DO × temperature were significant.

The influence of salinity on the cuticular permeability of Cenocorixa bifida hungerfordi Lansbury (Hemiptera: Corixidae)

The cuticular permeabilities of individual Cenocorixa bifida hungerfordi Lansbury collected over a wide range of salinities were determined. Corixids from low salinity water (0–2000 μmhos∙cm−1 surface conductivity at 25 °C) exhibited low cuticular permeability, whereas those from moderately saline water bodies (7000 – 11 000 μmhos∙cm−1) were much more permeable. However, at higher salinities cuticular permeability was again low; corixids from a lake with a surface conductivity of 16 000 μmhos∙cm−1 (approximately half that of seawater) had cuticular permeabilities comparable with those of corixids from freshwater lakes. This phenomenon was shown to be acclimatory, since permeability decreased over time when corixids from moderately saline lakes were placed into distilled water. The biological reasons for these results are not clear, but it appears that cuticular permeability of C. bifida increases as problems of ion regulation diminish, and then begins to decrease, seemingly at the salinity at which it becomes difficult for the corixid to maintain a constant haemolymph osmotic pressure. The biological implications of this phenomenon are discussed.

Water balance in Collembola and its relation to habitat selection: Water content, haemolymph osmotic pressure and transpiration during an instar

In the two collembolan species Orchesella cincta and Tomocerus minor the water content, haemolymph osmotic pressure and transpiration rate fluctuate with the feeding rhythm during each instar. The changes in water content, however, are due to changes in dry weight, because the absolute water weight stays constant during the instar. The intake of food is probably the cause of the increase in haemolymph osmotic pressure. Increase of osmotically active substances in the blood and/or blood volume reduction may be responsible for the rise in osmotic pressure. This change in osmotic pressure in turn may affect the responsiveness of the animals to water as well as their feeding behaviour. Changes in the epicuticle and in epidermal cell membranes may cause changes in the rate of transpiration. The high rate observed during ecdysis and during the mid-instar may explain the behaviour of the animals in varied water conditions. Dehydration during the instar causes an equivalent rise in osmotic pressure for both Tomocerus minor and Orchesella cincta. The water loss appears to involve the haemolymph. The physiological state of the animal does not influence the rise in osmotic pressure. There are no signs of any osmoregulation in the two species.

The relationship of hemolymph osmotic pressure to spermatogenesis in the tobacco budworm,Heliothis virescens

The hemolymph osmotic pressure of male Heliothis virescens last instar larvae and pupae can be correlated with the state of spermatogenesis: intermediate (approx. 325 mOsm/kg) osmotic pressures are found in pre-meiotic animals, low (approx. 300 mOsm/kg) osmotic pressures characterize meiosis and elongation, and high (approx. 370 mOsm/kg) osmotic pressures, characterize the tests of diapausing pupae, where mature sperm have disappeared and only pre-meiotic sperm are found. In vitro studies show that, as the osmotic pressure of the medium is increased, spermatogenesis is inhibited and the survival of pre-meiotic cysts is enhanced. It is proposed that the osmotic pressure of the hemolymph plays a role in spermatogenesis and in the preservation of immature cysts during diapause.

Adaptations of Nymphs of a Marine Dragonfly, Erythrodiplax berenice, to Wide Variations in Salinity

Nymphs of the dragonfly, Erythrodiplax berenice, are common on rocky mangrove flats in the lower Florida Keys at salinities of 36-48 ppt. Erythrodiplax berenice appears to be the only truly marine odonate, and the nymphs are able to tolerate wide variations in salinity. Hemolymph osmotic pressures for nymphs freshly captured in seawater or held in artificial seawater were 358-412 mOsm. There was little further variation at salinities between freshwater and 260% seawater (2,612 mOsm). In 300% seawater, hemolymph osmotic pressure rapidly increases to about 1,000 mOsm, and death ensues. The transition point between hyper- and hypoosmotic regulation occurred at approximately 350 mOsm seawater. Freshwater- and seawater-acclimated nymphs differ little in body water content (about 80%), but Na content is elevated from 50 to 89 Mmol/g wet wt, respectively. In 35 ppt seawater, Na influx and efflux were approximately balanced near 400 μmol/100g·h. In freshwater (1 mM Na), these fluxes decline to about 10 μmol/100g·h. The time for complete turnover of body Na increases from 0.9 day in seawater to 21 days in freshwater. On rapid transfer from water of 470 mM Na to water of 1 mM Na, the Na efflux in 1 mM was only slightly higher than expected for freshwater-acclimated nymphs. At a water Na level of 0.25 mM, Na efflux increases greatly, and there is a large net loss of Na. Water influxes of nymphs in distilled water or 35 ppt seawater were similar (33 and 40 μ1/g·h, respectively); complete turnover of body water occurs in about 0.8 day. Nymphs of E. berenice rival the better-known dipterans in osmoregulatory abilities and should be studied further to compare mechanisms of hypoosmotic regulation that have presumably evolved independently in these two orders.

Water balance in Collembola and its relation to habitat selection; cuticular water loss and water uptake

In the order Collembola a clear relationship was found between overall cuticular water loss and water conditions of the habitat. The different transpiration rates were negatively correlated with the haemolymph osmotic pressure, but there was no clear causal relationship. In two species, Orchesella cincta and Tomocerus minor, which live sympatric but have a different micro-distribution (partly due to small scale heterogeneity in water conditions), important differences exist both in rate of water loss and in speed of water uptake: Orchesella cincta had a significantly lower transpiration and a higher speed of water uptake than Tomocerus minor. The transpiration rates of both species were linearly related to the vapour pressure deficit of the ambient air. Contrary to Orchesella cincta, Tomocerus minor lost water in saturated conditions. Freshly-killed Orchesella cincta had a higher transpiration rate than living individuals, but in Tomocerus minor there was no such difference. It is suggested that the main integumentary resistance against water loss in Orchesella cincta is the epidermal cell and in Tomocerus minor the epicuticle. The important rôle of the ventral vesicles in the water relations of Collembola was confirmed.

Changes in osmotic pressure and sodium concentration of the haemolymph of woodlice with progressive desiccation

1. 1. Haemolymph osmotic pressure was measured in four species of woodlouse after pre-treatment in 100% R.H. followed by progressive desiccation. 2. 2. Considering sexes together it was found that Oniscus asellus cannot osmoregulate but that Porcellio scaber and Armadillidium depressum can. Ligia oceanica showed a greater osmoregulatory ability during aerial desiccation than some other “more terrestrial” species. All species except A. depressum showed considerable sexual variation in their response to desiccation even though the pre-treatment values were similar. 3. 3. Sodium levels were monitored with progressive desiccation in O. asellus and P. scaher. Contrary to expectation the former species showed greater sodium control than the latter.

Hydromineral regulation in the saline water corixid Trichocorixa reticulata (Hemiptera: Corixidae)

The aquatic corixid Trichocorixa reticulata (Guerin-Meneville) inhabits coastal marshes, brackish water ponds and salt ponds of high salinity, suggesting the presence of well developed mechanisms for hydromineral regulation. Groups of corixids acclimated in salinities ranging from fresh water to just above 300% sea water (100‰) were analyzed for total body water content, haemolymph ionic and osmotic levels, and haemolymph free amino acids. Results indicate an excellent ability to maintain haemolymph Na +, Cl −, Mg 2+ and K + hyperosmotic to the medium at low salinities and hyposmotic at high salinities. Calcium appears to conform closely to changes in external medium, becoming hyposmotic at very high salinities (80‰). Total haemolymph osmotic pressure was well regulated, the freezing point depression varying from 0.75°C in distilled water to 1.15°C in salinities of 100‰. Total body water was maintained at approx. 75% of the total animal wet weight at all salinities tested. Free amino acids were maintained between 40–60 mM in all tests and did not appear to change with salinity.

The response of Mytilus edulis to short duration hypoosmotic stress

1. 1. Valve movements monitored from Mytilus edulis acclimated to 34‰ SW during exposure to low salinity indicate that the shell is not used to isolate the mussel from hypoosmotic SW when the salinity is 17‰ or greater. 2. 2. The water content of the whole animal, gill and posterior adductor muscle tissue; hemolymph osmotic pressure, Na +, and Cl − concentrations were determined hourly for 9 hr in mussels with valves propped open and exposed to five hypoosmotic salinities from 25.5 to 3.4‰. 3. 3. Water loading was essentially complete within the first 2hr of exposure: whole animal water content increased 26.51 g H 2O/100g wet tissue in 11.2‰ while the gill tissue water content increased only 2.48 g H 2O/100g wet tissue. During the first 2hr of exposure hemolymph osmotic pressure decreased 200–250 mOsm, regardless of salinity, and at all salinities below 25.5‰ the hemolymph remained hyperosmotic to the medium for the 9 hr of the experiment. 4. 4. When taken together, these data suggest physiological mechanisms other than valve closure are responsible for tolerance of short duration hypoosmotic stress in Mytilus edulis.

Sequestration of haemolymph sodium and potassium by fat body in the water-stressed cockroach Periplaneta americana

Cockroaches that were dehydrated for 8 days lost 50% of the body water, with haemolymph volume decreasing from 18.9% to 9.3% of total wet weight. Haemolymph osmotic pressure. Na + and K + corcentrations were regulated within narrow limits (O.P. 413–459 mOs/Kg; Na + 185 – 210 mM; K + 16.0–19.5 mM). Rehydration of dehydrated insects restored the haemolymph osmalality and Na + and K + concentrations to near original levels within 24 hr. During dehydration 1219 μg Na + (expressed as NaCl) and 158 μg K + (expressed as KCl) were removed from the haemolymph. Only 4% (approximately) of these amounts were excreted. Na + and K + ingestion and excretion being virtually in balance. The Na + and K + removed from the blood was entirely accounted for by the observed increase in Na + and K + concentrations in the fat body (Na + 11.02–18.10 mg/g: K + 31.85–43.78 mg/g expressed as chlorides during dehydration. The increase in K + in the fat body at day 8 was approximately eight times the amount of K + removed from the haemolymph. It is suggested that this is due to a transfer of intracellular K + from other tissues. The rate of uptake of these cations appears to show saturation kinetics. It is suggested that K + and possibly Na + are sequestered as urates in the fat body by a reversible process.