Uca Thayeri Research Articles

Uca (Petruca), a new subgenus for the rock fiddler crab Uca panamensis (Stimpson, 1859) from Central America, with comments on some species of the American broad-fronted subgenera.

Among the fiddler crabs from the Americas, Uca panamensis (Stimpson, 1859) (Crustacea: Decapoda: Ocypodidae) is unusual in its behavior and ecology, living in stony habitats rather than sandy or muddy substrates. This species also has several unusual morphological characters of the carapace and major and minor chelae, and had been placed in either the subgenera Minuca Bott, 1954, or Leptuca Bott, 1973. The armature at the inner corner of the orbital floor, as well as the morphology of the urocardiac ossicles of the gastric mill of U. panamensis, are, however, plesiomorphic characters, and are closer to the condition in species belonging the subgenera Uca and Afruca. Phylogenetic relationships, based on mitochondrial 16S rDNA and cytochrome oxidase subunit I, and nuclear 28S rDNA, supported by its unusual morphological features indicate that this species belongs to its own subgenus. A new subgenus Uca (Petruca) subgen. nov. is herein established for U. panamensis. In addition, the status of Uca thayeri Rathbun, 1900, U. umbratila Crane, 1941, U. virens Salmon & Atsaides, 1968, and U. longisignalis Salmon & Atsaides, 1968, are revised and discussed based on a reappraisal of their phylogenetic relationships.

Fiddler crabs (Uca thayeri, Brachyura: Ocypodidae) affect bacterial assemblages in mangrove forest sediments

To clarify the relationship between the detritivore fiddler crab, Uca thayeri, and sediment bacteria, we quantified morphotype richness, abundance and evenness of these microorganisms inside the crabs’ guts and in mangrove-associated sediments in Sisal, Mexico (21° 9′ N, 90° 1′ W) from July to September 2008. Increased bacterial richness and abundance were observed in mesocosm experiments when nutrients were added to the sediment or in the absence of fiddler crabs. Thus, crab disturbance seems to play a role in shaping the bacterial assemblage by reducing richness and abundance just as nutrient limitation does. Crabs can also play a second role by harboring a subset of bacterial morphotypes inside their gut. We exposed sterile sediment to fiddler crabs and found that viable cells were expelled from the crab’s gut and proliferated in previously sterile substratum. The bacterial community is thus structured by the foraging behavior of fiddler crabs since it benefits some bacteria and restricts others. By agar plating we have obtained conservative results, yet the data suggest that the crab influences the bacterial assemblage in two ways by allowing inoculation of the sand from the gut and reducing bacteria diversity through disturbance when foraging on sediments.

Sediment Particle Selection During Feeding by Four Species of UCA (Brachyura, Ocypodidae)

Differences in sorting of sediment grain-size during the feeding activity of fiddler crabs were investigated experimentally in four Uca species that have different numbers of spoon-tipped setae on the second maxillipeds. Uca leptodactylus had the highest number of spoon-tipped setae, followed by Uca rapax and Uca thayeri; whereas Uca vocator had no setae of this type. The crabs were allowed to feed for 48 h, in containers filled with three types of sediments with different particle-size composition. The feeding pellets formed in each type of sediment were collected, and the proportion of each granulometric fraction was compared with the substrate in the container. The diameters of the sediment particles found in the crab stomachs were measured and compared among the species and the types of sediments. The granulometry of the feeding pellets in each substrate was similar among the species. The size of particles ingested by fiddler crabs reflected the granulometric composition of the experimental substrate. Only U. leptodactylus ingested the smallest grains in coarser sediments. Therefore, the variation in the number of spoon-tipped setae on the second maxilliped seems not to affect the ability of fiddler crabs to manipulate and sort different particle sizes during feeding.

Is the Hatching Clock of Fiddler Crab Larvae (Uca thayeri) Phenotypically Plastic?

Larval release by adult fiddler crabs occurs during the ebbing tides, but its timing relative to the day-night and tidal amplitude cycles depends upon tidal form, e.g., shows phenotypical plasticity. Crabs (Uca thayeri) from Florida's East Coast are exposed to semidiurnal tides and release their larvae at night, whereas crabs from Florida's West Coast are exposed to mixed tides and release their larvae during the afternoon. The purpose of this study was to determine whether the larvae would hatch at other times, specifically those dictated by females from a different coast. To find out, clusters of eggs at similar stages of development, 24-72 h in advance of release, were reciprocally transferred between females from each location. Release of both the transferred and maternal larvae occurred synchronously, at the time dictated by the female's tidal regime. These results indicate that fiddler crab embryos can either advance or delay their hatching clock to match the temporal regime dictated by a brooding female.

Is the Hatching Clock of Fiddler Crab Larvae (Uca Thayeri) Phenotypically Plastic?

Larval release by adult fiddler crabs occurs during the ebbing tides, but its timing relative to the day-night and tidal amplitude cycles depends upon tidal form, e.g., shows phenotypical plasticity. Crabs (Uca thayeri) from Florida's East Coast are exposed to semidiurnal tides and release their larvae at night, whereas crabs from Florida's West Coast are exposed to mixed tides and release their larvae during the afternoon. The purpose of this study was to determine whether the larvae would hatch at other times, specifically those dictated by females from a different coast. To find out, clusters of eggs at similar stages of development, 24-72 h in advance of release, were reciprocally transferred between females from each location. Release of both the transferred and maternal larvae occurred synchronously, at the time dictated by the female's tidal regime. These results indicate that fiddler crab embryos can either advance or delay their hatching clock to match the temporal regime dictated by a brooding female.

Population and reproductive biology of the fiddler crab Uca thayeri Rathbun, 1900 (Crustacea: Ocypodidae) in a tropical mangrove from Northeast Brazil

Abstract Population and reproductive biology of Uca thayeri Rathbun, 1900 were studied for the first time in a tropical mangrove. Absolute density, sex ratio, population structure, handedness, breeding season and fecundity were investigated. Seven transects were delimited in a mangrove area of the Pacoti River, Northeast of Brazil (3° 43′ 02″ S/38° 32′ 35″ W). On each transect, ten 0.25 m2 squares were sampled on a monthly basis during low tide periods from September 2003 to August 2004. A total of 483 crabs were obtained, of which 250 were males, 219 non-ovigerous females, and 14 ovigerous females. The U. thayeri population presented bi-modal size frequency distribution, with males and non-ovigerous females not differing significantly size-wise. Ovigerous females were larger than males and non-ovigerous females. The overall sex ratio (1:1.07) did not differ significantly from the expected 1:1 proportion. The major cheliped was the right one in 50% of the males. The observed density was of 8.5 individuals/m2, with the specimens being found mostly in shaded areas. Ovigerous females were found in 5 months of the year, coinciding with the rainy season, suggesting that the population of U. thayeri presents seasonal reproductive events. Juvenile crabs were more abundant during the dry period, while larger crabs were found mainly during the rainy period. The fecundity of the studied population was much smaller than that of subtropical populations of this species. The regression analysis shows that the number of eggs increases linearly with the increase of carapace width.

Distribuição e abundância dos caranguejos Uca Leach (Crustacea, Decapoda, Ocypodidae) na Baía de Guaratuba, Paraná, Brasil

Um estudo sobre distribuição espacial e abundância dos chama-marés Uca Leach, 1814 foi realizado na Baía de Guaratuba, Estado do Paraná. Foram coletados chama-marés de dez biótopos ao longo de um gradiente de salinidade de zero a 32 dentro da Baía de Guaratuba. Foram obtidas sete espécies, entre as quais, Uca mordax (Smith, 1870) que foi registrada somente em biótopos inundados por águas de baixas salinidades (de zero a 16). As demais espécies mostraram tolerância a uma ampla variação de salinidade, mas Uca maracoani (Latreille, 1802-1803) e Uca leptodactyla Rathbun, 1898 predominaram em águas mais salinas, de 14 a 32, enquanto U. burgersi Holthuis, 1967, Uca rapax (Smith, 1870), Uca thayeri Rathbun, 1900 e Uca uruguayensis Nobili, 1901 foram coletadas em mais de três biótopos e mostraram uma tendência ao eurihalismo, suportando salinidades de 4 a 32. Entretanto, outras características do substrato tais como porcentagem relativa de cascalho/areia/silte/argila, teor de matéria orgânica e presença de marismas, também, influenciaram a distribuição espacial destes caranguejos. U. leptodactyla foi registrada com densidade máxima de 240 ind.m-2, o mais alto valor conhecido.

Reproductive pattern comparison of Uca thayeri Rathbun, 1900 and U. uruguayensis Nobili, 1901 (Crustacea, Decapoda, Ocypodidae)

Ovigerous females of Uca thayeri and U. uruguayensis were used to achieve and compare their reproductive pattern. The females mean size was 6.6 ± 0.8mm for U. uruguayensis and 17.3± 4.4mm for U. thayeri. The mean fecundity obtained for U. uruguayensis was 1883 ± 490 eggs (N = 27) and for U. thayeri was 31068 ± 11186 eggs (N = 31). The differences observed in reproductive pattern of U. thayeri and U. uruguayensis suggest an adaptive strategy by each species: U. thayeri presented seasonal reproduction with a pronounced intensity from January to March and higher fecundity, while U. uruguayensis reproduction was continuous all year round, but with lower fecundity.

Evidence for a two pigment visual system in the fiddler crab, Uca thayeri.

Intraocular recordings were made from the eyestalks of dark-adapted fiddler crabs (Uca thayeri) during presentation of monochromatic light flashes of different wavelengths and intensities. Two types of signals were recorded in different experiments: slow potentials (electroretinogram) and fast potentials (spikes). The latter were also recorded in the presence of a continuous green or red adapting light. The resulting visual spectral-sensitivity curves, when fitted to rhodopsin-based visual pigment absorption spectra (from Dartnall nomograms), indicated the presence of two visual pigments, one with an absorption maximum near 430 nm, and the other with a peak absorption between 500 nm and 540 nm. The data also provided evidence for some differential bleaching of the pigments in the presence of a colored adapting light, but most of the adaptation effect was probably due to changes in screening pigment and neural desensitization or inhibition. These two observations suggest that an adequate substrate for color vision may exist in this and other species of fiddler crabs. The electroretinogram and spike-recording methods produced similar visual-sensitivity data, suggesting that latter technique, a much more efficient way of collecting data that is physiologically relevant, may be the method of choice for determining spectral sensitivity in crustaceans.

HATCHING RHYTHMS OF UCA THAYERI: EVIDENCE FOR PHENOTYPIC PLASTICITY

Abstract Fiddler crabs (Uca thayeri) on Florida's east and west coasts show temporally distinct hatching rhythms, correlated with differences in tidal form. Our purpose in this study was to determine whether these differences were fixed or could change in response to variation in the tides. West coast crabs (but not east coast crabs) showed seasonal variation in their hatching rhythms correlated with seasonal variation in the tides. In the spring, they released larvae at night. In the summer, hatching occurred during the day. West coast crabs transferred to Florida's east coast within four weeks released larvae at night in a rhythm similar to resident crabs but different from the spring nocturnal rhythm shown at their home beach. We conclude that this species has a flexible hatching rhythm that changes under natural, as well as under experimental, conditions. Such flexibility may permit the crabs to time larval release optimally over a range of tidal forms. This study and others published recently suggest...

How important are mangroves as a carbon source for decapod crustacean larvae in a tropical estuary?

In order to evaluate the importance of mangrove leaf detritus as a food source for deca- pod crustacean larvae, stable isotopes (δ 13 C and δ 15 N) were measured in the tissue of these larvae and other selected organisms. Decapod crustacean larvae and planktonic adult decapods, Lucifer faxoni and Acetes americanus, were sampled in the Itamaraca estuarine system, Brazil. For comparison with stable isotope values in the estuary, plankton and POM samples were also taken on the adjacent con- tinental shelf. In the Itamaraca estuarine system, δ 13 C of decapod larvae and the holoplanktonic decapods L. faxoni and A. americanus ranged from about -17 to -23‰ (mean: -19.8 ± 1.5‰). This indicates that the contribution of mangrove carbon (δ 13 C: -26.8‰) to larval nutrition was generally negligible. Among decapod larvae, porcellanid zoeae showed relatively low δ 13 C values, while penaeid shrimp postlarvae showed the highest δ 13 C. Porcellanid zoeae were thus the only decapod larvae with a considerable percentage (13 to 40%) of mangrove carbon in their tissue. However, these low values may also be due to a negative isotope shift that occurs during embryogenesis. Feed- ing experiments with zoeae of Petrolisthes armatus (Anomura: Porcellanidae) and Sesarma rectum (Brachyura: Grapsidae) showed assimilatory shifts of up to 1.0 ± 0.2‰ for 13 C and up to 1.4 ± 0.6‰ for 15 N. Analysis of embryonic isotope fractionation for 5 decapod crustacean species, P. armatus, S. rectum, Aratus pisonii, Uca thayeri, and U. maracoani, showed that larval tissue was 13 C-depleted by up to 3.8‰ and 15 N-depleted by up to 2.3‰ in relation to parental tissue.

Hatching Rhythms of Uca Thayeri: Evidence for Phenotypic Plasticity

Hatching Rhythms of Uca Thayeri: Evidence for Phenotypic Plasticity

Hatching rhythms of Uca thayeri Rathbun: timing in semidiurnal and mixed tidal regimes.

We compared the timing of larval release by Uca thayeri exposed to different tidal regimes. Crabs on Florida's East Coast experience semidiurnal tides, whereas crabs on the Florida's West Coast experience mixed tides.In both populations, hatching occurred shortly after high tide. On the East Coast, most crabs released their larvae between dusk and midnight, a few days before the maximum amplitude spring tides. On the West Coast, most crabs released their larvae during the afternoon tropic tides of greater amplitude. West Coast crabs may release during the day because ebbing tides at night are too weak for effective transport. Thus, at each location, hatching occurs when phase relationships between the ebbing tides, the light-dark cycle, and tidal amplitude are most favorable. Further study is required to determine whether females on each Coast show fixed responses to each tidal regime, or whether they can alter their hatching rhythms upon exposure to different tides.

On the Reproductive Behavior of the Fiddler Crab Uca thayeri, with Comparisons to U. pugilator and U. vocans: Evidence for Behavioral Convergence

On the Reproductive Behavior of the Fiddler Crab Uca thayeri, with Comparisons to U. pugilator and U. vocans: Evidence for Behavioral Convergence

ON THE REPRODUCTIVE BEHAVIOR OF THE FIDDLER CRAB UCA THAYERI, WITH COMPARISONS TO U. PUGILATOR AND U. VOCANS: EVIDENCE FOR BEHAVIORAL CONVERGENCE

ABSTRACT The fiddler crabs have been separated into two major species groups: the fronts (with wide spaces between their eyestalks) of the New World, which may show resourcebased mating systems, and the fronts of the Indo-Pacific, which may show resource-free mating systems. A few species, however, are known to deviate both structurally and behaviorally from these patterns. One (Uca thayeri) was studied to determine why. My data show that U. thayeri has a resource-free mating system, behaves much like a narrow front, but possesses the reproductive physiology of a broad front. Studies by others indicate it is closely related to the broad fronts, yet shows many ecological similarities to the narrow fronts. The evidence suggests, then, that the reproductive behavior of U. thayeri is best explained by evolutionary convergence. This result constitutes further evidence that differences between the two groups are best viewed as alternative adaptations.