Uca Pugilator Research Articles

Effects of Temperature and Water Loss on Terrestrial Locomotor Performance in Land Crabs: Integrating Laboratory and Field Studies

SYNOPSIS. Terrestrial and semi-terrestrial crustaceans are exposed to fluctuations in ambient temperature and conditions that favor evaporative water loss. These environmental stresses alter performance limits in the laboratory and behavior in the field. The maximal rate of oxygen consumption, maximum aerobic speed, and endurance capacity are greater at a body temperature (Tb) of 24°C than at 15°C or 30°C in the ghost crab, Ocypode quadrata . The total metabolic cost to move at the same relative speed is greater at a Tb of 24°C than at 15°C. Slower aerobic kinetics at 15°C result in a smaller relative contribution of oxidative metabolism to total metabolic cost. However, the relative contributions from accelerated glycolysis are similar at both temperatures. When locomotion is intermittent, the total distance traveled before fatigue can be similar at Tbs of 15 and 24°C but result from different movement and pause durations at these temperatures. Performance limits of the ghost crab are negatively affected by dehydration and are sensitive to rates of water loss. In the laboratory, endurance capacity of the fiddler crab, Uca pugilator, is greater at a Tb of 30°C than at 25°C. In the field, freely moving fiddler crabs with a Tb of 30°C travel at faster mean preferred speeds, as determined by motion analysis, than crabs at 25°C. Data for land crabs support and advance general ectothermic models for the effects of temperature and dehydration on locomotor performance.

Cloning of crustacean ecdysteroid receptor and retinoid-X receptor gene homologs and elevation of retinoid-X receptor mRNA by retinoic acid

We report the cloning and analysis of ecdysteroid receptor ( UpEcR) and retinoid-X receptor ( UpRXR) cDNA homologs from the fiddler crab Uca pugilator. The deduced amino acid sequence of this crustacean EcR most closely resembles the insect EcRs within the DNA binding and ligand binding domains (LBDs). For UpRXR, the DNA binding domain (DBD) shares greatest identity to the insect USPs. The ligand binding domain, however, is closer to vertebrate RXRs but may have a nonfunctional AF-2 domain. Probes derived from these clones were used to examine transcript levels in blastemas during early limb regeneration. Both UpEcR and UpRXR transcripts were detected in low amounts 1 day after limb loss, but increased during the next 4 days. Immersion of crabs in sea water containing all- trans retinoic acid increased the steady state concentrations of UpRXR transcript and altered the pattern of circulating ecdysteroids. These effects correlate with the disruptive effects of retinoic acid on blastemal differentiation observed in earlier studies.

Tissue-Specific Patterns and Steady-State Concentrations of Ecdysteroid Receptor and Retinoid-X-Receptor mRNA during the Molt Cycle of the Fiddler Crab,Uca pugilator

In the fiddler crab,Uca pugilator,we have investigated the temporal expression of receptors in various tissues using probes that encodeUcaecdysteroid receptor (UpEcR) and retinoid-X-receptor (UpRXR) gene homologs. During molt stages C4through D1–4,UpEcRandUpRXRtranscripts are expressed in regenerating limb buds, gills, eyestalks, hypodermis, hepatopancreas, muscle from nonregenerating walking legs, and the large cheliped. Some of these tissues have not previously been recognized as ecdysteroid-target tissues. Levels of ecdysteroids in the hemolymph fluctuate significantly during the molt cycle ofU. pugilator.The variation in steady-state concentrations ofUpEcRtranscripts in tissues from C4to D1–4implies molt cycle-related differences in the potential of these tissues to respond to changing titers of ecdysteroids in the hemolymph. In singly autotomized crabs, highest concentrations ofUpEcRtranscript in some tissues did not coincide with the highest levels of circulating ecdysteroids, suggesting thatUpEcRexpression in these tissues is not dependent on high ecdysteroid titers and may be induced by low or rising concentrations of ecdysteroids.UpEcRandUpRXRgenes were expressed simultaneously in tissues, supporting the possibility of heterodimerization for EcR and RXRin vivo.In some tissues, however, levels of transcripts differed, suggesting other possible receptor interactions. Moreover,UpEcRexpression in tissues from multiply autotomized crabs differed from the expression patterns in tissues from singly autotomized crabs.

Experimental transmission of white spot syndrome virus (WSSV) from crabs to shrimp Penaeus monodon.

White spot syndrome virus (WSSV) of the black tiger prawn Penaeus monodon is a recently discovered baculo-like virus disease which is currently the cause of very serious and widespread losses in the shrimp industry in Thailand and elsewhere in Asia. Three suspected crab carriers of this virus commonly found in shrimp-rearing areas were investigated. These were Sesarma sp., Scylla serrata and Uca pugilator. All these crabs could be infected with WSSV by injection and they sustained heavy viral infections for up to 45 d (confirmed by normal histology, specific in situ DNA hybridization and PCR amplification) without visible signs of disease or mortality. All of them also transferred the disease to P. monodon via water while physically separated in aquarium cohabitation tests. Transfer of the virus to the shrimp was monitored using in situ DNA hybridization and PCR assay at 12 h intervals after cohabitation began. With U. pugilator, WSSV could be detected in the shrimp cohabitants after 24 h using PCR amplification and after 60 h using in situ hybridization. With S. serrata, the shrimp were positive for WSSV after 36 h using PCR and after 60 h using DNA in situ hybridization. With Sesarma sp. they were positive after 48 h using PCR and 72 h using in situ hybridization. These laboratory studies demonstrated that crab carriers of WSSV may pose a real threat to cultivated shrimp. However, the studies were carried out in containers with a small volume and with relatively clean sea water as compared to shrimp cultivation ponds. Pond-based studies are now needed to determine whether factors such as pond volume, pond water quality and shrimp and crab behavior can influence the rate and success of transfer.

Prediction of maximum allowable retinal slip speed in the fiddler crab, Uca pugilator.

Stabilizing eye movements reduce movement of the image on the retina (retinal slip), and thus are assumed to improve visual acuity by reducing blur. The reasoning behind this argument is as follows. The response of individual photoreceptors (in the form of depolarization) to a brief flash of a given intensity is also brief. As is commonly observed in synaptic summation, the response to longer flashes is essentially a summation of many short-flash responses. After a period approximately equal to the duration of one short-flash response (T,), the summation ceases, and the response reaches a steady state. Prolonging the flash does not further depolarize the cell. I f a photoreceptor then samples a particular direction in space for more than T,, it gains no new information. Assuming no change in the intensity of incident light, this means that the eye does not lose spatial information if a retinal slip equal to one visual angle per T, (1,2) occurs. Here we present two measurements of the temporal dynamics of photoreceptors in the fiddler crab, Uca pugilator: T, and the frequency response. We will consider these in light of the theoretical allowable slip speeds for this animal. ERG measurements. The flash response time of Uca photoreceptors was estimated from ERG measurements after the crabs had been adapted for four hours to total darkness in the recording chamber. Light flashes (X = 570 nm, 1.25 pW/cm’) of increasing length were delivered at a frequency of 1 Hz, and the average amplitude of 15-20 ERGS was recorded. The flash duration at which the maximum ERG amplitude was reached and maintained for three consecutive measurements was taken as the length of the flash response for a dark-adapted eye. The flicker fusion frequency was measured with 10 ms flashes in dark adapted crabs, as well as in crabs adapted to and tested in 11.65 pW/cm’ fluorescent light. LED flashes of 570 nm, 10 ms long, were 1.25 pW/cm’ higher than adaptation and background intensity. Photoreceptor acceptance angle. This value, <, was estimated from the inter-ommatidial angle, A$,, which gives the spatial sampling frequency of the receptor array. The interommatidial angle was derived from pseudopupil mapping (3). While < for a given photoreceptor is not necessarily equivalent to a$~,,, it can be assumed for theoretical reasons to be close to but greater than A@, (4). The values of T, and < allow a conservative estimate of the highest retinal slip speed that does not decrease spatial acuity. This estimate is conservative because we have underestimated the 5 by using A&, and we have overestimated T, by using

Melatonin cycle in the fiddler crab Uca pugilator and influence of melatonin on limb regeneration.

Melatonin was measured over 24 hr in the eyestalks of Uca pugilator by means of radioimmunoassay; crabs were acclimatized either to a LD 12:12 photoperiod or constant darkness. A significant peak occurred at 13.00 hr in the LD 12:12 crabs. A photophase peak in melatonin has only been reported in one other species, also a crustacean. In constant darkness, two melatonin peaks occurred, one at 16.00 hr and the other 12 hr later; these results suggest that the melatonin cycle is a true circadian rhythm. HPLC with ultraviolet-visible detection was used to confirm the identity of melatonin immunoactivity. The influence of melatonin on regeneration of the walking legs was also examined: eyestalks were either removed or left intact, and limb bud length was measured every other day for at least 17 days in control and melatonin-treated crabs (60 microg ml(-1) seawater). Melatonin significantly increased the rate of limb regeneration in both eyestalk-intact and eyestalk-removed groups; this is contrary to results of regeneration studies in other phyla, in which similar melatonin concentrations inhibited regeneration.

Chelal Characteristics and Foraging Behaviour of the Blue CrabCallinectes sapidusRathbun

This paper describes the morphological and mechanical characteristics of the chelae ofCallinectes sapidus, together with the predation techniques, handling times and prey size selection of this voracious predator when presented with marsh mussels,Geukensia demissa, or fiddler crabs,Uca pugilator, in laboratory aquaria.Callinectes sapidusis heterochelous but differences in claw size and mechanical advantage between male and female crabs are statistically indistinguishable. Handling times for mussels and fiddler crabs increased steeply with prey size. Fiddler crabs are intrinsically more profitable than mussels, but the relative costs of capturing mobile prey, or excavating mussels, in natural populations is unknown. Previous laboratory experiments investigating the key stimuli used byC. sapiduswhen selecting prey are reviewed, and their results are compared with behaviour predicted by optimal foraging theory. It is concluded that crabs respond to the strongest stimuli received from the prey. Items were rejected after a given persistence time if the attack proved unsuccessful. Persistence time, however, was adjusted through experience to expectations of local prey quality and availability. The integrated result of this key-stimulus mechanism will be a close match to diets predicted by other behavioural models, including that based on optimal foraging theory.

Fiddler Crabs Use the Visual Horizon to Distinguish Predators from Conspecifics: A Review of the Evidence

Male fiddler crabs,Uca pugilator(Crustacea: Decapoda), respond to conspecifics by claw waving, and to predators by freezing or escape. In field experiments it was found that this distinction was not made on the basis of angular size and speed, nor was shape important. The remaining possibilities were either the absolute size of the stimulus, determined from angular size and distance, or the position of the stimulus relative to the horizon. To distinguish between these, a crab was placed in a glass dish, and moved black stimuli on a white background, at a distance of 22 cm. Stimuli below the crab's horizon hardly ever evoked escape. However, identical stimuli partially or wholly above the crab's horizon produced escape responses whose frequency varied with the angular size of the stimulus. Halving the distance of the stimulus showed that it was angular and not absolute size that determines escape frequency; and experiments with a tilted horizon showed that it is the position of the stimulus relative to the eye equator that is important, rather than the geographical horizon itself. It has been concluded that crabs categorize stimuli as dangerous or otherwise by their position relative to the crabs’ visual horizon.

Roles of neurotransmitters in regulating reproductive hormone release and gonadal maturation in decapod crustaceans

Summary Experiments done in this laboratory showed 5-hydroxytryptamine (5-HT) stimulates gonadal maturation in male and female sand fiddler crabs, Uca pugilator, and red swamp crayfish, Procambarus clarkii. This action of 5-HT is indirect, 5-HT apparently stimulating release of the gonad-stimulating hormone (GSH) that is present in the brain and thoracic ganglia. For example, studies with ovarian explants showed 5-HT has no direct effect on the ovary. But, when ovarian explants were incubated with 5-HT and brain or thoracic ganglia, the incubation medium produced greater ovarian maturation than did the medium when ovarian explants were incubated with brain or thoracic ganglia alone, 5-HT presumably enhancing GSH release. In males 5-HT not only induces testicular maturation but also development of the androgenic glands. 5-HT in males, as in females, apparently triggers GSH release; but in males GSH in turn stimulates the androgenic glands which release the androgenic gland hormone, resulting in testicular maturation. In contrast, dopamine (DA) inhibits gonadal maturation in both sexes. Methionine enkephalin, like DA, slows ovarian maturation. Red pigment-concentrating hormone (RPCH), like 5-HT, stimulates ovarian maturation both in vivo and in vitro, apparently by stimulating GSH release. RPCH does not affect the ovary directly. Calcium appears to act here as a second messenger for RPCH. The implications of these findings for enhancing the culture of crustaceans is discussed.

Effects of chemical cues on settlement behavior of blue crab Callinectes sapidus postlarvae

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 154:143-153 (1997) - doi:10.3354/meps154143 Effects of chemical cues on settlement behavior of blue crab Callinectes sapidus postlarvae Welch JM, Rittschof D, Bullock TM, Forward RB Jr Settlement of blue crab Callinectes sapidus Rathbun postlarvae (megalopae) was examined in the field in the presence and absence of chemical cues from settlement habitats and potential megalopal predators. Megalopae in premolt preferentially settled on collectors containing seagrasses Zostera marina and Halodule wrightii, but not on collectors with salt marsh cordgrass Spartina alterniflora. Settlement of megalopae was reduced by up to 40% in the presence of predators from several different habitats, including crabs Uca pugilator, U. pugnax and Panopeus herbstii, and grass shrimp Palaemonetes pugio. Laboratory predation assays showed that each of these potential predators ate C. sapidus megalopae if they encountered them. Megalopae avoided odors of U. pugilator in chemotaxis assays, and showed no reaction to odors from Z. marina and S. alterniflora. Settlement of megalopae was unaffected by the presence of adult C. sapidus or brown shrimp Penaeus aztecus, neither of which consumed megalopae in laboratory predation assays. Megalopae showed no reaction to fouled shells of oyster Crassostrea virginica, but avoided live C. virginica. Thus, settling blue crab megalopae can distinguish among settlement sites using chemical cues, and their discrimination ability increases in the premolt stage. Chemical cues · Settlement site selection · Callinectes sapidus · Megalopae · Post-<\n>larvae · Eelgrass · Predators · Chemotaxis · Blue crab Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 154. Publication date: July 31, 1997 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1997 Inter-Research.

Expression of the genes encoding the ecdysteroid and retinoid receptors in regenerating limb tissues from the fiddler crab, Uca pugilator

Using sequence information derived from the Drosophila melanogaster (Dm) ecdysteroid receptor (EcR)- and retinoid X receptor (RXR)-encoding gene homologs; we have isolated cDNA clones corresponding to the DNA-binding domains (DBD) for these two nuclear receptors from the fiddler crab, Uca pugilator (Up). Both genes appear to be represented in 1–2 copies in the Up genome, and unlike Dm, contain an intron within the DBD-encoding region. Sequence comparisons to the Dm EcR and RXR homologs indicate 76 and 82% nucleotide identity, respectively, corresponding to 6 and 4 single-amino acid substitutions which primarily cluster in the region of the molecule involved in dimerization. RT-PCR analysis indicates that both the EcR and RXR homologs are expressed during the initial stages of limb regeneration, temporally concomitant with early blastema formation and the secretion of a flexible sac cuticle at the site of limb loss.

Substrate Recognition by Recombinant Serine Collagenase 1 from Uca pugilator

Uca pugilator serine collagenase 1 was cloned and sequenced from a fiddler crab hepatopancreas cDNA library. A full-length sequence encodes a 270-amino acid pre-pro-enzyme highly identical in structure to the chymotrypsin family of serine proteases. The zymogen form of the enzyme was expressed in Saccharomyces cerevisiae as a fusion with the alpha-factor signal sequence under control of the alcohol dehydrogenase/glyceraldehyde-3-phosphate dehydrogenase promoter. Upon activation with trypsin, the recombinant collagenase possesses collagenolytic properties identical to those of the enzyme isolated from the crab hepatopancreas. The collagenase substrate binding pocket recognizes a wide range of basic, hydrophobic, and neutral polar residues. beta-Branched and acidic amino acids are poor substrates. Acylation is rate-limiting for collagenase versus peptidyl amides, rather than deacylation, as for trypsin and chymotrypsin. Correlations relating substrate volume and hydrophobicity to catalysis were found for collagenase and compared to those for chymotrypsin and elastase. Relative enzyme efficiencies on single amino acid versus tetrapeptide amide substrates show that collagenase derives less catalytic efficiency from binding of the primary substrate residue than trypsin or chymotrypsin, but compensates in binding of the extended peptidyl residues. Serine collagenase 1 is a novel member of the chymotrypsin protease family, by virtue of its amino acid sequence and multifunctional active site.

Cadmium and naphthalene-induced hyperglycemia in the fiddler crab, Uca pugilator: differential modes of action on the neuroendocrine system.

Hyperglycemia is a typical response of aquatic organisms to heavy metals. In crustaceans, the medulla terminalis X-organ-sinus gland neuroendocrine complex in the eyestalk is the source of the crustacean hyperglycemic hormone (CHH). The role of CHH in pollutant-induced b1ood glucose changes has only recently begun to be studied. Reddy provided evidence that CHH mediates cadmium-induced hyperglycemia in the red swamp crayfish, Procambarus clarkii. In a study of another hormonally-regulated function, color changes, cadmium exposure resulted in pigment in the melanophores of the fiddler crab, Uca pugilator, becoming less dispersed than in unexposed crabs. Earlier studies showed that, like cadmium, both a PCB, Aroclor 1242, and naphthalene induced black pigment aggregation in Uca poor. In general, when crabs are exposed to a pollutant, hydrocarbon or cadmium, they aggregate the pigment in their melanophores, but apparently by different mechanisms. Hydrocarbons appear to inhibit release of black pigment-dispersing hormone (BDPH), whereas cadmium appears to inhibit its synthesis. These apparent different modes of action of cadmium and naphthalene on the color change mechanism led us to compare the impact of these pollutants on the hormonal regulation of blood glucose in Uca pugilator. The present study was performed to determine (1) whether cadmium and naphthalenemore » induce hyperglycemia in Uca pugilator, (2) whether CH has a role, if naphthalene and cadmium do induce hyperglycemia, and (3) the effects, if any, of cadmium and naphthalene on CHH activity in the eyestalk neuroendocrine complex.« less

Isolation and characterization of sinus gland neuropeptides with both mandibular organ inhibiting and hyperglycemic effects from the spider crab Libinia emarginata

Using two-step reverse phase HPLC, we isolated and purified three peptides with mandibular organ inhibiting hormone (MO-IH) activity from the spider crab Libinia emarginata. One of the peptides, P22, gave a yield of 355 ng/SG. The others gave lower yields: P21, 9 ng/SG; P25, 67.5 ng/SG. The molecular weight was determined to be 8,439 for P25, 8,474 for P22, and 8,398 for P21 by mass spectrometry. All three peptides have similar amino acid compositions and contain 72–76 residues. We believe these peptides to be different isoforms of one family. The MO is more sensitive to the two minor isoforms, P21 and P25. All three isoforms can inhibit MO activity to a maximum inhibition of 70%. All three isoforms gave a significant hyperglycemic effect when injected into de-eyestalked fiddler crabs Uca pugilator. We believe the MO-IHs to be members of the crustacean hyperglycemic hormone (CHH) family, having similar amino acid compositions and both biological activities. © 1996 Wiley-Liss, Inc.

Isolation and characterization of sinus gland neuropeptides with both mandibular organ inhibiting and hyperglycemic effects from the spider crabLibinia emarginata

Using two-step reverse phase HPLC, we isolated and purified three peptides with mandibular organ inhibiting hormone (MO-IH) activity from the spider crab Libinia emarginata. One of the peptides, P22, gave a yield of 355 ng/SG. The others gave lower yields: P21, 9 ng/SG; P25, 67.5 ng/SG. The molecular weight was determined to be 8,439 for P25, 8,474 for P22, and 8,398 for P21 by mass spectrometry. All three peptides have similar amino acid compositions and contain 72–76 residues. We believe these peptides to be different isoforms of one family. The MO is more sensitive to the two minor isoforms, P21 and P25. All three isoforms can inhibit MO activity to a maximum inhibition of 70%. All three isoforms gave a significant hyperglycemic effect when injected into de-eyestalked fiddler crabs Uca pugilator. We believe the MO-IHs to be members of the crustacean hyperglycemic hormone (CHH) family, having similar amino acid compositions and both biological activities. © 1996 Wiley-Liss, Inc.

Plasticity in reproductive timing by crabs in adjacent tidal regimes

Author(s): Morgan, SG | Abstract: Tidal variation may cause reproductive timing by fiddler crabs Uca pugilator (Bosc) to vary geographically and seasonally. Fiddler crabs in a semidiurnal tidal regime along the Atlantic coast of the USA were previously shown to release larvae synchronously during maximum amplitude evening high tides near new and full moons throughout the reproductive season. In the present study, fiddler crabs in a diurnal tidal regime on the Gulf coast of the USA released larvae during intermediate amplitude flood tides near dawn regardless of lunar phase throughout most of the reproductive season. Late in the summer, peak larval release occurred near maximum amplitude high tides as on the Atlantic coast. In a mixed semidiurnal tidal regime on the Gulf coast, peak larval release by fiddler crabs occurred during intermediate amplitude high tides near dawn, but biweekly periodicity was weak late in the reproductive season. Intraspecific variation in reproductive timing arose because nocturnal maximum high tides did not occur along the Gulf coast during most of the summer, but these tides returned during late summer in the diurnal tidal regime. Reproductive timing changed concomitantly with changing phase relationships of tides with light-dark and lunar cycles. Variation in reproductive timing is phenotypic because crabs that were translocated reciprocally between diurnal and mixed semidiurnal tidal regimes entrained to the timing patterns of local crabs. A hierarchy of rhythms regulating reproductive timing was revealed by the degree to which larval release kept phase with lunar, tidal amplitude, tidal and light-dark cycles. These hierarchies enabled crabs to track phase shifts of cycles in variable tidal environments and may enhance mean reproductive success throughout the range of the species.

Inhibition of acetylcholinesterase activity in the central nervous system of the red swamp crayfish, Procambarus clarkii, by mercury, cadmium, and lead.

The toxicological, physiological and biochemical responses of aquatic crustaceans to heavy metals have been reported by several investigators. Levels of glucose, lactic acid, sodium, potassium, aspartate aminotransferase and alanine aminotransferase in the blood of the crab Scylla serrata increased, while glycogen levels in hepatopancreas and muscle decreased after a four-week exposure to mercuric chloride. In fiddler crab, Uca pugilator, enzyme activity was observed to decrease in the hepatopancreas but increased in abdominal muscle after 48 hr cadmium exposure. In the red swamp crayfish, Procambarus clarkii, exposed for 96 hr to cadmium, glutahione (GSH) level and GSH S-transferase activity deceased in the midgut. In crayfish Astacus astacus exposed to sublethal concentrations of lead and cadmium, oxidative enzyme (succine dehydrogenase and NADPH-cytochrome P450 reductase) activities in gills and hepatopancrease decreased. Acetylcholinesterase (AChE) inhibition by organophosphates and organocarbamates in various crustaceans has bee reported. In vivo cadmium exposure caused increases in esterase activities, but mercury exposure decreases these activities in the hepatopancreas of the shrimp Callianassa tyrrhena. The freshwater crab, Barytelphusa guerini, exposed to 0.6 ppm cadmium showed reduced oxygen consumption throughout the experiment whereas AChE activity increased after 4 days but decreased after 15 days. The authors wanted to determine the effectsmore » of cadmium, lead and mercury on AChE activity in central nervous tissue of Procambarus clarkii. This enzyme has the potential for serving both as a biochemical indicator of toxic stress and a sensitive parameter for testing water for the presence of toxicants. These three biologically silent metals have, according to Schweinsberg and Karsa great toxicological significance to humans because their use is widespread. 14 refs., 4 figs.« less

Effects of all‐trans retinoic acid on regenerating limbs of the fiddler crab,Uca pugilator

AbstractRegeneration of walking legs in the fiddler crabUca pugilatorrepresents true epimorphic growth since it involves organization of an undifferentiated blastema prior to regrowth of a new limb. Normal regeneration inUcaconsists of two major stages—basal growth and proecdysial growth. One of the earliest events in the basal growth stage of regeneration is the secretion of cuticle by epidermal cells that migrate under the scab at the site of limb loss. When crabs are maintained in a 0.05 mM emulsion of retinoic acid (RA) in sea water during the first 2 weeks following autotomy, the pattern of cuticle secretion is disrupted in many limb buds. Limb buds on RA‐treated crabs grow more slowly and are frequently malformed. © 1995 Wiley‐Liss, Inc.

The visual control of behaviour in fiddler crabs

The distribution of resolution around the eye of the fiddler crab Uca pugilator was measured using the pseudopupil, and the results were compared with various behavioural thresholds. As noted previously (Zeil et al. 1986) the eye has a band of greatly increased vertical resolution around the middle with inter-ommatidial angles as small as 1° (Figs. 1–3). In life this band images the horizon. The horizontal resolution is nearly constant throughout the eye. Males notice females when they subtend 2 to 3 inter-ommatidial angles, and distinguish males from females when they subtend 6 to 7 ommatidia (Fig. 6). Potential predators are detected when they subtend only one inter-ommatidial angle, and move through a similar angle. Using models, it was found that males respond to moving objects of the right size as though they were conspecifics, although they do not resemble crabs in shape. It is concluded that only one feature distinguishes other crabs from predators: whether they appear below or above the crab's horizon.

Evidence for opioid involvement in the regulation of ovarian maturation of the fiddler crab, Uca pugilator

Abstract The potential involvement of an endogenous opioid system in the regulation of ovarian development in the fiddler crab, Uca pugilator, was investigated in vivo. Injection of the opioid, methionine enkephalin, into female crabs significantly slowed ovarian maturation in a dose-dependent manner. In contrast, injection of the opioid antagonist, naloxone, produced dose-dependent ovarian maturation. These results provide the first evidence that an opioid system is involved in the control of reproduction in a crustacean. It is hypothesized that the opioid (a) stimulates release of the gonad-inhibiting hormone, (b) inhibits release of the gonad-stimulating hormone or (c) does both (a) and (b).