Gastric processing in the Dungeness crab, Cancer magister, during hypoxia

The gastric physiology of the Dungeness crab, Cancer magister, was investigated over a range of oxygen tensions. Postprandial crabs reacted differently to hypoxia compared with unfed animals. The bradycardic response in postprandial animals was reduced, suggesting a summation of responses with feeding. A similar pattern was observed for ventilation rate. In unfed animals ventilation rate increased slightly as oxygen levels declined, but dropped significantly in oxygen tensions below 3.2 kPa, whereas in postprandial crabs it increased significantly in the lower oxygen regimes. Gastric processing of the meal was followed using a fluoroscope. Pyloric contraction rates were maintained during mild hypoxia, but decreased in 5.3 kPa oxygen tension and below. This led to an increase in clearance times of digesta from the foregut, midgut and hindgut regions. The slowing of gastric processing in the lower oxygen tensions suggested that the animals were unable to maintain their internal oxygen concentration. A significant reduction in efficiency of assimilation only occurred in the lowest oxygen regime tested (1.6 kPa). The range of hypoxia where gastric processing was affected corresponded closely to the levels of oxygen that modulate the foraging behaviour of C. magister. By using both physiological and behavioural mechanisms C. magister can maintain digestive processes, even in severely oxygen depleted environments.     

Responses of bender apodeme tension receptors in the Dungeness crab,Cancer magister

Receptors monitoring tension are located on the apodemes of the bender (productor propoditis) muscle of walking legs and chelipeds of the Dungeness crab, Cancer magister. The bipolar neurons form a nerve, the bender apodeme sensory nerve (BASN), which joins the CP1 chordotonal organ nerve proximally, BASN units exhibit spontaneous activity at rest, and fire bursts of action potentials to rapid passive reduction of the carpopodite-propodite joint. Isometric contraction of the bender muscle results in BASN output that is directly related to force. Afferent activity ceases upon quick release of isometric tension, when tension drops to zero, and the unloaded muscle contracts isotonically.     

Isolation and characterization of polymorphic microsatellite loci from the Dungeness crab Cancer magister

The Dungeness crab, Cancer magister, is the focus of one of the most intensely harvested fisheries in North America. Given its economic importance, there is considerable interest in assessing the degree and spatial pattern of genetic structure in C. magister. To that end, we developed a series of 17 hypervariable microsatellite loci. Six of these 17 loci could be amplified in a single multiplex PCR reaction. Using dye‐labelled primers all six loci can be coamplified and scored simultaneously on an automated sequencer. The ability to multiplex multiple loci greatly increases the ease and speed of genotyping for this species.     

Larval settlement of the nemertean egg predator Carcinonemertes errans on the Dungeness crab,Metacarcinus magister

Due to their habitat specificity, marine parasites present excellent systems for studying the processes and patterns of larval settlement. Settlement of Carcinonermertes errans, an egg predator of the Dungeness crab, is described here for the first time. Upon contact with a host individual, competent larvae of C. errans settled on the crab's exoskeleton and migrated under the abdominal flap within 24 h. When removed from the host, recently settled worms retained their larval characteristics. After 48 h on the host, however, metamorphosis proceeded and larvae became juvenile worms. Additional field studies showed that competent larvae were present in the waters of the Coos Bay Estuary during the months of August through early November, could infect crab hosts directly from the water column, and exhibited density‐dependent gregarious settlement.     

The competitive and predatory impacts of the nonindigenous crab Carcinus maenas (L.) on early benthic phase Dungeness crab Cancer magister Dana

We evaluate the potential competitive and predatory impacts of nonindigenous European green crab Carcinus maenas on native Dungeness crab Cancer magister in the northeast Pacific. The coastal estuaries of Washington State, USA, provide appropriate habitat for recently introduced green crab, yet these areas are important nursery grounds for Dungeness crab and contribute greatly to the coastal crab fishery. Juvenile Dungeness crabs are dependent on limited intertidal epibenthic shell for refuge habitat during early benthic life and experience increased mortality on open sand and mud as a result of predation by fish and birds. Early juveniles throughout the subtidal are similarly at risk due to predation by fish and especially adult conspecifics. Laboratory experiments and infrared video observations revealed that juvenile green crab displace Dungeness crab of equal size from shelters during one-on-one competition. Green crab also consistently win nocturnal foraging trials in which the species compete for fresh, damaged clams. Field and laboratory enclosure experiments show that juvenile Dungeness crab emigrate from oyster shell habitat as a result of competition and predation by adult green crab. Depending on the extent to which the two species overlap, interactions with the dominant nonindigenous species could have a negative influence on juvenile Dungeness crab survival and could conceivably impact recruitment to the fishery. However, current evidence indicates that the distribution of green crab in Washington State is far removed from nursery areas of Dungeness crab.     

Gastrin/cholecystokinin-like immunoreactive peptides in the Dungeness crab, Cancer magister (Dana): immunochemical and biological characterization

The purpose of this investigation was to characterize a gastrin/cholecystokinin-like immunoreactant (G/CCK-LI) extractable from the crab, Cancer magister. G/CCK-LI was extracted best in boiling water and was found mainly in the stomach, hemolymph and carapace. A relatively large immunoreactive peptide in the stomach and apparently smaller forms in the hemolymph and carapace were separated by Sephadex G-50 fractionation. Anion-exchange chromatography further fractionated the stomach form into three major peaks. The crab material cross-reacted with three antisera specific for the common C-terminus of gastrin/CCK, but cross-reacted much less with three antisera directed against other portions of the gastrin molecule. Partially purified crab stomach G/CCK-LI inhibited the binding of labeled CCK to mouse brain G/CCK receptors but not to rat pancreatic CCK receptors. The crab peptide did not stimulate rat gastric acid or rat pancreatic amylase secretion. These results indicate that the crab peptides are structurally similar to, but distinguishable from, the bioactive C-terminal amino acid sequence common to gastrins and CCKs.     

A mycosis caused by Lagenidium sp. in laboratory-reared larvae of the Dungeness crab,Cancer magister,and possible chemical treatments

A mycosis in larvae of the Dungeness crab, Cancer magister, was observed about 48 hr after they had molted to second-stage zoeae in the laboratory during a chronic bioassay. The fungus was of the genus Lagenidium and caused about 40% mortality of larvae before the test was terminated. Hyphal development and subsequent sporulation of the fungus was observed over a range of 0–32‰ salinity, with an optimum around 16‰. Bioassays of eight fungicides and the herbicide trifluralin, using the larvae and fungus in separate tests, were performed to explore means of chemical treatment. Trifluralin was the most satisfactory of the chemicals screened, with captan, Cu²⁺, and benomyl also giving good results for certain treatment intervals of up to 96 hr. Malachite green was toxic to larvae at concentrations inhibiting the fungus.     

Ontogeny of Behavior in the Crab Instars of the Dungeness Crab,Cancer magister Dana 1852

Schimpansen werden im Gombe-Nationalpark in Tansania seit 1960 beobachtet. Die Tiere bilden soziale Gruppen, die wir “Communities”, die Japaner “Unit-Groups” nennen. Als Faktoren, die von 1965 bis 1980 die Größe und Zusammensetzung der Hauptgruppe beeinflußten, werden erörtert: Pubertätsalter, Fortpflanzungsreife, Fortpflanzungszyklen der Weibchen, Geburtenfolge, Wechsel von Individuen zwischen Gruppen, Geschlechterverhältnis, Alterszusammensetzung und Mortalität. Zwischen 1970 und 1972 teilte sich die Gruppe. In den folgenden 5 Jahren wurden die Männchen und mindestens eins der Weibchen, die sich als Kahama-Gruppe abgespaltet hatten, von den Männchen der größeren Kasakela-Gruppe umgebracht. Eingehend werden Mortalitätsfaktoren (Krankheiten, Verletzungen, Mutterverlust, Alter) sowie der allgemeine Gesundheitszustand besprochen. Die deutlich unterschiedenen Regen- und Trockenzeiten im Gombe beeinflussen die Gesundheit und wohl auch die Fortpflanzung. In der Gruppe gibt es Inzucht, aber der Wechsel von Weibchen in andere Gruppen (der noch einigermaßen rätselhaft bleibt) sorgt für genetische Auffrischung. Die Befunde werden mit der einzigen anderen Langzeitstudie an freilebenden Schimpansen aus den Mahali-Bergen in Tansania verglichen. Der Einfluß künstlicher Fütterung in beiden Gebieten wird erörtert.     

A ciliate infection (Paranophrys sp.) in laboratory-held Dungeness crabs,Cancer magister

A ciliate infection ascribed to the genus Paranophrys was found in early adult Dungeness crabs, Cancer magister, held in laboratory bioassay facilities, and in outdoor flow-through tanks in Newport, Oregon. Infections proved lethal as ciliates multiplied to high densities in the blood and tissues causing degeneration and necrosis of musculature. All infected crabs had recent wounds through the exoskeleton which probably provided a portal of entry, and the elapsed time between infliction of a wound and gross symptoms of stress was estimated at 9 days although animals died as late as 26 days. The nature of Paranophrys infections in C. magister, i.e., as an opportunistic pathogen of cultured animals and/or a disease in wild populations of this crab is discussed.     

Quantification of responses from proprioceptive neurons in the limbs of the crab, Cancer magister.

In the limbs of crustaceans, proprioception is monitored by chordotonal organs. One in particular, MC1, is arranged in a manner that is accessible for single unit recording of primary sensory neurons while simulating joint movement. The movement-sensitive cells are of two types, those sensitive to relaxation or to elongation of the chordotonal strand which corresponds to flexion or extension of the meropodite-carpopodite joint, respectively. A statistical method for the quantification of these movement-sensitive proprioceptive neuronal responses was implemented. This statistical index, eta(2), should allow neuronal responses recorded in different laboratories to be easily and quantitatively compared. In addition, an eta(2) value can be assigned to individual cells which represents a cell's consistency and degree to which the response is related to the stimulus. We found some cells to have a high eta(2) and to be consistent in their activity while other cells had a high degree of variability with low eta(2) values. J. Exp. Zool. 284:629-636, 1999.     

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.     

Effects of high environmental ammonia on branchial ammonia excretion rates and tissue Rh-protein mRNA expression levels in seawater acclimated Dungeness crab Metacarcinus magister

In the present study of the marine Dungeness crabs Metacarcinus magister, the long term effects of high environmental ammonia (HEA) on hemolymph ammonia and urea concentrations, branchial ammonia excretion rates and mRNA expression levels of the crustacean Rh-like ammonia transporter (RhMM), H(+)-ATPase (subunit B), Na(+)/K(+)-ATPase (α-subunit) and Na(+)/H(+)-exchanger (NHE) were investigated. Under control conditions, the crabs' hemolymph exhibited a total ammonia concentration of 179.3±14.5μmol L(-1), while urea accounted for 467.2±33.5μmol L(-1), respectively. Both anterior and posterior gills were capable of excreting ammonia against a 16-fold inwardly directed gradient. Under control conditions, mRNA expression levels of RhMM were high in the gills in contrast to very low expression levels in all other tissues investigated, including the antennal gland, hepatopancreas, and skeletal muscle. After exposure to 1mmol L(-1) NH(4)Cl, hemolymph ammonia increased within the first 12h to ca. 500μmol L(-1) and crabs were able the keep this hemolymph ammonia level for at least 4 days. During this initial period, branchial RhMM and H(+)-ATPase (subunit B) mRNA expression levels roughly doubled. After 14 days of HEA exposure, hemolymph ammonia raised up to environmental levels, whereas urea levels increased by ca. 30%. At the same time, whole animal ammonia and urea excretion vanished. Additionally, branchial RhMM, H(+)-ATPase, Na(+)/K(+)-ATPase and NHE mRNA levels decreased significantly after long term HEA exposure, whereas expression levels of RhMM in the internal tissues increased substantially. Interestingly, crabs acclimated to HEA showed no mortality even after 4 weeks of HEA exposure. This suggests that M. magister possesses a highly adaptive mechanism to cope with elevated ammonia concentrations in its body fluids, including an up-regulation of an Rh-like ammonia transporter in the internal tissues and excretion or storage of waste nitrogen in a so far unknown form.     

Respiratory and digestive responses of postprandial Dungeness crabs, Cancer magister, and blue crabs, Callinectes sapidus, during hyposaline exposure

Respiratory responses and gastric processing were examined during hyposaline exposure in two crab species of differing osmoregulatory ability. The efficient osmoregulator, Callinectes sapidus, displayed an immediate increase in oxygen uptake when exposed to low salinity in isolation. In contrast, the weak osmoregulator, Cancer magister, showed no change in oxygen uptake upon acute exposure (<6 h), but slight increases in oxygen uptake tended to occur over longer time scales (12–24 h). These changes were likely attributable to an increase in avoidance activity after 6 h hyposaline exposure. Following feeding in 100% SW, oxygen uptake doubled for both species and remained elevated for 15 h. When postprandial crabs were exposed to low salinities, C. sapidus were able to sum the demands of osmoregulation and digestion. Thus, gastric processes continued unabated in low salinity. Conversely, postprandial C. magister prioritized responses to low salinity over those of digestion, resulting in a decrease in oxygen uptake when exposed to low salinity. This decrease in oxygen uptake corresponded to a reduction in the rate of contraction of the pyloric stomach and a subsequent doubling of gastric evacuation time. The current study is one of the few to illustrate how summation or prioritization of competing physiological systems is manifested in digestive processes.