Ontogeny of osmoregulation in embryos of intertidal crabs (Hemigrapsus sexdentatus and H. crenulatus, Grapsidae, Brachyura): putative involvement of the embryonic dorsal organ.

This study examined whether the existence of hyperosmotic internal fluids in embryos of euryhaline crabs (Hemigrapsus sexdentatus and H. crenulatus) in dilute seawater reflects osmotic isolation due to impermeability of the egg envelope, as proposed for other decapods, or active osmoregulation. When ovigerous crabs with eggs at gastrula stage were transferred from 100% seawater (osmolality 1000 mmol kg(-1)) to 50% seawater, embryogenesis and hatching of zoea were completed normally, but were delayed. Hatching failed if the transfer to 50% seawater occurred before gastrulation, and embryogenesis was abnormal in 25% seawater. In 100% seawater, embryos at all stages were internally hyperosmotic by 150-250 mmol kg(-1). On transfer to 50% seawater, osmolality initially decreased but remained 200-350 mmol kg(-1) hyperosmotic to the medium for several weeks until hatching. High efflux rates of tritium-labelled water (t((1/2)) 16-75 min) and (22)Na (t(1/2) 109-374 min) from H. crenulatus embryos were inconsistent with the osmotic isolation hypothesis. It is concluded that post-gastrula embryos were actively hyper-osmoregulating. The diffusional water permeability of the embryos decreased during development while the sodium efflux rate increased 10-fold. Very rapidly exchanging pools of water and sodium (t(1/2) a few seconds to minutes) probably corresponded to peri-embryonic fluid and implied that the egg envelope was a negligible barrier to diffusion of water and salts. Higher Na(+)/K(+)-ATPase activities in late embryos of H. crenulatus incubated in 50% seawater than in embryos incubated in full strength seawater were consistent with an acclimation response. An area of the embryonic surface located over the yolk in the region of the embryonic dorsal organ stained with AgNO(3). Staining appeared at gastrulation, persisted throughout development and was lost at hatching. Deposits of AgCl between the outer and inner membranes, identified by X-ray microanalysis, suggest that the dorsal organ was a site of chloride extrusion. A model for osmoregulation in post-gastrula embryos is proposed: osmotic uptake of water is balanced by excretion of water and salts via the dorsal organ and salt loss is balanced by active uptake over the general embryonic ectoderm.

The role of body surfaces and ventilation in gas exchange of the abalone, Haliotis iris.

The archaeogastropod Haliotis iris possesses paired bipectinate gills and normally four to six shell holes. In still water, endogenous water flow entered the branchial chamber anteriorly to the left of the head and was exhaled primarily from the three most posterior holes. The first or second anterior aperture was occasionally weakly inhalant. Cardiac interaction superimposed an oscillatory component upon ciliary ventilation but did not augment mean flow. At normal endogenous flow rates 49% of oxygen was extracted from the branchial flow, increasing to 71% at lower flows. In still water, normoxic M(O(2)) was 0.47 micromol g(-1) h(-1). Oxyregulation occurred down to P(O(2)) approximately 80 Torr, with partial oxyregulation down to 45 Torr (P (crit)), and oxyconformity below this. The oxyregulatory plateau was absent in artificially ventilated animals but normoxic M(O(2)) was higher (0.65 micromol g(-1) h(-1)). Endogenous ventilation was unaffected by hypoxia to 15 Torr. Heart rate decreased by approximately 20% at 26 Torr before falling more steeply. Oxygen uptake from the branchial ventilation stream fully accounted for normoxic M(O(2)). In hypoxia (<30 Torr), no uptake occurred from the head or foot despite extensive eversion of the epipodium. Blood oxygen measurements excluded the right mantle as a significant gas exchange organ. Changes in oxygen uptake caused by changes in the velocity of external water currents support the concept of induced ventilation and suggest that in still water aerobic respiration was ventilation-limited. Although ciliary ventilation appears adequate to support resting aerobic metabolism, induced ventilation may provide increased aerobic scope for activity and repayment of oxygen debt.

Ontogeny of salinity tolerance and hyper-osmoregulation by embryos of the intertidal crabs Hemigrapsus edwardsii and Hemigrapsus crenulatus (Decapoda, Grapsidae): survival of acute hyposaline exposure.

The adults of Hemigrapsus edwardsii and Hemigrapsus crenulatus are euryhaline crabs and strong hyper-osmoregulators. Their embryos are carried externally attached to the abdominal pleopods of female crabs, where they are exposed to temporal and spatial changes in salinity associated with their intertidal and estuarine habitats. Although embryos lack the branchial and excretory organs responsible for adult osmoregulation, post-gastrula embryos were highly tolerant of exposure to hypo-osmotic sea water. Detached eggs (embryos+envelopes), of both species, at all developmental stages between gastrulation and hatching, exhibited 80-100% survival for periods up to 96 h in sea water (osmolality, 1050 mmol kg(-1)) and in dilutions to 50%, 10%, and 1%. Cleavage stages were less tolerant of dilution; H. edwardsii, <50% survived 24 h in 10% sea water; H. crenulatus <50% survived 6 h in 10% sea water. Post-gastrulation stages strongly hyper-osmoregulated but cleavage stages were hyper-osmoconformers (maintaining internal osmolality approximately 150 mmol kg(-1) above external). Osmoregulatory capacity was reduced just prior hatching, particularly in H. crenulatus, although salinity tolerance remained high. Gastrulation therefore marks a critical stage in the ontogeny of osmoregulation and salinity tolerance. Total Na+/K(+)-ATPase activity increased greatly during embryogenesis of H. crenulatus (undetectable in blastulae; gastrulae 0.31+/-0.05 pmol P(i) embryo(-1) min(-1); pre-hatching 16.4+/-1.0 pmol P(i) embryo(-1) min(-1)). Na+/K(+)-ATPase activity increased in embryos exposed to dilute sea water for 24 h implicating regulation of this transporter in a short-term acclimation response.

Haemolymph glucose concentrations of juvenile rock lobsters, Jasus edwardsii, feeding on different carbohydrate diets.

Postprandial changes in haemolymph glucose concentration ([Glc]H) were measured in 4-day-fasted juvenile intermoult spiny lobsters, Jasus edwardsii, provided with meals composed of glycogen, maltose, sucrose, glucose, or fructose in a gelatine base, or with gels of the algal glycans agar, alginate and carrageenan. Baseline [Glc]H was 0.61+/-0.02 mmol L(-1). After consumption of glycogen, maltose or sucrose, [Glc]H approximately doubled, peaked after 3 h and returned to baseline between 12 and 24 h. Glucose and fructose meals were followed by periods of sustained hyperglycaemia lasting more than 24 h (peaking at approximately 2.5 times baseline at 6 and 3 h respectively). Suggested explanations for augmented hyperglycaemic responses to glucose and fructose are: 1) these monosaccharides by-passed contact digestion and absorption in the R-cells of the digestive gland, directing them away from storage and toward transepithelial scavenging routes; or 2) glucose and fructose directly elicited release of crustacean hyperglycaemic hormone via a chemosensory reflex. Agar and alginate induced significant postprandial glycaemic responses, consistent with reports of carbohydrases in this species and indicating their potential for inclusion in artificial diets as both binders and energy sources. Carrageenan, a highly sulphated galactan, did not produce a glycaemic response. The measurement of glycaemic responses is a quick method of obtaining nutritional information on carbohydrates considered for inclusion in formulated diets prior to lengthy growth trials.

The control of vascular resistance in the southern rock lobster, Jasus edwardsii (Decapoda: Palinuridae).

In Jasus edwardsii (Hutton) the vascular resistance of each of the seven major arterial systems leaving the heart was increased in response to several of the following neurotransmitters and neurohormones: acetylcholine, adrenalin, serotonin, dopamine, octopamine and peptides proctolin and FLRFamide-related peptide F(1). The resistance to flow through the infrabranchial sinus (IBS), part of the venous system, was also sensitive to these drugs. Unexpectedly, the responses of the IBS continued after removal of the gills. Differences in the profiles of responses of the arteries to individual hormones and in the magnitudes and the time courses of back pressure changes, eliminate a common downstream location such as the venous sinuses or gills, as the source of the arterial responses. Vasoactive drugs were effective when applied either via the lumen or, with longer delay, to the basal side of an artery via the IBS. It is concluded that the resistance of each of these sections of the vascular system is independently controllable by hormones.

Osmoregulation in the terrestrial Christmas Island red crab Gecarcoidea natalis (Brachyura: Gecarcinidae): modulation of branchial chloride uptake from the urine.

Crabs generally produce urine iso-osmotic to their haemolymph, but terrestrial crabs are able to vary the composition of their final excretory fluid (termed P) postrenally, in the branchial chambers. Regulatory aspects of branchial urine processing were investigated in the Christmas Island red crab Gecarcoidea natalis acclimated to drinking either freshwater (FW crabs) or 70% seawater (SW crabs). FW crabs released dilute P (mean [Cl(-)] 8.8 mmol l(-1)). Drinking 70% seawater caused the mean [Cl(-)] of the P to rise to 376 mmol l(-1) over 5 days, approaching the haemolymph [Cl(-)]. FW crabs with saline-perfused branchial chambers absorbed chloride at a high rate (10 mmol kg(-1) h(-1)), and haemolymph [Cl(-)] increased at approximately 20 mmol l(-1) h(-1). SW crabs exhibited elevated haemolymph osmolalities and ion concentrations and zero branchial chloride uptake. FW crabs that were salt-loaded by branchial chamber perfusion over several hours downregulated, and eventually ceased, chloride uptake. The rate of downregulation, but not the initial chloride flux, was dependent on initial haemolymph [Cl(-)]. Intravascular infusion of NaCl caused immediate reduction in branchial [Cl(-)] of 80%. Crabs ingested and regurgitated the perfusion saline, supporting suggestions that reingestion of urine could conserve water and ions. Dopamine upregulated branchial chloride transport in G. natalis. This is consistent with the ion-regulatory effects of dopamine in euryhaline marine brachyurans but contrasts with its inhibitory effects in the terrestrial anomuran Birgus latro. Dopamine increased the rate of urine release in FW crabs. Urine composition appears to be unimportant in ionic regulation, except in the case of magnesium, levels of which were elevated in the urine of SW crabs.

Oxygen uptake by embryos and ovigerous females of two intertidal crabs, Heterozius rotundifrons (Belliidae) and Cyclograpsus lavauxi (Grapsidae): scaling and the metabolic costs of reproduction.

Heterozius rotundifrons and Cyclograpsus lavauxi are crabs of similar size, whose intertidal habitats overlap. They differ in the number and size of their eggs. A 2 g ovigerous H. rotundifrons incubates 675 large yolky eggs (mean single-egg mass 269 microg; egg clutch 9.15 % of mass of female crab; increasing to 435 microg and 13.4 % at hatching). The egg clutch of a 2 g C. lavauxi is larger (15.4 % of crab mass increasing to 18.9 % at hatching) and contains more numerous (28 000), smaller (10.9 microg increasing to 20.3 microg) eggs. The longer development time of the larger eggs (194 days versus 56 days at 15 degrees C) results from a delayed increase in metabolic rate (diapause) and not metabolic scaling. On the basis of the total mass of single eggs, the mass-specific metabolic rates of early embryonic stages of H. rotundifrons (0.72 micromol g(-1 )h(-1) for the blastula stage at 15 degrees C) and C. lavauxi (1.13 micromol g(-1 )h(-1)) were similar to those of the adult female crabs (0.70 micromol g(-1 )h(-1) for H. rotundifrons and 0.91 micromol g(-1 )h(-1) for C. lavauxi) and increased 13- and 10-fold, respectively, by the time of hatching. Thus, early embryonic metabolic rates were much lower than expected from their mass, but the metabolic rates of pre-hatching embryos were consistent with the allometry of juveniles and adults. Possible interpretations of this apparently anomalous scaling of embryonic metabolic rates are discussed. Mass-specific rates of oxygen consumption by ovigerous females (including the eggs) of both species were higher than for non-ovigerous crabs, in water and in air, and increased greatly during the development of the eggs. This difference was attributable mainly to the increasing metabolic rates of the attached embryos, but early ovigerous crabs (blastula stage) of both species also demonstrated a small elevation in metabolic rate by the crab itself, i.e. a metabolic cost of egg-bearing. In contrast, the elevation of the rate of oxygen consumption by late ovigerous females of C. lavauxi was less than predicted from the metabolic rate of eggs in a stirred respirometer. This suggests that, towards the end of development in C. lavauxi, the oxygen supply to the eggs in situ may be diffusion-limited by unstirred layers, an effect not observed for the larger eggs and more open egg clutch of H. rotundifrons. The cost of development, in terms of total oxygen consumption of single eggs, from extrusion to hatching, was 3.34 micromol O2 (approximately 1.5 J) for H. rotundifrons and 0.105 micromol O2 (approximately 0.05 J) for C. lavauxi. This 30-fold ratio approximates the ratios of their initial masses and yolk contents but represents only approximately one-third of the initial energy contents of the eggs.

Physical properties and testing methods for PTFE cardiovascular patches.

Patching after endarterectomy, especially carotid artery surgery, is a common procedure to repair and close the surgical site. Both synthetic and natural materials can be used, but saphenous vein is preferred due to its greater long-term patency. In situations where it is not possible to use the saphenous vein, both Dacron and expanded polytetrafluoroethylene (ePTFE) patches have been used successfully. Expanded PTFE patches are readily available, soft and pliable, have excellent biocompatibility and do not require preclotting prior to implantation. Comparison of two types of ePTFE patches versus natural vessel show that they have more than adequate properties for their intended use.

Blood oxygen transport in the free-swimming hagfish, Eptatretus cirrhatus.

Arterial and mixed venous blood were sampled through chronically implanted cannulae from rested and swimming hagfish. PaO2 remained high when hagfish were swum for 15 min at a velocity of 20 cm s-1. PvO2 fell from 17.2 mmHg at rest to 3.5 mmHg after swimming, and the arteriovenous pH difference increased from 0.15 to 0.25 pH units. Whole blood oxygen equilibrium curves were essentially hyperbolic (Hill's n value = 1.38) and gave a half-saturation PO2 (P50) value of 12.3 mmHg at pH 7.8 and 16 degrees C. A CO2-Bohr factor (phi = delta logP50/delta pH) of -0.43 and a limited buffering capacity of the blood, amounting to approx. 4 slykes, were observed. The role of the blood in transporting oxygen and carbon dioxide both at rest and after swimming is established by in vivo blood gas measurements and in vitro oxygen-binding data. The low internal PvO2 at rest is close to the P50 measured under similar conditions and the hyperbolic equilibrium curve permits further oxygen unloading when PvO2 falls during swimming.