Hemolymph Flow Research Articles

Roles of aorta, ostia and tracheae in heartbeat and respiratory gas exchange in pupae of Troides rhadamantus Staudinger 1888 and Ornithoptera priamus L. 1758 (Lepidoptera, Papilionidae)

In non-diapausing pupae of the two birdwing butterfly species Troides rhadamantus and Ornithoptera priamus (Lepidoptera, Papilionidae) heart activity and CO 2 release rates were measured simultaneously within the initial half of pupal development. Heartbeat patterns in these pupae consist of three different types of activity: Continuous forward-pulse periods of different duration with a frequency range of about 0.25–0.52 s −1, continuous backward-pulse periods with lower frequencies (0.15–0.29 s −1) and intermittent backward-pulse periods when short series of three to 10 single heartbeats at frequencies of 0.12–0.35 s −1 alternated with heart pauses of 2–10 min. CO 2 release was discontinuous (CFO-type) from about four to 12 days after pupation in Troides rhadamantus and from about four to 18 days in Ornithoptera priamus. Mean CO 2 release rates were very low in both species (10–30 nmol g −1 min −1). After this period, heart pauses occurred more frequently, probably indicating the onset of metamorphosis and the beginning partial histolysis of the heart. Infrared-optical and thermometrical measurements of heartbeat indicated that haemolymph transport within the dorsal vessel in forward direction is more effective than in backward direction. This is deduced from the higher heartbeat frequency and heartbeat amplitude of the forward pulsations. Results from ultrasonic doppler velocimetry suggest that haemolymph flow velocity is highest during the relatively long diastasis of 2–3 s (30–40 mm s −1), while minimum particle speed (about 20 mm s −1) is at the end of systole and the beginning of diastole. This would mean that haemolymph velocity is highest between two consecutive peristaltic waves. In contrast to the haemolymph velocity, the speed of the peristaltic wave measured with the infrared transmission technique was lower (about 8.4–22 mm s −1 in Troides, 10–23 mm s −1 in Ornithoptera) and remained constant during forward pulse periods. During backward beating the speed was lower (8–20 mm s −1 in Troides, 9–17 mm s −1 in Ornithoptera) and decreased during backward pulse periods. During day two to seven in Troides and day three to nine in Ornithoptera, spiracular opening periods coincided with changes in heartbeat direction from backward to forward pulsations. A possible influence is the more efficient convective haemolymph mixing in the haemocoel during forward heartbeat. The mixing allows to bring the haemolymph in close contact with the tracheal system where the discharge of CO 2 takes place. Heartbeat may therefore serve for shortening the diffusion pathways for a rapid transition into the tracheal system during the open period of the spiracles.

Accessory hemolymph pump in the mesothoracic legs of locusts, (Schistocerca gregaria forskal) (Orthoptera, Acrididae)

An accessory pulsatile organ located in the mesothoracic legs pumps hemolymph towards the tip of the leg ventrally and towards the body near the dorsal side. It consists of a muscle attached to the ventral side of the trochanter and to the central region of a transverse connective tissue diaphragm located at the trochanter-femur border. The diaphragm has a ventral outlet that permits efferent hemolymph flow through a narrow femoral sinus. A second dorsal outlet allows the afferent countercurrent back to the thorax through a separate hemolymph channel. During abdominal ventilation, the pumping rhythm of the leg fn2 fn2 heart muscle fibers, mn, main nerve of the leg, m104, leg–heart muscle, tr, trachea, N5, main leg nerve, 5B2a, terminal nerve to the leg–heart, m107b, tibial flexor muscle. heart is neurally synchronized with abdominal ventilation. Expiratory pressure expands tracheal air sacs in the ventral trochanter and helps driving hemolymph out of this space. In idle periods of resting ventilation, an autonomous myogenic rhythm of the leg–heart can maintain hemolymph circulation in the mesothoracic leg without neural control.

Circulatory modification in the blue crab Callinectes sapidus, during exposure and acclimation to low salinity

A pulsed-Doppler flowmeter was used to measure heart rate and haemolymph flow rates in each arterial system of the blue crab, Callinectes sapidus, enabling calculation of stroke volume and cardiac output. During exposure to a 6–6–12 h salinity cycle of 100–25–100% seawater, there was an immediate increase in heart rate upon dilution of the medium. After this initial increase it decreased steadily, but remained elevated above levels in 100% seawater. A smaller increase in heart rate occurred when the salinity was raised, declining thereafter and reaching pre-treatment levels after 6 h in 100% SW. There was a slight decrease in stroke volume of the heart, but overall this resulted in an increase in cardiac output when the salinity was lowered. Differential haemolymph flow through each major arterial system also occurred. There was an increase in flow rates through the anterior aorta, anterolateral arteries and sternal artery during the first 2 h of low salinity exposure and smaller increases occurred again when the salinity was raised to 100% seawater. No significant changes in flow were observed in the hepatic arteries or posterior aorta. During a 72 h acclimation period in low salinity, similar increases in cardiac parameters and flow rates were observed in the first 6 h. These values declined to levels comparable to those in 100% seawater, after 40–50 h acclimation in low salinity. The changes in cardiovascular parameters are not directly related to the osmoregulatory physiology of this species, but appear to be due to specific behaviours occurring in response to low salinity. The results obtained here for this efficient osmoregulator are compared and contrasted with similar studies on Cancer magister, which is classified as a weak hyperosmoregulator.

The effects of progressive hypoxia on the crustacean cardiovascular system: a comparison of the freshwater crayfish, ( Procambarus clarkii ), and the lobster ( Homarus americanus )

The heart rate of crayfish (Procambarus clarkii) and lobsters (Homarus americanus) decreased (bradycardia) as partial pressure of O2 (PO2) decreased, yet cardiac output (Vb) was maintained via an increased stroke volume (Sv) to PO2s of 40 mmHg and 75 mmHg for crayfish and lobsters, respectively. Vb was redistributed in both animals. Flow through the anterior aorta increased while flow dropped through the posterior aorta and sternal artery to a PO2 of 30 mmHg; below this flow was no longer maintained in crayfish. In the lobster, flow increased to the lateral arteries and the ventral thoracic artery while flow through the anterior and posterior aortas, sternal artery and ventral abdominal artery decreased to a PO2 of 75 mmHg. Anterior hemolymph flow was maintained or increased in both animals presumably to supply nervous tissue and cephalic sense organs better. Crayfish showed an increase in intracardiac and mean arterial hemolymph pressures as PO2 declined. The increased pressures combined with the net increase in cardiac filling pressure and diastolic filling time could have accounted for the increased SV. The cardiovascular response exhibited by both the crayfish and lobster was PO2 dependent; below a critical water PO2 active compensation was no longer observed.

Activity patterns of neurosecretory cells releasing pheromonotropic neuropeptides in the moth Bombyx mori.

Short- and long-term firing patterns of neurosecretory cells releasing pheromonotropic neuropeptides in the silkworm moth Bombyx mori were examined. The cells showed three types of rhythmic changes in firing activity. Bursting activities with an interval of several seconds were synchronized with rhythmic abdominal motions for calling behavior. A slow fluctuation in firing activity over a period of several minutes depended on cyclic alternations of the flow of hemolymph. The electrical activity displayed a diel rhythm that related to light/dark cycles of the environment and sex pheromone titers in the pheromone gland. In addition to a transient inhibition of firing caused by a tactile or light stimulus, a long-term permanent inhibition was induced by mating with a fertile male. Thus, the insect neurosecretory system is highly coordinated with physiology and behavior in Bombyx mori and is influenced by external stimuli.

Endogenous rhythms of haemolymph flow and cardiac performance in the crab Cancer magister

Heart rate and arterial haemolymph flow rates were measured in freshly trapped Dungeness crabs, Cancer magister, using a pulsed-Doppler flowmeter. In the laboratory, freshly collected subtidal crabs exhibited endogenous rhythms in both cardiac function and haemolymph flow through one or more arterial systems, of both tidal and diurnal periodicity. The strongest tidal rhythms were recorded in the sternal and paired anterolateral arteries. These endogenous rhythms of selective tissue perfusion are related to an underlying locomotor activity, but may also be involved with hormonal transport or feeding. Changes in both heart rate and stroke volume were responsible for the increases in haemolymph flow rates. These rhythms were not entrained by aerial exposure, since confinement of arhythmic crabs in intertidal cages did not re-entrain an endogenous tidal rhythm. Endogenous locomotory rhythms are known to be controlled by neurohormones released in cycles from the sinus gland on the eyestalk. These hormones may also control the endogenous cardiovascular rhythms, since these were abolished after eyestalk ablation in freshly collected Cancer magister. These results suggest that hormones synthesized and released by the X-organ/sinus gland complex may, together with pericardial hormones, play a role in modulation of crustacean cardiovascular function.

Neural Control of the Lateral Abdominal Arterial Valves in the Lobster Homarus americanus.

A dorsal abdominal artery in Homarus americanus runs the length of the abdomen, giving rise to one pair of large lateral arteries in each segment. These lateral arteries supply hemolymph to the abdominal muscles and the swimmerets. In addition, many small vessels leave the dorsal abdominal artery ventrolaterally to supply the gut and gonads. Bicuspid muscular valves are located at the junction of each segmental lateral artery with the dorsal abdominal artery, but not at the origin of the gut vessels. Nerves originating from the ventral abdominal ganglia travel along the lateral arteries to innervate the valves, providing both inhibitory and excitatory inputs. Inhibitory input produces hyperpolarizing inhibitory junctional potentials that relax the valve muscles, and in intact in situ perfused arteries causes increases in outflow from the affected lateral artery. Excitatory input produces depolarizing excitatory junctional potentials that close the valves and reduce perfusate outflow. The valve nerves also branch to innervate valves up to two segments anterior and one segment posterior. Application of exogenous {gamma}-aminobutyric acid hyperpolarizes valve muscle fibers. This and the hyperpolarizing effect of valve nerve stimulation are reversibly abolished by the application of picrotoxin (10-5 M). Acetylcholine (10-5 M), but not glutamate, causes depolarization and contraction of valves. The role of the valves in controlling the distribution of hemolymph flow is discussed.

Cardiovascular functions in two macruran decapod crustaceans (Procambarus clarkii and Homarus americanus) during periods of inactivity, tail flexion and cardiorespiratory pauses

Arterial hemolymph flow was measured in restrained crayfish (Procambarus clarkii) and lobsters (Homarus americanus). Implanted pulsed Doppler flow transducers were used to measure arterial flows in the anterior aorta, posterior aorta, sternal artery, lateral artery, ventral thoracic artery and ventral abdominal artery, allowing determination of flow simultaneously in several arteries over a period of 4 days. Calculated Doppler hemolymph flow showed a strong correlation (P<0.05) with 'pumped' hemolymph flow as determined by in situ calibration. Arterial flow patterns remained constant during quiet conditions. In crayfish, cardiac output was 7.5&plusmn;1.1 ml min-1 (252 ml kg-1 min-1), of which the anterior aorta received 1.3&plusmn;0.15 ml min-1 (20.1&plusmn;4.0 %), the posterior aorta received 0.8&plusmn;0.1 ml min-1 (12.3&plusmn;2.7 %) and the sternal artery received 5.2&plusmn;1.4 ml min-1 (67.5&plusmn;37.0 %). Mean heart frequency at rest was 125.6&plusmn;5.2 beats min-1 and stroke volume was 0.06&plusmn;0.01 ml beat-1 (1.98 ml kg-1 beat-1). In lobsters, cardiac output was 60.8&plusmn;4.4 ml min-1 (93.6&plusmn;6.8 ml kg-1 min-1), with the anterior aorta receiving 7.8&plusmn;0.8 ml min-1 (12.8&plusmn;2.7 %), the lateral arteries receiving 0.6&plusmn;0.2 ml min-1 (1.0&plusmn;0.5 %), the posterior aorta receiving 12.6&plusmn;1.0 ml min-1 (20.7&plusmn;3.3 %) and the sternal artery receiving 38.9&plusmn;4.1 ml min-1 (64.0&plusmn;13.4 %). Flows in the branches of the sternal artery were 0.3&plusmn;0.05 ml min-1 (0.5&plusmn;2 %) in the ventral abdominal artery and 4.0&plusmn;0.1 ml min-1 (6.5&plusmn;0.3 %) in the ventral thoracic artery. Lobster heart rate was 82.5&plusmn;2.9 beats min-1 and stroke volume was 0.7&plusmn;0.05 ml beat-1. Periods of constant hemolymph flow were interrupted by tail flexions (abdominal flexion) and, in lobsters, periods of cardiac/respiratory pause. Tail movement increased flow (peak height and minimum flow values) in both crayfish and lobsters, although the general wave form of hemolymph flow and pressure did not change. In lobsters, periodic respiratory pauses were observed during which all arteries received hemolymph, despite the low heart rate.

ROLE OF LUNGS AND GILLS IN AN AFRICAN FRESH-WATER CRAB, POTAMONAUTES WARRENI (DECAPODA: POTAMOIDEA), IN GAS EXCHANGE WITH WATER, WITH AIR, AND DURING EXERCISE

ABSTRACT Respiratory gas transport and acid-base state were investigated in the crab Potamonautes warreni breathing air or water for at least 24 h to assess the role of the lungs and gills. The efferent pulmonary and arterial samples had similar O2 content and thus either the lungs received most of the hemolymph flow or the lungs and gills were of equal importance during air-breathing. The gills were more important in immersed crabs. The O2 partial pressure in arterial hemolymph decreased from 8.6 kPa in air-breathing crabs to 4.5 kPa in water-breathing crabs. Despite an increase in O2 diffusion limitation during water-breathing (Ldiff = 0.78) compared to air-breathing crabs (Ldiff = 0.57) the arterial-venous O2 content difference did not change. In immersed crabs, the CO, content of the hemolymph (6.1 mmol·L–1) was half that in air-breathing crabs, but the pH remained unchanged at pH 7.4. Potamonautes warreni showed no specific adaptations to the >1400-m altitude of its habitat other than apparently relatively improved O2 diffusion. Polamonauteswarreni performed well during exercise in air. Crabs exercised at slow speed (1.8 m·min–1) experienced smaller hemolymph acid-base perturbations (ApH = 0.18) than crabs exercised at fast speed (ApH = 0.36; 3 m·min–1). While the partial pressure of 0, in the arterial and efferent pulmonary hemolymph during 20 min of fast exercise decreased from near 9 to 6 kPa or less, the hemocyanin 0, saturation was maintained near 80% and the arterial-venous O2 difference doubled. An increase in Hc-O2 affinity in exercising animals partially offset the Bohr effect and assisted in 0, uptake at the gas-exchange surfaces. The relative importance of lungs and gills in gas exchange after exercise in air was apparently similar to that in resting crabs. There was little requirement for anaerobiosis during submaximal exercise. Hemolymph L-lactate levels peaked at 3.6 mmol·L–1 after 20 min of fast exercise and were similar to L-lactate levels in the muscle.

Cardiovascular Responses Resulting from Variation in External Salinity in the Dungeness Crab, Cancer magister

Haemolymph flow was assessed simultaneously in the five arterial systems leaving the heart of the crab Cancer magister, allowing calculation of stroke volume and cardiac output via heart rate. Scaphognathite beat frequency was determined via pressure measurements from within the branchial cavity. During acute exposure (6 h) to 50% dilution of normal seawater, heart rate increased, but a concurrent decrease in mean stroke volume resulted in an overall decrease in cardiac output. Initial heart rates were regained after several hours, on return to 100% seawater. Haemolymph flow rates through the anterior, anterolateral, and sternal arteries decreased during low-salinity exposure. Flow rates through the hepatic arteries remained stable, whilst flow in the posterior aorta increased. Haemolymph flow rates in all but the anterolateral arteries returned to pretreatment levels when the salinity was raised. Changes in the scaphognathite beat frequency were similar in direction to those of heart rate. In a second series of experiments, animals were acclimated to 50% seawater for 4 d and then returned to 100% seawater. After 4 d in 50% seawater, heart rates were still strongly elevated. Stroke volume was depressed but to a lower extent than observed following 6 h of exposure. On return to 100% seawater, heart rate decreased but stroke volume increased, with the result that no significant change in cardiac output occurred. It is apparent from these results that change in heart rate cannot be used to predict changes in stroke volume in decapod crustaceans. Arterial flow levels were not significantly depressed following 4 d of exposure to 50% seawater and, with the exception of a transient increase of flow in the posterior aorta, did not change significantly on return to 100% seawater. As with acute exposure, changes in scaphognathite rate again paralleled changes in heart rate. The relevance of these circulatory changes is discussed in terms of maintenance of the crabs' internal environment and behavioural or physiological adaptation.

Temperature effects on heart performance and regional hemolymph flow in the crab Cancer magister

Adult male Cancer magister crabs were subjected to a stepwise temperature change. Heart rate, cardiac output, stroke volume and hemolymph flow through four arterial systems (anterior, anterolateral, sternal and posterior) were measured using pulsed Doppler probes. Heart rate showed a positive linear relationship with temperature. The majority of acrdiac output was directed through the sternal artery, with the anterolateral arteries receiving the next largest perfusion. Temperature change resulted in an increased sternal flow. Anterolateral flow increased with a temperature increase and decreased with a temperature decrease. Results suggest that anterolateral flow may be sensitive to metabolic concerns while sternal flow may be more responsive to activity. No major hemolymph flow redirection was observed with temperature variation. Cardiac output increased initially within each experiment regardless of the direction of temperature change, while stroke volume decreased with temperature increase.

Short-term emersion affects cardiac function and regional haemolymph distribution in the crab Cancer magister

Changes in cardiac function and arterial haemolymph flow associated with 6 h of emersion were investigated in the crab Cancer magister using an ultrasonic flowmeter. This species is usually found sublittorally but, owing to the large-scale horizontal water movements associated with extreme tides, C. magister may occasionally become stranded on the beach. Laboratory experiments were designed such that the emersion period was typical of those that might be experienced by this crab in its natural environment. The frequency of the heart beat began to decline sharply almost immediately after the start of the experimental emersion period. Cardiac stroke volume fell more gradually. The combined reduction in these two variables led to a maximum decrease in cardiac output of more than 70 % from the control rate. Haemolymph flow through all the arteries originating at the heart, with the exception of the anterior aorta, also declined markedly during emersion. As the water level in the experimental chamber fell below the inhalant branchial openings, a stereotypical, dramatic increase in haemolymph flow through the anterior aorta began and this continued for the duration of the emersion period. The rapid time course of the decline in heart-beat frequency and the increase in haemolymph flow through the anterior aorta suggest a neural mechanism responding to the absence of ventilatory water in the branchial chambers. These responses may be adaptations, respectively, to conserve energy by reducing the minute volume of haemolymph pumped by the heart and to protect the supply of haemolymph to cephalic elements of the central nervous system. The decline in cardiac stroke volume, which occurs more slowly over the emersion period, may be a passive result of the failure to supply sufficient O2 to meet the aerobic demands of the cardiac ganglion.

Haemolymph flow distribution, cardiac performance and ventilation during moderate walking activity in Cancer magister (Dana) (Decapoda, Crustacea)

Adult male Cancer magister (Dana) were equipped with pulsed-Doppler flowmeters and pressure transducers for simultaneous measurement of heart and ventilation frequencies, haemolymph flow through each of the major arterial systems and cardiac output and for calculation of stroke volume. Each variable was measured at rest and during two consecutive periods of moderate treadmill walking activity and recovery. During activity, haemolymph flow through the sternal and anterolateral arteries increased, while flow through the hepatic arterial system decreased. This resulted in a redistribution of haemolymph flow in which a proportion of cardiac output was shifted from the anterior, posterior and hepatic arterial systems to the sternal arterial system. The relative proportion of the cardiac output flowing through the anterolateral artery remained constant. This indicated that oxygen supply was shifted away from the digestive system to the muscles of the walking legs and the respiratory system. Cardiac output, heart rate and stroke volume all increased in response to activity. The increase in cardiac output is the result of a large increase in stroke volume and a small increase in heart rate. A doubling of ventilation rate also occurred during activity. Both the circulatory and ventilatory systems were restored to pre-activity values by 60 min of recovery.

Mechanism of beat reversal in semi-intact heart preparations of the blowfly Phormia regina (Meigen)

The blowfly pulsatile organ is a tubular vessel consisting of an abdominal heart and a thoracocephalic aorta. Its activity consists of the regular alternance of a fast phase with a slow phase at higher and lower beating frequencies, respectively. In adult Phormia blowflies the fast and slow phases are triggered by separate pacemakers at the abdominal and cephalic vessel endings, respectively. Owing to the position of the pacemakers, impulses propagate forwards along the vessel during the fast phase and backward during the slow phase. Accordingly, haemolymph flows to the head during the fast phase and to the abdomen during the slow phase. Interspike interval and conduction velocity decrease, while spike duration and risetime increase, from the beginning to the end of the fast phase, together with the emptying of the vessel compartment where it is generated. Prevention of systolic emptying of abdominal heart compartments at the beginning of the fast phase abolishes phase alternance. Possible stretch sensitivity of the Phormia myocardium accounts for this result.

The FMRFamide-Related Peptides F1 and F2 Alter Hemolymph Distribution and Cardiac Output in the Crab Cancer magister

The FMRFamide-related peptides F1 and F2, originally isolated from lobster pericardial organs, have been shown to exert cardioexcitatory effects on isolated or semi-isolated crustacean hearts. The present study sought to determine the in vivo effects of F1 and F2 on cardiac and circulatory performance of Cancer magister using a pulsed-Doppler technique. In general the effects of F1 and F2 were similar; however, F1 was more potent and its effects were of longer duration than those exerted by F2. Infusion of either F1 or F2 caused a decrease in heart rate and subsequent periods of acardia. These decreases in rate occurred concurrently with a short-term increase in stroke volume of the heart, followed by a longer-term decrease in stroke volume. Hemolymph flow rates through the anterior aorta, anterolateral arteries, sternal artery, and posterior aorta also showed the same trend, with an initial short-term increase in flow rate followed by a longer-term decrease with periods of ischemia. Hemolymph flow through the paired hepatic arteries simply decreased, but recovery to pretreatment levels was faster than in the other arterial systems. Threshold for these responses occurred at circulating concentrations between 10(-9) mol.l-1 and 10(-8) mol.l-1 for F1 and somewhat higher, between 10(-8) mol.l-1 and 10(-7) mol.l-1, for F2.

Neural mechanisms governing distribution of cardiac output in an isopod crustacean, Bathynomus doederleini: reflexes controlling the cardioarterial valves

In Bathynomus doederleini all of the cardioarterial valves located at the origin of the lateral arteries are dilated by impulses of lateral cardiac nerves. Tactile stimuli applied to sensillar setae depress impulse activities of the 1st and 5th lateral cardiac nerves. The 1st lateral cardiac nerve controls the valve of the lateral artery which runs to the walking-legs and viscera. The 5th lateral cardiac nerve controls the valve of the lateral artery which runs to the swimmeret muscles. The response indicates that tactile receptor reflexes bring about decreased haemolymph flow to the organs. Augmented swimmeret movements were always accompanied by an increased firing rate in the 5th lateral cardiac nerve. Artificial full protraction of swimmerets simultaneously induced excitation of the 5th lateral cardiac nerve and inhibition of the 1st lateral cardiac nerve. The excitation corresponds to an increase in haemolymph flow to the swimmerets, and the inhibition a decrease in haemolymph flow to walking-legs and viscera. Three kinds of mechanoproprioceptors which were activated by swimmeret movements were found. Two of the mechanoproprioceptors are located at the base of the basipodite. The other mechanoproprioceptor supplies processes to a nerve to the retractor muscles. Activation of three kinds of mechanoproprioceptors, induced by artificial swimmeret protraction, triggered lateral cardiac nerve reflex responses.

Effect of copper on the ultrastructure of the gill epithelium of Carcinus maenas (decapoda: Brachyura)

The epithelial layer of posterior gill number 8 of the common shore crab Carcinus maenas (L.) is made up of three cell types (striated, chief and pillar). Striated cells, with an extensive network of apical and basal infoldings and large numbers of mitochondria, are implicated in ionic regulation. Chief cells contain less plasma membrane infoldings than striated cells, but have a large surface area to volume ratio, implying a predominant role in respiratory gas exchange. The ultrastructural features of pillar cells resemble those of the surrounding epithelial cell type. Thus, pillar cells may play a role in ionic regulation or respiratory gas exchange; however, pillar cells contain a well developed microtubular network, suggesting they also aid structural support and the flow of haemolymph through the gill lamellae. A sublethal copper concentration (50 μg l −1) administered at 35‰ and 10‰ salinity in a flow-through system caused extensive ultrastructural alteration to the gill epithelial cells, including a decrease in the number of plasma membrane infoldings (and associated mitochondria); extensive vacuolation; a change in ribosomal distribution; and disruption of the microtubular network. The extent of the changes was greater at 35‰ than at 10‰ salinity. This paper describes these gill effects in detail, and correlates the ultrastructural changes to previously documented physiological responses of crustaceans exposed to sublethal copper concentrations.

FINE STRUCTURE OF THE GILLS OF THE FRESH-WATER SHRIMP MACROBRACHIUM OLFERSII (DECAPODA): EFFECT OF ACCLIMATION TO HIGH SALINITY MEDIUM AND EVIDENCE FOR INVOLVEMENT OF THE LAMELLAR SEPTUM IN ION UPTAKE

ABSTRACT The microanatomy and ultrastructure of the sixth gill of the fresh-water shrimp Macrobrachium olfersii was examined in shrimps maintained either in fresh water or acclimated to a high salinity medium (HSM, sea water of 21‰) for 10 days. At its base in the gill shaft, each phyllobranchiate lamella possesses a central afferent vessel and 2 lateral efferent vessels. The lamella exhibits a nonfenestrated, medial septum over its full extension which divides the lamella into 2 compartments through which hemolymph flow is directed by pillar cells disposed perpendicularly above and below the septum. The pillar cells possess apical microvilli apposed to the cuticle, while their basal regions are strongly attached to the septal cells by areas of desmosomal contact. Wide apical flanges spread radially from the columnar pillar cells as sheets of thin cytoplasm of about 850 nm in thickness. The flanges also exhibit microvilli, and adjacent flanges are connected by areas of septate junctions; there is no elaboration of the basolateral membrane. The pillar cells and their flanges are overlaid by a thin cuticle (175 nm thick), resulting in a hemolymph-water diffusion barrier of about 1 μm in the region of the flanges. The septal cells are rich in mitochondria and exhibit numerous infoldings of their plasma membrane which individually envelop each mitochondrion, probably providing an energy source for active salt transport through the pillar cells. The gill can thus be considered a mixed function gill with a dual role in gas exchange and salt transport. The 10-day acclimation period to HSM induced changes in this basic arrangement, quantified by morphometric analysis. The surface density of the plasma membrane infoldings increased significantly from 2.01 ± 0.15 μm2 membrane/μm3 cytoplasm in shrimps maintained in fresh water to 2.91 ± 0.19 μm2 membrane/μm3 cytoplasm in those acclimated to HSM. The infoldings themselves became arranged in stacked layers separating the mitochondria (7.07 ± 1.51 cf. 13.73 ± 2.48 test segments intersecting more than one invagination). The mitochondrial volume fraction (12.56 ± 0.69 cf. 14.26 ± 0.71%) was unchanged as was the length to width ratio of the mitochondrial profiles (2.74 ± 0.17 cf. 3.23 ± 0.18). The data are discussed in terms of the significance of the physical coupling between membrane invaginations and mitochondria in the septal cells, and in terms of the possible evolution of the lamellar structure in the phyllobranchiate gills of the Palaemonidae.

VENTILATORY AND VASCULAR ROUTES IN A SAND-BURYING SWIMMING CRAB, OVALIPES CATHARUS (WHITE, 1843) (BRACHYURA: PORTUNIDAE)

A B S T R A C T Ovalipes catharus is a burrowing portunid which utilizes both forward and reverse ventilation. The proportions of time spent in each ventilatory mode depend upon burial state and activity. In forward ventilation, water enters the hypobranchial space of the branchial chambers at the bases of the legs, flows between the gill lamellae to the epibranchial space, and is exhaled anteriorly via the prebranchial apertures lateral to the mouthparts. This flow is countercurrent to the general hemolymph flow in the gills. In reverse-ventilating crabs, water enters anteriorly into the epibranchial space. Most of this water does not ventilate the lamellae, but passes between the epibranchial surfaces of the gills and the branchiostegites to be exhaled posteriorly between the fourth and fifth pereiopods. A variable (usually minor) fraction of the water exits from the Milne Edwards apertures, presumably taking a concurrent, epibranchial to hypobranchial, route. The arterial and venous circulations are described from vascular casts. From these the potential for the branchiostegal circulation to function as an alternative site for respiratory gas exchange was examined. Each branchiostegite is extensively vascularized with a sheet of interconnecting sinuses and lacunae. Hemolymph enters anteriorly from the hepatic sinuses and is returned to the pericardium laterally and posteriorly, thus forming a vascular shunt parallel to the branchial circulation. It is unclear whether the branchiostegite is important in gas exchange in this crab. Vascular casts of a number of other significant structures, including the heart, cor frontale, and antennal glands are described.

Patterns of haemolymph-flow variation in decapod crustaceans

Adult male Dungeness crab, Cancer magister, were trapped in the Barkley Sound region of Vancouver Island, British Columbia during June 1992 to August 1993. Heart rate and haemolymph flow through the five major arterial systems were recorded in resting undisturbed C. magister using a pulsed Doppler flowmeter. This technique allowed calculation of the stroke volume of the heart as well as cardiac output. The heart rate of 62 C. magister conformed to a normal distribution, whereas haemolymph flow through individual arteries was exponentially distributed. Stable haemolymph flow through all arterial systems was observed in only about 5% of the individuals tested; more often, haemolymph flow in one or more arteries fluctuated independently of flow through the remaining arteries. Several typical patterns of variation in cardiovascular parameters are described and related to possible underlying control mechanisms.