Showing papers on "Uca pugilator published in 2007"

Costs of bearing a sexually selected ornamental weapon in a fiddler crab

Abstract: Summary 1Sexually selected structures with dual function of combat and display are likely to be honest signals of male quality to opponents and mates, but should be costly to produce and maintain. 2Male fiddler crabs use a single greatly enlarged claw as both a weapon in agonistic contests with other males and an ornament to attract females for mating. Given the extreme size of this structure (up to half the total body mass), there is surprisingly little evidence for costs as predicted by theory. 3We experimentally investigated several potential costs of the large claw to male sand fiddler crabs Uca pugilator. Mass-specific metabolic rates were significantly higher and treadmill endurance capacity significantly lower for males bearing an intact major claw compared with those without. 4In contrast, presence of the claw did not affect maximal sprint speeds, suggesting that the massive structure does not compromise the ability of male crabs to evade predators. These counterintuitive results conform to recent theoretical models of energy costs of locomotion. 5Our study provides empirical support for a key assumption of sexual selection theory – energetic and endurance-related locomotor costs incurred while bearing this ornamental weapon act in opposition to sexual selection favouring larger claws.

Spectral sensitivity of four species of fiddler crabs (Uca pugnax, Uca pugilator, Uca vomeris and Uca tangeri) measured by in situ microspectrophotometry.

Abstract: SUMMARY Fiddler crabs have compound eyes that are structurally fairly well understood. However, there has been much debate regarding their spectral sensitivity and capacity to enable colour discrimination. We examined the visual pigments of two North-American species ( Uca pugnax and U. pugilator ), one species from the Indo-West Pacific ( U. vomeris ) and the only Eastern-Atlantic species ( U. tangeri ) of fiddler crabs using in situ microspectrophotometry of frozen sections of dark-adapted eyes. Only one spectral class of visual receptor was found in the larger (R1–7) retinular cells of each species, with maximum absorption peaking between 508 nm and 530 nm (depending upon species). The R8 retinular cell, that might contain a short-wavelength sensitive photopigment and provide a basis for colour vision, was too small to analyze by these methods. Rhabdoms were lined with screening pigment which strongly influenced each species9 spectral sensitivity, sharpening the peak and shifting the maximum towards longer wavelengths, on occasion to as far as the 600 nm region. We hypothesize that sensitivity to longer wavelengths enhances contrast between background (blue sky or tall vegetation) and the male major claw during the waving display.

Circatidal swimming behavior of brachyuran crab zoea larvae: implications for ebb-tide transport

Abstract: Larvae of the blue crab Callinectes sapidus and fiddler crab Uca pugilator are exported from estuaries and develop on the continental shelf. Previous studies have shown that the zoea-1 larvae of some crab species use selective tidal-stream transport (STST) to migrate from estuaries to coastal areas. The STST behavior of newly hatched larvae is characterized by upward vertical migration during ebb tide followed by a descent toward the bottom during flood. The objectives of the study were (1) to determine if newly hatched zoeae of U. pugilator and C. sapidus possess endogenous tidal rhythms in vertical migration that could underlie STST, (2) to determine if the rhythms persist in the absence of estuarine chemical cues, and (3) to characterize the photoresponses of zoeae to assess the impact of light on swimming behavior and vertical distribution. Ovigerous crabs with late-stage embryos were collected from June to August 2002 and maintained under constant laboratory conditions. Following hatching, swimming activity of zoeae was monitored in darkness for 72 h. U. pugilator zoeae displayed a circatidal rhythm in swimming with peaks in activity occurring near the expected times of ebb currents in the field. Conversely, C. sapidus zoeae exhibited no clear rhythmic migration patterns. When placed in a light field that simulated the underwater angular light distribution, C. sapidus larvae displayed a weak positive phototaxis at the highest light levels tested, while U. pugilator zoeae were unresponsive. Swimming behaviors and photoresponses of both species were not significantly influenced by the presence of chemical cues associated with offshore or estuarine water. These results are consistent with predictions based on species-specific differences in spawning and the proximity of hatching areas to the mouths of estuaries. U. pugilator larvae are released within estuaries near the adult habitat. Thus, ebb-phased STST behavior by zoeae is adaptive since it enhances export. Selective pressures for a tidal migration in C. sapidus larvae are likely weaker than for U. pugilator since ovigerous females migrate seaward prior to spawning and hatching occurs near inlets and in coastal waters.

Circatidal swimming behaviors of fiddler crab Uca pugilator larvae from different tidal regimes

Abstract: Fiddler crab Uca pugilator larvae are released within estuaries near the time of high tide and are exported offshore to undergo development. Previous studies indicate that zoea-1 larvae use selective tidal-stream transport (STST) to migrate from adult habitats to shelf waters. In areas with semidiurnal tides, this behavior is mediated by a circatidal rhythm that is characterized by upward swimming toward the surface during ebb tide, followed by a descent toward the bottom during flood tide. We tested the hypothesis that U. pugilator zoeae from different tidal regimes possess activity rhythms that match local tidal patterns. Ovigerous crabs with late-stage embryos were collected from areas with semidiurnal, diurnal, and mixed tides and from an area within a microtidal coastal lagoon. Following hatching, swimming activity was monitored under constant conditions for 96 h. Zoeae from semidiurnal and diurnal regimes possessed activity rhythms with free-running periods that matched the tides at the collection sites (≈12.4 and 24.8 h, respectively). Crabs from beaches with mixed tides displayed asymmetrical oscillations in swimming activity with dominant periodicities that corre- sponded to the semidiurnal and diurnal constituents of the tides. Zoeae from microtidal areas pos- sessed rhythms that were similar to those observed in crabs from areas with semidiurnal tides. At all locations, peaks in activity occurred during the time of expected ebb currents, which is consistent with STST behavior favoring seaward transport. Differences in larval activity patterns suggest that STST behaviors are controlled by separate circatidal and circalunidian clocks or paired circalunidian clocks coupled in antiphase.

Differences in Body Size and Water Balance Strategies between North Carolina and Florida Populations of the Sand Fiddler Crab, Uca Pugilator

Abstract: Sand fiddler crabs, Uca pugilator, from North Carolina (NC) are two-times smaller than ones from Florida (FL). A water balance study was conducted to examine this size difference in relation to possible changes in habitat suitability. Like most crabs, U. pugilator are classified as hydrophilic, which is consistent with their preference for humid environments. In contrast to the North Carolina population, U. pugilator-FL loses water less rapidly and has higher percentage body water content, a water balance strategy that emphasizes retention. Conversely, the amount of body water required is less for U. pugilator-NC, enabling it to maintain water balance despite having a higher water loss rate. Both tolerated only about 1/4 loss of body water before succumbing to desiccation. Neither experienced a critical transition temperature, CTT. We concluded that water balance profiles of these two populations are complementary, representing trade-offs that permit survival in a moisture-rich habitat. Lower bod...

Carolina and florida populations of the sand fiddler crab, uca pugilator

Abstract: Sand fiddler crabs, Uca pugilator, from North Carolina (NC) are two-times smaller than ones from Florida (FL). A water balance study was conducted to examine this size difference in relation to possible changes in habitat suitability. Like most crabs, U. pugilator are classified as hydrophilic, which is consistent with their preference for humid environments. In contrast to the North Carolina population, U. pugilator-FL loses water less rapidly and has higher percentage body water content, a water balance strategy that emphasizes retention. Conversely, the amount of body water required is less for U. pugilator-NC, enabling it to maintain water balance despite having a higher water loss rate. Both tolerated only about 1/4 loss of body water before succumbing to desiccation. Neither experienced a critical transition temperature, CTT. We concluded that water balance profiles of these two populations are complementary, representing trade-offs that permit survival in a moisture-rich habitat. Lower body water content, however, overlaps with features of arthropods that thrive at low temperature, suggesting that U. pugilator-NC may be more cold tolerant.