Showing papers on "Uca pugilator published in 1997"

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

Abstract: 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 ...

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

Abstract: 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.

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

Abstract: Tilden AR, Rasmussen P, Awantang RM, Furlan S, Goldstein J, Palsgrove M, Sauer A. Melatonin cycle in the fiddler crab Uca pugilator and influence of melatonin on limb regeneration. J. Pineal Res. 1997; 23:142–147. © Munksgaard, Copenhagen Abstract 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 μg 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

Abstract: This paper describes the morphological and mechanical characteristics of the chelae of Callinectes 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 sapidus is 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 by C. sapidus when 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.

Effect of Cadmium Chloride on the Distal Retinal Pigment Cells of the Fiddler Crab, Uca pugilator

Abstract: Crustaceans have two sets of pigmentary effectors, chromatophores and retinal pigment cells. Retinal pigments control the amount of light striking the rhabdom, the photosensitive portion of each ommatidium, screening the rhabdom in bright light and uncovering it in darkness or dim light. Migration of the distal pigment in the fiddler crab, Uca pugilalor, is regulated by a light-adapting hormone and a dark-adapting hormone. The black chromatophores of this crab are also controlled by a pair of hormones. Both pigmentary effectors exhibit circadian rhythms. The effects of some organic and inorganic pollutants on the ability of Uca pugilator to change color have been described. Exposure of this crab to naphthalene or cadmium results in decreased ability to disperse the pigment in their black chromatophores, the exposed crabs becoming paler than the unexposed crabs. Norepinephrine triggers release of both the black pigment-dispersing hormone and the light-adapting hormone. In view of the facts that (a) these hormones which regulate the black chromatophores and distal pigment are synthesized in and released from the eyestalk neuroendocrine complex, (b) the black pigment-dispersing hormone and the light-adapting hormone may actually be the same hormone. having two different activities and (c) release of both the black pigment-dispersing hormonemore » and the light-adapting hormone is triggered by norepinephrine, the present investigation was carried out to determine the effect of cadmium on distal pigment migration in Uca pugilator. More specifically, for comparison with the previously reported effect of cadmium on pigment migration in the black chromatophores, we wished to determine whether the distal pigment of fiddler crabs exposed to cadmium chloride is capable of as wide a range of movement as in unexposed crabs, and if not what might be the explanation. This is the first report of the effect of a pollutant on a retinal pigment of any crustacean. 12 refs., 3 tabs.« less