Fiddler Crab Uca Pugilator Research Articles

Vibration transmission through the walking legs of the fiddler crab,Uca pugilator (Brachyura, Ocypodidae) as measured by Laser Doppler Vibrometry

1. Substrate-borne vibration signals play an important role in the life of the fiddler crabUca pugilator. In this study we investigated how a vibration signal is transmitted through the legs and body of the freely standing live crab and how it is modified on its way to the sites of the crab's vibration-receptive organs. 2. An optical technique, Laser Doppler Vibrometry (LDV), was used to measure the motion of the substrate (the input signal) and the motion of the dactylopodite, carpopodite, meropodite and carapax (the output signals). The output motion was compared with the input motion to determine the transfer function at each of the measured points over the frequency range of 10 to 1,000 Hz. 3. In response to a single input vibration pulse with an energy spectrum similar to that of a rap of a male fiddler crab, points on the crab showed amplification of the low-frequency components (up to 25–250 Hz) with no amplification or else attenuation in a mid-frequency range (from 25–250 to about 800 Hz), and then a range of less attenuation or slight amplification above about 800 Hz (Fig. 4). The amplification and attenuation effects tended to be more pronounced the further away from the leg tip the measurement point was. Maximal low-frequency amplification ranged from 8 to 32 dB, maximal mid-frequency attenuation between −7 and −33 dB, with higher values closer to the carapax. The vibration transfer characteristics were essentially independent of the input amplitude over the biologically relevant intensity range (Fig. 5). 4. When a train of input pulses was given at about the drumming rate of maleUca pugilator the transfer function changed during the train, with transmission of the first few impulses being as described above and that of later impulses being more ‘sharply tuned’, that is, with the low-frequency amplification range being narrower (Fig. 6). This change in transmission is reproducibly accompanied by small active postural changes of the crab (‘alerting reaction’). 5. Animals resting in body-contact with the substrate rather than in an upright ‘alert’ stance showed very different transmission characteristics with much less modification of the signal between substrate and carapax (Fig. 7). 6. These results are compared with the known spectral energy distribution of crab drumming signals. It is concluded, that the described transmission characteristics of the crab leg emphasize the specific communication signals while at the same time damping noise vibrations.

Neuroendocrine control of Na+ balance in the fiddler crab Uca pugilator.

The hemolymph ionic composition and unidirectional Na+ fluxes were analyzed in fiddler crabs (Uca) acclimated to 500 mosmol seawater. Eyestalkless crabs had lower hemolymph osmotic, Na+, and Cl- concentrations. The Na+ efflux was increased from 13.6 +/- 0.6 in control crabs to 19.6 +/- 1.3 mueq.g-1.h-1 in eyestalkless crabs; this increase was shown to be due to a higher Na+ permeability in eyestalkless crabs. Hemolymph Na+ in eyestalkless crabs was increased by an injection of eyestalk extract. The Na+ influx was increased from 11.1 in intact to 15.8 mueq.g-1.h-1 in eyestalkless animals. A kinetic study showed that 1) the influx was higher at all external Na+ concentrations in eyestalkless and intact-Na+-depleted crabs than in intact controls, and 2) the influx mechanism exhibited allosterism. The elevated Na+ influx in eyestalkless crabs was decreased by an injected eyestalk extract. An injected brain extract caused in increase in the Na+ influx in intact animals. It is concluded that the Na+ uptake mechanism is activated by decreasing the hemolymph Na+ concentration and that a brain hormone mediates the effect.

Experimental studies of particle ingestion by the sand fiddler crab Uca pugilator (Bosc)

Particle ingestion by the sand fiddler crab Uca pugilator (Bosc) was investigated using clean sand sediment inoculated with glass and plastic beads. For all bead types, the number ingested was positively correlated with the initial sediment bead concentration. Ingestion efficiency, however, was inversely correlated with bead diameter, weight, and initial sediment bead concentration. The latter result suggests that the particle sorting mechanism can be saturated at high substratum particle concentrations. Crab size was directly related to the efficiency at which large beads were ingested, but had no effect on the ingestion of small beads. Ciliates, unbound bacteria, and bacteria attached to sand grains were ingested with high efficiency, but the crabs did not preferentially ingest live over inert particles. Other results suggest that maximization of food intake by sand fiddlers occurs at the habitat patch level rather than at the level of particle ingestion. Supporting this view is the observation that inert particles which were ingested with high efficiencies did not stimulate crab feeding. Sediment harvesting rates were inversely related to substratum organic and silt concentrations suggesting that sand fiddlers can control ingestion rates by regulating sediment harvesting rates

Pharmacological Evidence for Involvement of Presynaptic Alpha2 Adrenoceptors in Norepinephrinergic Neurotransmission Triggering the Release of Melanin-dispersing Hormone in the Fiddler Crab Uca Pugilator

ABSTRACT 1. The specific alpha2 adrenoceptor agonist B-HT 933 significantly reduced the rate of melanin dispersion in crabs transferred from a white to a black background. 2. The specific alpha2 adrenoceptor blockers rauwolscine and yohimbine significantly increased the rate of melanin dispersion in crabs transferred from a white to a black background. 3. Rauwolscine and yohimbine, but not the alpha, adrenoceptor blocker indoramin, antagonized B-HT 933. 4. In crabs pretreated with the catecholaminergic neurotoxin 6-hydroxydopamine, which inhibits melanin dispersion, B-HT 933 did not produce further significant inhibition in the rate of melanin dispersion. 5. None of the drugs has been found to affect melanin migration in melanophores of isolated legs. 6. The results are consistent with the hypothesis that presynaptic adrenoceptors very similar to alpha2 adrenoceptors of mammals regulate impulse-mediated norepinephrinergic neurotransmission in the fiddler crab Uca pugilator, norepinephrine triggering release of a melanin-dispersing hormone.

Deposit-feeding by the ghost crab Ocypode quadrata (Fabricius)

Observations using a videotape system on a secluded, Georgia, barrier beach revealed that the ghost crab Ocypode quadrata (Fabricius) exhibits diurnal deposit-feeding behavior similar to that manifested by the sand fiddler crab Uca pugilator (Bosc). The only other ghost crabs reported to engage in deposit-feeding, Ocypode ceratophthalma and guadichaudii, use their chelae in a different manner than O. quadrata or Uca pugilator. Ocypode quadrata individuals collect more substratum per feeding motion and produce larger feeding pellets, aggregations of harvested but uningested substratum, than do sand fiddlers. The difference in feeding pellet size appears to be related to differences in buccal cavity size. Differences in Chl a concentrations between feeding pellets and unforaged substratum showed that O. quadrata is less efficient than Uca pugilator at extracting algae from the harvested substratum. However, ghost crabs can extract up to 70% of the available algae. Findings of this study suggest that deposit-feeding is an important adjunct to predatory behavior.

Effects of Norepinephrine and Norepinephrine Agonists and Antagonists on the Melanophores of the Fiddler Crab Uca Pugilator

Norepinephrine produces dose-related pigment dispersion in the melanophores of intact and eyestalkless fiddler crabs, Uca pugilator, but has no effect on the melanophores in isolated legs. 2. The effects of agonists and antagonists of norepinephrine on the rates of melanin dis- persion and concentration were determined. 3. The results are consistent with the hypothesis that norepinephrine exerted its effect by acting on the central nervous system to trigger the release of melanin-dispersing hormone. Migration of the pigment in the chromatophores of the fiddler crab Uca pugi- lator is hormonally regulated (Carlson, 1935; Sandeen, 1950; Brown, 1950; Fin- german, 1956a). A series of experiments performed with this crab has revealed that release of red pigment-dispersing hormone is triggered by 5-hydroxytrypt- amine (=serotonin) (Rao and Fingerman, 1970b) whereas release of red pigment- concentrating hormone is triggered by dopamine (Fingerman and Fingerman, 1977). However, no one has as yet identified a neurotransmitter substance which appears to be involved in triggering release of melanin-dispersing hormone (MDH), melanin-concentrating hormone (MCH), white pigment-dispersing hor- mone, or white pigment-concentrating hormone in any species of fiddler crab. Abramowitz and Abramowitz (1938) tested both acetylcholine and epinephrine on melanophores of Uca pugilator, and reported that they had no effect in either producing dispersion or aggregation of the pigment in these cells. Although Bau- chau and Mengeot (1966) found that 5-hydroxytryptamine will produce dispersion of the pigment in the melanophores of the shore crab Carcinus maenas, Rao and Fingerman (1970a) observed that this compound has no such effect on the me- lanophores of Uca pugilator. Presented below are the results of a series of ex- periments which led to identification of norepinephrine as a neurotransmitter substance that appears to be involved in triggering release of MDH in Uca pu- gilator. Experiments were also performed to identify a neurotransmitter sub- stance that might be involved in release of white pigment-dispersing hormone, but these were unsuccessful.

Effect of zinc on regeneration in the fiddler crab Uca pugilator and its interactions with methylmercury and cadmium

After multiple autotomy (one chela and six walking legs) fiddler crabs ( Uca pugilator) were exposed to zinc chloride, cadmium chloride, methylmercuric chloride or combinations of these metals. Zinc at 1, 3 and 5 ppm had a retarding effect on limb regeneration, which was amplified in water of reduced salinity. Methylmercury at 0·5 ppm and cadmium at 1·0 ppm have previously been found to retard regeneration. When crabs were exposed to meHg and Zn the effects were additive, both in sea water (30% salinity) and in water of reduced salinity (7–8%). However, when crabs were exposed to combinations of Zn and Cd the effects were antagonistic and the rate of regeneration was almost that of controls. In water of 7–8% salinity the Cd effect was greatly intensified and growth was almost totally prevented. The presence of Zn counteracted this and allowed growth and ecdysis to occur.

Experimental studies on the foraging behavior of the sand fiddler crab Uca pugilator (Bosc, 1802)

The purpose of this study was to test the hypothesis that foraging sand fiddler crabs. Uca pugilator (Bosc), move through the habitat in response to low substratum food levels even though these movements may take the crabs considerable distances from the safety of the burrow area. Chl a and ATP concentrations were used as measures of food density in foraged and unforaged substratum. Field and laboratory feeding experiments showed that crab foraging intensity in a habitat patch was directly correlated with food density in the patch either in the presence or absence of alternative food patches. Other experiments showed that sand fiddlers can respond to differences in food level on a scale of millimeters and do this by probing the substratum with minor chelae. Food levels in aggregations of non-ingested particles harvested by sand fiddlers, feeding pellets, correspond to low foraging intensities predicted from foraging experiments and crabs exhibit low foraging intensities on substratum patches derived from feeding pellets. Substratum food levels in two distinct areas corresponded to high predicted foraging intensities and there was no consistent trend in the level of food in the burrow vs. the nonburrow microhabitats. These results suggest that the movements of foraging sand fiddlers are to some extent controlled by the reduction in substratum food levels due to feeding during a single foraging episode. Sand fiddlers can extract over 70% of the food from harvested substratum over a broad range of substratum food densities but harvest only 42% of the available substratum.

Chemical and Enzymatic Characterization of the Collagenase from the Insect Hypodearma lineatum

The collagenase from the larvae Hypoderma lineatum, with a molecular weight of 24 000 and isoelectric point of 4.1, was obtained in homogeneous form by ion-exchange chromatography. It is stoichiometrically inhibited by diisopropylfluorophosphate. On the other hand it is unaffected by ethylenediaminetetraacetate, p-chloromercuribenzoate, dithiothreitol, N-tosyllysine chloromethyl ketone, N-tosylphenylalanine chloromethyl ketone and ovomucoid trypsin inhibitor. The enzyme which degrades native collagen in its helical parts, has a specific activity on thermally reconstituted collagen fibrils of 150 micrograms collagen degraded x min-1 x (mg enzyme)-1 at 37 degrees C. It hydrolyses casein but has no esterolytic activity characteristic of trypsin, chymotrypsin nor elastase. It has no action on the synthetic peptide 4-phenylazobenzyloxycarbonyl-L-prolyl-L-leucyl-L-glycyl-L-prolyl-D-arginine. The amino acid composition of Hypoderma collagenase indicates a distinct similarity with the serine proteinases of the trypsin family and with another athropode serine collagenase, that of the fiddler crab Uca pugilator. This suggests that eucaryotic collagenases with digestive rather than morphogenic function represent a new category of members of the trypsin family.

Interactions of methylmercury, cadmium, and salinity on regeneration in the fiddler crabs Uca pugilator, U. pugnax and U. minax

After multiple autotomy in the fiddler crabs Uca pugilator, U. pugnax and U. minax, both methylmercury and cadmium retard limb regeneration and ecdysis. When crabs in sea water are exposed to a mixture of both metals, the effect is increased, indicating that the two are interacting in an additive way. In 50% sea water (=15% S), the effects of cadmium are greatly intensified so that growth of limb buds is extremely slow, if it occurs at all. When methylmercury is present in the water at the same time, the severe effects of cadmium are somewhat ameliorated, indicating an antogonistic interaction of the two metals under these conditions. Adding additional calcium to the 50% sea water also decreased the severity of the cadmium effect, thus supporting the idea of a calcium-cadmium competition.

Metabolic response to thermal changes of the adult fiddler crab Uca pugilator and the effect of PCBs

Although polychlorinated biphenyls (PCBs) are widespread in the environment, their influence on functional characteristics of marine animals is poorly known. This paper presents data on the relative effects of a sublethal concentration (50 ppb) of Aroclors® 1016 and 1254 on the respiratory metabolism of the fiddler crab Uca pugilator (Bosc.), an intertidal, estuarine inhabitant. At 25°C, the respiration rate of both males and females increased initially after exposure to these Aroclors. After the crabs were returned to uncontaminated seawater, their respiratory rates were similar to initial pre-exposure values. At 15°C, Aroclors 1016 and 1254 had no apparent effect on the respiration of males but depressed that of females. Upon exposure to PCB-free seawater, the metabolic rate of both male and female crabs was similar to initial pre-exposure rates. At 35°C, a trend existed for both of these PCBs to inhibit respiration. In a series of experiments on cold- and warm-acclimated individuals, PCBs did not consistently influence metabolic response over the thermal range of 10° to 30°C.

Influence of the polychlorinated biphenyl preparation Aroclor 1242� on color changes of the fiddler crab Uca pugilator

The melanin in the melanophores of specimens of the fiddler crab, Uca pugilator, exposed to 2, 4, and 8 ppm solutions of the polychlorinated biphenyl (PCB) preparation, Aroclor 1242®, became less dispersed than in untreated specimens. This effect was dose-dependent. It was probably due to the PCB itself and not to polychlorinated dibenzofurans which are contaminants of commercial PCBs. The decreased melanin dispersion appeared to be related to a decrease in the rate of release of melanin-dispersing hormone from eyestalk neuroendocrine cells into the hemolymph. Eyestalks of crabs kept for 4 days in Aroclor 1242 contained 4 times as much melanin-dispersing hormone as did control crabs. When injected into isolated legs, did hemolymph from control crabs. Aroclor 1242 did not appear to have a direct effect on the pigment-dispersing mechanism of the melanophores.

Feeding experiments on the larvae of the fiddler crab Uca pugilator (Brachyura, Ocypodidae), reared in the laboratory

Larvae of Uca pugilator (Bosc) were reared in the laboratory from hatching to the megalopa stage on three different diets: (1) newly hatched Artemia salina nauplii (diet A), (2) the rotifer Brachionus plicatilis (O.F. Müller) and a ciliate Euplotes sp. (diet RC), and (3) a combination of the above two diets (diet ARC). The survival rate of zoeae fed diet A (90.0%) and diet ARC (93.8%) was much higher than that of the larvae fed diet RC (22.5%). The duration of the zoeal stages was significantly shorter for the larvae fed diet ARC than for those fed diets A and RC. The survival rate of megalopa larvae (reared on diets A and ARC in the zoeal stages) was high (above 90%) for megalopa fed Artemia nauplii only, as well as for those fed a combination of Artemia nauplii and shrimp. No significant differences in duration of the megalopa stage were found between the latter diet groups.

A bacterial infection in the common shore crab Carcinus maenas and the fiddler crab Uca pugilator

A bacterial infection in Carcinus maenas and in Uca pugilator is described. The percentage of infections recorded in the field was between 0 and 10%, depending on season. Infected crabs remain about 3 times longer in Intermolt Stages C3 and C4 than do healthy crabs. In infected specimens of both species, the glucose level in the hemolymph is increased and protein, copper and lipid concentrations in the hemolymph as well as the glycogen content of various tissues are diminished. The coagulation process is disturbed in infected crabs. The hemocytes aggregate, but the formation of fibrin-like fibers, which can be observed in healthy crabs, does not occur.

Hormonal involvement in thermal acclimation in the fiddler crab Uca pugilator (BOSC)—II. Effects of extracts on tissue respiration

1. 1. A factor is present in cold-acclimated crabs which significantly increases respiration in tissues from warm-acclimated animals. 2. 2. Activity was present in extracts of the supraesophageal ganglion and the sinus gland, but not in extracts of sinus-glandless eyestalks. 3. 3. Ethanol extracts showed greater respiration-enhancing activity than saline extracts. Activity decreased after extracts were heated and disappeared after treatment of the extracts with pronase.

The presence of 5-hydroxytryptamine in the eyestalks and brain of the fiddler crab Uca pugilator, its quantitative modification by pharmacological agents, and possible role as a neurotransmitter in controlling the release of red pigment-dispersing hormone

The presence of 5-hydroxytryptamine in the eyestalks and brain of the fiddler crab Uca pugilator, its quantitative modification by pharmacological agents, and possible role as a neurotransmitter in controlling the release of red pigment-dispersing hormone

The presence of 5-hydroxytryptamine in the eyestalks and brain of the fiddler crab UCA pugilator, its quantitative modification by pharmacological agents, and possible role as a neurotransmitter in controlling the release of red pigment-dispersing hormone

Abstract 1. 5-Hydroxytryptamine (5-HT, serotonin) is present in the eyestalks (7.38–7.63 μ g./g. wet weight) and brain (2.77–3.38 μ g./g. wet weight) of the fiddler crab Uca pugilator . 2. Reserpine and 5,6-dihydroxytryptamine produced a decrease in the 5-HT levels of both the eyestalks and brain. Both drugs also caused concentration of the red chromatophoric pigment. 3. Injection of pargyline, a monoamine oxidase inhibitor, resulted in an increase in the 5-HT content of both the eyestalks and brain. This drug evoked dispersion of the red chromatophoric pigment. 4. Bilateral eyestalk ablation resulted in an increase of the 5-HT level of the brain. 5. These results are consistent with the hypothesis that 5-HT has a normal role in the fiddler crab as a neurotransmitter involved in stimulating the release of red pigment-dispersing hormone.

Synergistic effects of environmental variables on larvae of Uca pugilator

The effects of sublethal concentrations of mercury in combination with stressful temperature-salinity regimes were considered for larval development of the fiddler crab Uca pugilator (Bosc.). Control organisms were compared to those treated with 1.8 ppb Hg for the following suboptimal regimes: 30°C, 30 ‰ S; 30°C, 20 ‰ S; 20°C, 30 ‰ S, and 20°C, 20 ‰ S. As physiological indicators of larval response, the survival rate, the O2 consumption rate, and phototactic response were measured, following either acute 24 h doses of Hg, or chronic rearing in Hg. All response parameters were modified in larvae maintained under the suboptimal conditions; mercury compounded the effects.

Behavior of chromatophores of the fiddler crab Uca pugilator and the dwarf crayfish Cambarellus shufeldti in response to synthetic Pandalus red pigment-concentrating hormone

Synthetic Pandalus red pigment-concentrating hormone was effective in concentrating the pigment in the erythrophores of the fiddler crab Uca pugilator and the dwarf crayfish Cambarellus shufeldti. However, this hormone had no effect on the melanophores of the crab or the leucophores of the crab and crayfish. These results are in accord with the hypothesis that in the fiddler crab and the dwarf crayfish, respectively, the hormonal control for each type of chromatophore is different.

COMPARISON OF THE PIGMENTARY EFFECTOR TROPINS IN THE EYESTALKS AND ABDOMINAL NERVE CORD OF THE PRAWNPALAEMONETES VULGARIS

1. Extracts of the eyestalks and abdominal nerve cords of the prawn Palaemonetes vulgaris were chromatographed on Bio-Gel P-6. The fractions of both extracts revealed melanin-dispersing activity in the fiddler crab Uca pugilator and red and white pigment-dispersing activities and distal retinal pigment light-adapting activity in the prawn. In addition, the eyestalk fractions contained red and white pigment-concentrating activities whereas only the red pigment-concentrating activity was found in the fractions of the abdominal nerve cords.2. The pigment-dispersing and distal retinal pigment light-adapting activities were eluted from the column ahead of the pigment-concentrating activities and were consequently separated from them. However, the pigment-dispersing and distal retinal pigment light-adapting activities did not separate from each other. The pigment-concentrating activities likewise did not separate from each other.3. The substance from the prawn which evokes melanin dispersion in the fiddler crab is not the substance that causes red pigment dispersion and perhaps white pigment dispersion as well in the prawn itself.4. Furthermore, dispersion of the red and white chromatophoric pigments in the prawn is not caused by the substance that evokes light adaptation of its distal retinal pigment.5. Evidence is presented to support the hypothesis that light-adaptation of the distal retinal pigment in Palaemonetes is caused by the substance found in the prawn that causes melanin dispersion in the fiddler crab. Palaemonetes itself lacks melanophores.