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Path integration is the navigational process by which animals construct a memory of a previous location by continuously measuring and summing their movements to form a single home vector pointing to the starting location. It is intrinsically error prone, subject to random errors and, potentially, to systematic errors in either measurement or the summing algorithm. Both types of errors lead to an incorrect vector memory and thus to an error in homing. Because the errors are incurred when animals move, they are theoretically predictable from the movements. We analyzed the behavior of fiddler crabs (Leptuca pugilator) as they performed foraging excursions followed by homing with varying degrees of error. From video recordings we measured body orientations and locations and computed these spatiotemporal path characteristics: duration, distance, turns, bearing and arc sector. These were analyzed for their effect on, separately, the magnitude, and the direction, of crabs' homing error. The magnitude of the homing error was predicted by arc sector, Dbearing and path length, and several interactions. The direction of the homing error was predicted by interactions including arc sector x Dbearing, arc sector x turns, and Dbearing x turns. Covariance among these factors results in a path that traces a large arc while maintaining body orientation toward the burrow direction and leads to an error with the same clockwise/counterclockwise sign as the arc and the body turns. These results place L. pugilator's path integration mechanism among others with known systematic errors. [ABSTRACT FROM AUTHOR]

Path integration is the navigational process by which animals construct a memory of a previous location by continuously measuring and summing their movements to form a single home vector pointing to the starting location. It is intrinsically error prone, subject to random errors and, potentially, to systematic errors in either measurement or the summing algorithm. Both types of errors lead to an incorrect vector memory and thus to an error in homing. Because the errors are incurred when animals move, they are theoretically predictable from the movements. We analyzed the behavior of fiddler crabs (Leptuca pugilator) as they performed foraging excursions followed by homing with varying degrees of error. From video recordings we measured body orientations and locations and computed these spatiotemporal path characteristics: duration, distance, turns, bearing and arc sector. These were analyzed for their effect on, separately, the magnitude, and the direction, of crabs’ homing error. The magnitude of the homing error was predicted by arc sector, Δbearing and path length, and several interactions. The direction of the homing error was predicted by interactions including arc sector x Δbearing, arc sector x turns, and Δbearing x turns. Covariance among these factors results in a path that traces a large arc while maintaining body orientation toward the burrow direction and leads to an error with the same clockwise/counterclockwise sign as the arc and the body turns. These results place L. pugilator’s path integration mechanism among others with known systematic errors.

As animals execute essential behaviors like foraging, they must orient with respect to the space around them, requiring some neural/behavioral mechanism for spatial navigation. One such navigation mechanism is path integration, whereby animals recall their starting point by creating a memory-stored home vector. In some animals, this is stored in an egocentric frame of reference; however, it remains unclear what comprises this in animals' spatial memory. The fiddler crab Uca pugilator makes an excellent model to investigate the nature of the egocentric frame of reference because they appear to path integrate using self-motion cues to form an egocentric vector. We hypothesized that the home vector direction is governed by the optokinetic system, since the eye–body angle explicitly reflects the deviation of the body axis from home direction as optokinetic eye movements stabilize the eyes against body rotation. To test this hypothesis, we monitored eye and body movements during foraging excursions of crabs showing varying degrees of visual stabilization. We found that crabs with good eye stability had more accurate home vectors than those with poor eye stability, and the quantitative degree of stability accurately predicted the crabs' perception of home direction. These results suggest that eye movement reflexes may establish the homing direction in path integrating fiddler crabs. [ABSTRACT FROM AUTHOR]

In biologically diverse ecosystems, an essential process to support competing species to coexist is ecological differentiation. Habitat heterogeneity is, hence, important in establishing species abundance and richness, favoring the coexistence of species due to habitat partition. In this context, shading and species thermal tolerance can be good factors to elucidate the role of habitat heterogeneity in the habitat partition among closely related species. Herein, we study shading effects in microhabitat selection, behavior, and physiological limitation on two species of fiddler crabs (Leptuca leptodactyla and Leptuca uruguayensis). Indeed, shading conditions influenced fiddler crabs species proportion over time, with L. leptodactyla more associated with nonshaded/warmer areas while the L. uruguayensis to shaded/cooler ones. They also adjusted their behavior differently from each other to deal with thermal stress. Finally, we have demonstrated that these effects are related to species' physiological limitations. We conclude that biologically diverse ecosystems, such as intertidal regions from estuaries (e.g., mudflats and mangroves), support the coexistence between closely related species by reducing competition due to habitat partition. [ABSTRACT FROM AUTHOR]

Saltmarshes are important global carbon (C) sinks, but the considerable uncertainty in the C budget and the underlying mechanisms limit the estimation of greenhouse gas emissions (GHG, e.g., CO2 and CH4) in the context of global climate change. To ascertain the mechanistic understanding, we assessed how crab burrows morphology and greenhouse gas effluxes changed in response to interactions of fiddler crab burrow density, soil organic matter content (high vs low), and presence/absence of Spartina alterniflora (vegetated saltmarsh vs nearby unvegetated mudflat) on the coast of New England (USA). The crab burrow volume in the vegetated saltmarsh was smaller than that in the mudflat, and crab burrow volume greatly correlated with soil CO2 efflux, indicating that crab activities could enhance coastal wetland CO2 efflux. Soil CO2 and CH4 effluxes rates were significantly positively correlated with crab burrow density, organic matter content, and vegetation types. Specifically, the higher soil organic matter content and crab burrow density greatly increased soil heterotrophic respiration in the saltmarsh. Overall, with crab disturbances, soil CO2 and CH4 efflux increased by 32.1% and 47.9%, respectively. This study highlights that fiddler crab burrowing activity plays an important role in the C sequestration of coastal blue C ecosystems (BCEs).

As animals execute essential behaviors like foraging, they must orient with respect to the space around them, requiring some neural/behavioral mechanism for spatial navigation. One such navigation mechanism is path integration, whereby animals recall their starting point by creating a memory-stored home vector. In some animals, this is stored in an egocentric frame of reference; however, it remains unclear what comprises this in animals’ spatial memory. The fiddler crab Uca pugilator makes an excellent model to investigate the nature of the egocentric frame of reference because they appear to path integrate using self-motion cues to form an egocentric vector. We hypothesized that the home vector direction is governed by the optokinetic system, since the eye–body angle explicitly reflects the deviation of the body axis from home direction as optokinetic eye movements stabilize the eyes against body rotation. To test this hypothesis, we monitored eye and body movements during foraging excursions of crabs showing varying degrees of visual stabilization. We found that crabs with good eye stability had more accurate home vectors than those with poor eye stability, and the quantitative degree of stability accurately predicted the crabs’ perception of home direction. These results suggest that eye movement reflexes may establish the homing direction in path integrating fiddler crabs.

This study aimed to investigate the population biology of Minuca mordax in the Igaraçu River, Parnaíba, analyzing frequency distribution in size classes, reproductive period, relative growth, morphological sexual maturity, sex ratio and heterochely. The crabs were manually collected, randomly, by two people for 1 hour, in the representative months of the dry season (September to November) and rainy (April to June). In laboratory the crabs were identified, separated according to sex and measured. A total of 610 samples were captured, with 453 males and 157 females. The average size of carapace width (CW) was significantly different (p < 0.05) between males (17.21 ± 3.68 mm) and females (15.06 ± 3.18 mm). The distribution of the crabs in size classes was unimodal for both sexes. The morphological sexual maturity obtained for males was 12.42 mm CW and females was 10.05 mm CW. The sex ratio for the population was 1:0.35 (male: female), with significant difference from the expected ratio of 1:1. The heterochely was observed only in males of the species (224 right-handed and 229 sinister). Subsequently, other on-site observations were carried out monthly, from February/2011 to January/2012 to observe ovigerous females and determine the reproductive period. Females with eggs were observed only from March to June, corresponding to the rainy season in the region. The results found in the present study are similar to those observed in other populations of violinist crabs and suggest that the population is stable in the environment. The present study provides subsidies for the conservation of the species in the Igaraçu River.

Salt marshes are globally important sites of carbon burial, but microbial processes in their soil produce potent greenhouse gases such as carbon dioxide (CO2) and methane (CH4) that can be released back to the atmosphere. Although a great deal is known about how shifting seasons, tides, and salinity influence salt marsh greenhouse gas emissions, little effort has been devoted to understanding how emissions respond to bioturbation and pollution. In this study, we evaluated how fiddler crab bioturbation and oil pollution altered CO2 and CH4 fluxes from Louisiana salt marsh soil through a series of microcosm incubation experiments. CO2 and CH4 fluxes did not consistently increase as a function of crab burrow depth even though soil CO2 and CH4 concentrations increased with depth. Instead, regardless of burrow depth, CO2 and CH4 fluxes were highest (536.7 ± 41.6 and 6.35 ± 0.59 nmol g−1 h−1, respectively) immediately after burrowing activity ceased and within ~ 2 h decreased to a low background level (117.4 ± 17.1 and 0.53 ± 0.26). These background CO2 fluxes persisted through the end of our experiments, but background CH4 fluxes were not detectable after < 1 day, suggesting an important role for methanotrophy. Therefore, crab burrow size had a strong influence on CO2 fluxes, while the rate of burrow excavation was more important for CH4 fluxes. Low to moderate oil concentrations (up to 25.55 mg cm−2) did not alter greenhouse gas fluxes. However, severe oil contamination that decreases fiddler crab abundance and burrowing activity will also indirectly decrease salt marsh greenhouse gas emissions. These findings illuminate the importance of fiddler crab bioturbation to salt marsh carbon cycling and export. [ABSTRACT FROM AUTHOR]

Human recreational visits to tidal flats increase trampling pressure, which has a significant impact on the coastal benthic ecosystem. The fiddler crab Austruca lactea, which inhabits the upper intertidal region, is endangered in temperate regions such as Japan and South Korea. The vulnerability of their habitat to human activities along with their limited summer reproduction period may have contributed to the decrease in fiddler crab populations in these regions. We conducted experiments to elucidate the effects of trampling on the surface activities and courtship behaviors of A. lactea, which represent ecological indicators for tidal flat ecosystems. During the 46-day trampling period, we observed the number of active crabs on the surface of the tidal flat under three different trampling intensities (heavy trampling = 60 steps/m2; moderate trampling = 20 steps/m2; and no trampling). The density of individuals of both sexes active on the surface and that of courting males significantly decreased under both heavy and moderate trampling intensities. In addition, the feeding and courtship rhythms of male A. lactea collapsed under continuous trampling events. We monitored the site once per week, and surface activity did not recover fully until the sixth week after the trampling period. Our results demonstrated that trampling on the tidal flat disrupted the intensity and timing of crab surface behavior and male reproductive surface behavior, and thus may, ultimately, have an impact on the population dynamics of A. lactea.

Synchrony can be defined as the precise coordination between independent individuals, and this behaviour is more enigmatic when it is imperfect. The traditional theoretical explanation for imperfect synchronous courtship is that it arises as a by-product of the competition between males to broadcast leading signals to attract female attention. This competition is considered an evolutionary stable strategy maintained through sexual selection. However, previous studies have revealed that leading signals are not honest indicators of male quality. We studied imperfect courtship synchrony in fiddler crabs to mainly test whether (i) signal leadership and rate are defined by male quality and (ii) signal leadership generates synchrony. Fiddler crab males wave their enlarged claws during courtship, and females prefer leading males—displaying ahead of their neighbour(s). We filmed groups of waving males in the field to detect how often individuals were leaders and if they engaged in synchrony. Overall, we found that courtship effort is not directly related to male size, a general proxy for quality. Contrary to the long-standing assumption, we also revealed that leadership is not directly related to group synchrony, but faster wave rate correlates with both leadership and synchrony. This article is part of the theme issue 'Synchrony and rhythm interaction: from the brain to behavioural ecology'. [ABSTRACT FROM AUTHOR]

Abstract Bergmann's rule predicts that organisms at higher latitudes are larger than ones at lower latitudes. Here, we examine the body size pattern of the Atlantic marsh fiddler crab, Minuca pugnax (formerly Uca pugnax), from salt marshes on the east coast of the United States across 12 degrees of latitude. We found that M. pugnax followed Bergmann's rule and that, on average, crab carapace width increased by 0.5 mm per degree of latitude. Minuca pugnax body size also followed the temperature–size rule with body size inversely related to mean water temperature. Because an organism's size influences its impact on an ecosystem, and M. pugnax is an ecosystem engineer that affects marsh functioning, the larger crabs at higher latitudes may have greater per‐capita impacts on salt marshes than the smaller crabs at lower latitudes.

In southern Puerto Rico along the coastline bordering the Jobos Bay National Estuarine Research Reserve, environmental encroachment has exposed mangrove forest to different sources of pollution. Potentially toxic element concentrations from the F1Tess (exchangeable), F4Tess (oxidizable), mangrove leaf litter (MLL), and fiddler crab whole body soft tissue were analyzed to assess the fate and transport of pollutants from the environment and its transition into flora-fauna via trophic transfer. Geo-accumulation factor values suggest the bay has experienced limited to no pollution when combining the concentrations of potentially toxic elements extracted from the F1Tess and F4Tess sediment fractions. These geochemical sedimentary compartments are considered “bioavailable” to flora-fauna as evidenced by the bioaccumulated Cd-Ba-V-Cu-Zn-As-Se in the leaf litter of the black mangrove Avicennia germinans and in the fiddler crab Uca rapax. The biota-sediment accumulation factor (F1Tess + F4Tess) demonstrated that Uca rapax behave like a de-concentrator for most pollutants and as a macro-concentrator for Cu-As, while the bioconcentration factors identified only Cu-As-Se as being actively bioaccumulated in the fiddler crabs. Of all the potentially toxic elements studied, As is the only one to be biomagnified via sediment-Avicennia germinans leaf litter-Uca rapax food chain. An unexpected find of this study was that the excavated sediment “pellets” by Uca rapax contained up to 4x the concentrations of Cd-Ba-V-Cr-Co-Ni-Cu-Zn-As-Se when compared to the F1Tess sediment fraction from the surface, thus suggesting a variable redox boundary within the fiddler crab’s burrow.

The purpose of this development study is to develop research-based booklet for the identification of fiddler crab (Uca spp.) diversity. Some people do not yet know the ecological benefits of fiddler crabs. This is apparent when some people take fiddler crabs to serve as decorative crabs. The product specifications expected in the development of this medium are booklets. Therefore, it takes a companion learning media that can lead the local community to implement self-learning in the form of booklet because their interest of reading is very less, especially when reading a book that is colorless and has a lot of words. Booklet that is packed with interesting and accompanied by pictures is an alternative solution. The development method used in the research is Exploration, Explanation, and Evaluate (3E) model. The research was conducted by developing the research result into a booklet based on the diversity of fiddler crabs in mangrove ecosystem. The booklet validation consists of two lecturers from the Department of Biology Education at the University of Muhammadiyah Malang which is a material expert and learning media expert. The result of this research is booklet very valid with the percentage of material expert validity 81.25% and learning media expert 95.13%.

Uca crassipes (Adams and White 1848) is one of two species of fiddler crabs found on Mo’orea, French Polynesia. Much like other animal populations, U. crassipes is subject to density dependent processes, such as competition, which increase with density. To better understand the relationship between competition and density, this study first looked at habitat differences between 8 distinct populations of U. crasspies on Mo’orea. It then explored differences in aggressive interactions between crabs at one high-density and one low-density site. In the field, both male and female fiddler crabs were found to fight more in the high-density population. Subsequent investigation of the effect of density on aggression in laboratory settings did not yield significant results. Though laboratory results were not significant, trends in data showed more fighting under high-density conditions. Further investigation is necessary to fully understand the effects of density dependent processes on fiddler crabs in both a field and laboratory setting.

Research has been done in Ketapang mangrove area of Probolinggo city in months of September-November 2015. The objectives are to observe the fiddler crab community stucture and to analyze the effects of fiddler crabs on C/N ratio and redox potential of soil in mangrove ecosystems. The samples of fiddler crabs were taken during the low tides at 4 station (20 transects with sizes of 1 m2). Data of the fiddler crabs were measured from the soil digging insides the transect. The soil samples were taken from these crab holes wall (at the surface and at the depth of 20 cm), under the holes at the depth of 40 cm as well as from the locations that undwells by these animals at the same depth. The fiddler crab identified are U. Triangularis between 2 – 6 ind/m2, U paradussumieri 1 – 3 ind/m2, U perplexa 14 – 32 ind/m2, U dussumieri 12 – 27 ind/m2 and U. Tetragonon 3 – 6 ind/m2. The diversity is moderate (H = 1.7) and the dominance index was low (C = 0.37). C/N ratio soil were inhabited by fiddler crab between 6 – 14, the undwelled area were 14 – 20. Soil C/N ratio was inhabited by the fiddler crab at the surface and depth of 20 cm in average of 9 cm while at 40 cm in avergae of 12. The low of C/N ratio at surface and depth of 20 cm causing the organic matter turnover faster because the high nitorgen content. Soil potential redox (Eh) the undwelled areas was found –0.647 mV, meanwhile the soil Eh in the dwelled areas was positive (0.68 till 0.87 mV). This mean, the decpmposition was occured during aerobic condition and will produce untoxic subtances.

Bergmann's rule predicts that organisms at higher latitudes are larger than ones at lower latitudes. Here, we examine the body size pattern of the Atlantic marsh fiddler crab, Minucapugnax (formerly Uca pugnax), from salt marshes on the east coast of the United States across 12 degrees of latitude. We found that M. pugnax followed Bergmann's rule and that, on average, crab carapace width increased by 0.5 mm per degree of latitude. Minuca pugnax body size also followed the temperature–size rule with body size inversely related to mean water temperature. Because an organism's size influences its impact on an ecosystem, and M. pugnax is an ecosystem engineer that affects marsh functioning, the larger crabs at higher latitudes may have greater per‐capita impacts on salt marshes than the smaller crabs at lower latitudes. [ABSTRACT FROM AUTHOR]

Morphometric analysis of Austruca iranica population from the two different sites of Sandspit (Karachi, Pakistan) mangrove area was examined. Total seven growth related traits: carapace length (CL), carapace width (CW), enlarged chela length (En.Ch.L), enlarged chela width (En.Ch.W), abdominal length (Ab.L), abdominal width (Ab.W) and pleopod length (Pl.L= in male) examined for the relative growth analysis. Carapace width (CW) used as independentt variable to observe relationship between all the stated growth related traits. A total of 1,244 crabs were collected from both sites; among them 566 males and 628 females. Descript analysis showed (CW) ranged from (male = 3.5 mm to 18 mm) and (female = 2.5 mm to 16 mm) from station 1 and (male = 4.00 mm to 18.5 mm) and (female = 3.5 mm to 18 mm) from station 2. The overall sex ratio (p < 0.05) skewed in favor of females (0.91: 1.0) during South West Monsoon (SWM) season. Relationship between carapace length and carapace width showed positive allometric relation (R²=92.1%) in males. The females showed positive allometric relationship from carapace length and abdominal width (R²= 89.6 %). Overall significant difference observed in both males and females through size at sexual maturity from both sites. The logistic equation indicated that individuals reach at sexual maturity when they attain (male: CW50=6.65mm; female: CW50=6.20mm) from station 1 and (male: CW50=8.20mm; female: CW50=6.30mm) from station 2. [ABSTRACT FROM AUTHOR]

The aggregation of courting males is widespread among animal taxa, yet we do not understand why males congregate and therefore intensify local competition for female attention. The most commonly invoked theoretical explanation is that females preferentially approach clustered males due to the many benefits they would gain, and clustered males would therefore have higher mating success. However, although theoretical explanations of aggregation formation are well advanced, empirical studies are scarce, especially in invertebrates. In fact, there is little evidence that females do prefer to approach clustered displayers over spaced displayers. Here we address this question by using robotic crabs to test female preferences in fiddler crabs (a visually displaying species) and show that females do not preferentially approach clustered males. We suggest that if this pattern is more widespread, the most commonly invoked explanation of courting aggregations is of limited use. We offer explanations for the strong clustering behavior we observe in this species and discuss the implications of this finding for the theoretical underpinnings of this research field. [ABSTRACT FROM AUTHOR]

Territorial contests often occur in the presence of conspecifics not directly involved in the interaction. Actors may alter their behavior in the presence of this audience, an "audience effect," and audiences themselves may alter their behavior as a result of observing an interaction, a "bystander effect." Previous work has documented these effects by looking at each in isolation, but to our knowledge, none has investigated their interaction; something that is more likely to represent a realistic scenario for species where individuals aggregate spatially. We therefore have a somewhat limited understanding of the extent and direction of these potentially complex indirect social effects on behavior. Here, we examined how audience and bystander effects work in tandem to modify resident male aggressive behavior towards intruders in European fiddler crabs, Afruca tangeri. We found that male crabs with an audience showed greater aggressive behavior towards an intruder compared with males without an audience, but only if they had acted as a bystander to an aggressive signaling interaction prior to the intrusion. Indeed, bystanding during aggressive interactions elevated aggressive responses to intruders maximally if there was an audience present. Our results suggest that bystanding had a priming effect on territory-holding males, potentially by providing information on the immediate level of competition in the local neighborhood, and that same-sex audiences only matter if males have been primed. This study highlights the fundamental importance of considering broader interaction networks in studying real-world dyadic interactions and of including nonvertebrate taxonomic groups in these studies. [ABSTRACT FROM AUTHOR]

Crabs of the genus Uca Leach, 1814 are widely distributed along the Brazilian coast and play an important ecological role in the estuarine ecosystem in soil bioturbation, nutrient cycling and by serving as a food source for other organisms. This study analyzed the relationship of wet weight/carapace width and the temporal dynamics of the condition factor of the crab Uca mordax (Smith, 1870). The crabs were sampled manually on the bank of the Igaraçu River (02°53’58”S; 41°46’49”W) from September 2009 to June 2011, in the dry and rainy seasons. A total of 602 crabs (449 males and 153 females) were analyzed. The carapace width (CW) and the wet weight (WW) were determined for each individual. The biometric data obtained were submitted to a regression analysis using the power equation (y=axb). The CW/WW relationship for males was expressed by the equation WW=0.00011CW3.441, and for females by WW=0.000183.211. The condition factor was determined for each month and compared between the sexes. The females showed a 1.6 higher degree of fattening than the males. In the rainy season the females showed an isometric increase in weight, while the other relationships (males during the dry and rainy seasons and females in the dry season) showed a positive allometric increase. There was no significant difference in the degree of fattening between males and females.

Many animals that use acoustic communication synchronize their mate attraction signals: individuals precisely time their calls to overlap those of their neighbors. In contrast, synchrony in the mate attraction displays of species with visual/motion-based signals is rare. It has only been documented in five species of fiddler crabs. In all of them, small groups of males wave their single large claw in close synchrony. Here, I review what we know about synchrony in fiddler crabs, comparing the five species with each other to determine whether similar mechanisms and functions are common to all. I also propose future research questions that, if answered, would shed light on synchronous behavior in both visual and acoustic signallers. [ABSTRACT FROM AUTHOR]

Salt marshes in northern Barataria Bay, Louisiana, USA were oiled, sometimes heavily, in the aftermath of the Deepwater Horizon oil spill. Previous studies indicate that fiddler crabs (in the genus Uca) and the salt marsh periwinkle (Littoraria irrorata) were negatively impacted in the short term by the spill. Here, we detail longer-term effects and recovery from moderate and heavy oiling over a 3-year span, beginning 30 months after the spill. Although neither fiddler crab burrow density nor diameter differed between oiled and reference sites when combined across all sampling events, these traits differed among some individual sampling periods consistent with a pattern of lingering oiling impacts. Periwinkle density, however, increased in all oiling categories and shell-length groups during our sampling period, and periwinkle densities were consistently highest at moderately oiled sites where Spartina alterniflora aboveground biomass was highest. Periwinkle shell length linearly increased from a mean of 16.5 to 19.2 mm over the study period at reference sites. In contrast, shell lengths at moderately oiled and heavily oiled sites increased through month 48 after the spill, but then decreased. This decrease was associated with a decline in the relative abundance of large adults (shell length 21–26 mm) at oiled sites which was likely caused by chronic hydrocarbon toxicity or oil-induced effects on habitat quality or food resources. Overall, the recovery of S. alterniflora facilitated the recovery of fiddler crabs and periwinkles. However, our long-term record not only indicates that variation in periwinkle mean shell length and length-frequency distributions are sensitive indicators of the health and recovery of the marsh, but agrees with synoptic studies of vegetation and infaunal communities that full recovery of heavily oiled sites will take longer than 66 months.

Models proposed to explain sexually selected structures assume that these traits are costly. However, studies investigating the impact of such structures on locomotory costs have produced inconsistent results. Male fiddler crabs possess a large sexually selected clawand are ideal for assessing the impact of a sexually selected trait on the cost of locomotion. Here, we measured the energy expenditure of clawed, declawed and artificially loaded crabs during sustained exercise by measuring oxygen consumption and blood lactate levels. We also measured blood lactate levels of clawed and declawed crabs following a sprint and forced walk to assess energy expenditure during non-sustainable, strenuous locomotion. Clawed and declawed crabs consumed the same amount of oxygen and had the same blood lactate concentration during sustained locomotion, suggesting that the large claw does not increase energetic costs during sustainable locomotion. Following non-sustainable, strenuous locomotion, however, there was a trend for clawed crabs to have higher concentrations of lactate in their blood than declawed crabs, suggesting that bearing a large claw may increase energetic costs during strenuous locomotion and lengthen recovery time. Artificially loaded crabs produced more lactic acid than clawed and declawed crabs during sustainable locomotion, suggesting that compensatory traits help mitigate the energetic cost of carrying the large claw. Overall, our results show that the impact of exaggerated structures on energy expenditure may depend on exercise intensity and highlight the need to examine various locomotory intensities when attempting to assess the costs of bearing a sexually selected trait. [ABSTRACT FROM AUTHOR]

Fiddler crab burrow morphologies in tidal flat ecosystems depend largely on physical characteristics of the soil. Herein, we aimed to examine the relationship between soil texture profiles and the burrow depths and morphologies of four fiddler crab species: Tubuca arcuata , Gelasimus borealis , Xeruca formosensis , and Austruca lactea . We found that the burrow depths of T. arcuata , G. borealis , and A. lactea (range = 8–50 cm) were strongly affected by surface soil composition; only the burrow depth of X. formosensis (which reached 100 cm in some cases) was influenced by the presence of deeper, clay-rich soils. Specifically, X. formosensis relied more heavily on fine soils, such as clay or silt, when they burrowed deeper into sand-covered mudflats. We hypothesize that deep burrowers, such as X. formosensis, may coat clay-rich soils on their burrow walls to impede flooding and to prevent burrow collapse, suggesting that surface soil composition does not necessarily determine the burrow depth and composition for all fiddler crab species. [ABSTRACT FROM AUTHOR]

Courting males often perform different behavioural displays that demonstrate aspects of their quality. Male fiddler crabs, Uca sp., are well known for their repetitive claw-waving display during courtship. However, in some species, males produce an additional signal by rapidly stridulating their claw, creating a ‘drumming’ vibrational signal through the substrate as a female approaches, and even continue to drum once inside their burrow. Here, we show that the switch from waving to drumming might provide additional information to the female about the quality of a male, and the properties of his burrow (multiple message hypothesis). Across males there was, however, a strong positive relationship between aspects of their waving and drumming displays, suggesting that drumming adheres to some predictions of the redundant signal hypothesis for multimodal signalling. In field experiments, we show that recent courtship is associated with a significant reduction in male sprint speed, which is commensurate with an oxygen debt. Even so, males that wave and drum more vigorously than their counterparts have a higher sprint speed. Drumming appears to be an energetically costly multimodal display of quality that females should attend to when making their mate choice decisions.

Foraging fiddler crabs form a strict spatial relationship between their current positions and burrows, allowing them to run directly back to their burrows when startled even without visual contacts. Path integration (PI), the underlying mechanism, is a universal navigation strategy through which animals continuously integrate directions and distances of their movements. However, we report that fiddler crabs also use visual orientation during homing runs using burrow entrances as cues, with the prioritised mechanism (i.e. PI or visual) determined by the distance (which has a threshold value) between the goal, indicated by PI, and the visual cue. When we imposed homing errors using fake entrances (visual cue) and masking their true burrows (goal of PI), we found that frightened fiddler crabs initially ran towards the true burrow following PI, then altered their behaviour depending on the distance between the fake entrance and masked true burrow: if the distance was large, they kept running until they reached the true burrow, ignoring the visual cue; however, if the distance was small, they altered the homing path and ran until they reached the fake entrance. This suggests that PI and visual mechanism in fiddler crabs are mutually mediated to achieve their homing behaviour.

Many species worldwide are impacted by habitat loss. This may result in increased competition both within species and between species. Many studies have demonstrated that when two previously non-overlapping species are forced to compete over a resource, one species is likely to become dominant over the other. This study explores the impact a larger species of fiddler crab (Tabuca elegans—previously known as Uca elegans) has when invading an area previously used solely by a smaller species (Austruca mjoebergi—previously known as Uca mjoebergi). Here we show that, while there are some detrimental effects of living next to a heterospecific, they are relatively minor. New heterospecific neighbours fight more regularly with resident crabs, but each fight is no longer or more escalated than those between the resident and a new conspecific male. The residents are not specifically targeted by intruding heterospecifics, thus, given the large advantage of having a heterospecific neighbour in terms of lowered competition for females, the overall impact of species mixing is probably not as negative as might have been predicted.

Simulations in the laboratory were used to investigate whether survivorship rates of Ucides cordatus youngsters produced in the laboratory are significantly affected by other crab species after their release in natural environments. Furthermore, it was investigated whether the release of first instar juveniles instead of megalopae would reduce the mortality related to interspecific predation. A preliminary estimate of the crab community structure in the target area of a restocking program was undertaken and indicated a great dominance of fiddler crabs (Uca spp). Based on this information, experiments were conducted to assess the ecological relationship between Ucides cordatus megalopae and first instar juveniles and fiddler crabs of different size classes in the presence of mangrove sediment, simulating natural conditions, as well as in the absence of any kind of refuge. It was observed that fiddler crabs not only compete with, and prey on U. cordatus youngsters, both as megalopae and juveniles. Furthermore, it was observed that the predation behavior of fiddler crabs is exercised only by individuals with carapaces wider than 0.5 cm. The results of the assay simulating natural conditions showed that, even when sediment was provided as a refuge, the same pattern was observed, with survivorship rates significantly lower in the presence of Uca crabs.Simulações em laboratório foram efetuadas visando investigar se após liberação na natureza a sobrevivência de recrutas de Ucides cordatus produzidos em laboratório é afetada por outras espécies de caranguejos. Adicionalmente, foi verificado se com a liberação de juvenis no estágio 1, ao invés de megalopas, haveria redução da mortalidade causada por predação interespecífica. Para tanto foi realizada estimativa prévia da estrutura da comunidade de caranguejos presente na área-alvo de um programa de repovoamento em desenvolvimento na região de Santo Amaro, Baía de Todos os Santos, Brazil, cujos resultados mostraram grande dominância de caranguejos violinista (Uca spp.). Com base nessa informação, foram realizados experimentos para verificar as relações ecológicas entre megalopas e juvenis 1 de Ucides cordatus e as diferentes classes de tamanho das outras espécies de Uca, em presença de sedimento do mangue, simulando condições naturais, e na ausência de refúgio. Observou-se que os caranguejos violinista competem predando tanto juvenis quanto megalopas de Ucides cordatus. Além disso, foi visto que esse comportamento de predação é exercido apenas por indivíduos com largura de carapaça maior que 0,5 cm. Os resultados do teste de simulação das condições do ambiente natural evidenciaram que o mesmo padrão de predação foi observado mesmo quando o sedimento foi oferecido como refúgio, sendo as taxas de sobrevivência significativamente menores na presença de espécies de Uca.

Megalopae of many decapod crab species accelerate their development time to metamorphosis (TTM) when exposed to natural physical and/or chemical cues characteristic of the parental habitat. In the present study, the influence of natural settlement cues on the moulting rates and development TTM in megalopae of the fiddler crab Uca vocator was investigated. The effects of mud from different habitats (including well-preserved and degraded-polluted mangrove habitats) and conspecific adult 'odours' (seawater conditioned with crabs) on the induction of metamorphosis were compared with filtered pure seawater (control). 95 to 100% of the megalopae successfully metamorphosed to first juvenile crab stage in all treatments, including the control. However, the development TTM differed significantly among treatments. Settlement cues significantly shortened development, while moulting was delayed in their absence. The fact that megalopae responded to metamorphosis-stimulating cues originating from both adult and non-adult benthic habitats demonstrates that settlement in this species may occur in a wider range of habitats within the mangrove ecosystem, including impacted areas.Megalopas de muitas espécies de caranguejos decápodes aceleram seu período de desenvolvimento até a metamorfose (TOM) quando são expostas a estímulos naturais físicos e/ou químicos característicos do habitat parental. No presente estudo, a influência de estímulos naturais sobre as taxas de muda e sobre o PDM foi investigada nas megalopas do caranguejo violinista Uca vocator. Os efeitos da (i) lama de diferentes habitats (incluindo habitats de um manguezal bem preservado e de um degradado e poluído) e (ii) 'odores' dos adultos conspecíficos (água do mar acondicionada com caranguejos) sobre a indução da metamorfose foram comparados com (iii) água do mar pura e filtrada (controle). 95 a 100% das megalopas realizaram a metamorfose com sucesso para o primeiro estágio de caranguejo juvenil em todos os tratamentos, incluindo o controle. No entanto, o PDM diferiu significativamente entre os tratamentos. Os estímulos encurtaram significativamente o desenvolvimento, enquanto que a muda foi retardada na ausência deles. O fato de que as megalopas responderam aos estímulos indutores da metamorfose oriundos de ambos os habitats bentônicos dos adultos e de habitats onde eles são ausentes, demonstra que o assentamento nesta espécie pode ocorrer em uma grande variedade de habitats dentro do ecossistema de manguezal, incluindo áreas impactadas.

A population of the fiddler crab Uca rapax (Smith, 1870) found in Itaipu Lagoon, southeast Brazil, was sampled monthly from July 2006 to June 2007 in order to study population and reproductive features. The sex ratio of the population was statistically different from the expected (1:1) in almost every month, with a predominance of males. The reproductive cycle and the recruitment of juveniles were continuous, with two peaks. The fecundity ranged from 1.110 to 13.189 eggs (4.984 ± 2.493.8), not differing statistically among seasons. In contrast, the relative fecundity (F') and the reproductive intensity index (RII) were highest in the summer. Female size at the onset of sexual maturity was estimated as 6.1 mm and egg diameter ranged from 0.20 to 0.28 mm. The anthropogenic impact on the environment of Itaipu Lagoon probably had adverse effects on the local U. rapax population, as inferred by its low fecundity rates, early maturation age and biased sex ratio.

In order to evaluate their tolerance to low salinities, zoeae of the fiddler crab Uca tangeri from the Rio San Pedro population (southwestern Spain) were reared in the laboratory at 20ºC and at three salinities (16, 24 and 32). The zoeal development was completed at 24 and 32 but the crabs died as zoea I or zoea II, and very rarely as zoea III, at 16; tolerance to low salinities varied among clutches produced by different females. The duration of the first zoeal stage and of the complete zoeal development was shorter at 32. Our observations showed that the zoeae of U. tangeri could not tolerate retention in the mesohaline water of estuaries, and that export to oceanic waters would be optimal for their successful development. Survival at 24 suggests that larvae could also develop in polyhaline conditions if they were retained in the ocean-estuary interface. The presence of an additional zoeal stage (zoea VI) was observed in some individuals and associated with unfavourable combinations of temperature and salinity. In addition, some previously omitted aspects of zoeal morphology were re-described and illustrated, providing new evidence which supports the basal position of this species in a proto-Atlantic origin of the genus Uca. It is proposed that the differences between Uca tangeri and the rest of the Uca species should be highlighted, and that it should be placed in its own genus as Afruca tangeri.

Risks inherent in mate-searching have led to the assumption that females moving sequentially through populations of courting males are sexually receptive, but this may not be true. We examined two types of fiddler crab females: wanderers moving through the population of courting males and residents that were occupying and defending their own territories. Sometimes residents leave territories to look for new burrows and we simulated this by displacing wanderers and residents and observing their behaviour while wandering. We predicted that the displaced wanderers would exhibit more mate-searching behaviours than resident females. However, wandering and resident females behaved nearly identically, displaying mate-searching behaviours and demonstrating matching mate preferences. Also, males behaved the same way towards both female types and similar proportions of wanderers and residents stayed in a male's burrow to mate. But more wanderers than residents produced egg clutches when choosing a burrow containing a male, suggesting females should be categorized as receptive and non-receptive. Visiting and rejecting several males is not the defining feature of female mate choice. Moving across the mudflat by approaching and leaving a succession of burrows (mostly occupied by males) is an adaptive anti-predator behaviour that is useful in the contexts of mate-searching and territory-searching.

The influence of abiotic factors on the spatial distribution of the fiddler crabs Uca leptodactyla, U. maracoani, U. rapax and U. thayeri was studied in a tropical mangrove of northeast Brazil. Eight transects were delimited in a mangrove area of the Pacoti River. On each transect, three 0.25 m2 squares were sampled during spring low tide periods from September 2003 to August 2004. The sediment of the squares at each transect was analysed for grain size, organic matter and humidity. Morphology of the second maxilliped was studied considering the number of spoon-tipped setae to help explain the ecological distribution of the species. U. leptodactyla and U. rapax were found living in medium sand, U. thayeri was collected in fine and very fine sand, while U. maracoani was found living in very fine sand. U. leptodactyla showed a negative correlation with organic matter and humidity while U. thayeri showed a positive correlations for both factors. U. maracoani and U. rapax were not correlated with organic matter or humidity. The analysis of the second maxilliped revealed that U. leptodactyla and U. rapax show a high quantity of spoon-tipped setae while U. maracoani and U. thayeri show a greater quantity of plumose setae.

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.Fêmeas ovígeras de U. thayeri e de U. uruguayensis foram utilizadas para se avaliar e comparar o padrão reprodutivo. O tamanho médio das fêmeas foi de 6,6 ± 0,8mm para U. uruguayensis, variando de 17,3 ± 4,4mm para U. thayeri. A fecundidade média obtida para U. uruguayensis foi 1883 ± 490 ovos (N = 27) e para U. thayeri de 31068 ± 11185 ovos (N = 31). As diferenças observadas no padrão reprodutivo de U. thayeri e U. uruguayensis sugerem estratégias adaptativas: U. thayeri apresenta uma reprodução sazonal, com atividade pronunciada de janeiro a março e alta fecundidade, enquanto U. uruguayensis reproduz-se continuamente, mas com proles menores.