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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]

In iteroparous animals, it may be adaptive to adjust the amount of reproductive investment based on their current competitive ability. Male fiddler crabs use an enlarged major claw for claw-waving display in the breeding season. Males sometimes lose their claws, but they can regenerate a claw, which is an inferior weapon for male-male fights. Here, we compared the waving frequency between males with a regenerated claw (regenerated males) and with an original claw (original males) to examine the differences in the amount of reproductive investment. Regenerated males showed lower waving frequency than original males, but some regenerate males waved frequently before the optimal mating season where original males waved frequently. These results indicate that individuals with poor fighting ability that have lower chance of acquiring females invested less in waving, and may also have shifted their peak of mating period in order to avoid competition with original males. [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.

Males of the fiddler crab Austruca lactea exhibit drumming behaviour as vibroacoustic communication and wave their enlarged claw for courtship. However, we identified that they also perform drumming as an agonistic behaviour. To determine whether vibrational characteristics differ depending on context, we compared five drumming parameters (pulse rate, pulses per train, train duration, pulse duration and dominant frequency) between courtship and agonistic contexts. We found that courtship drumming had a longer train duration, with more pulses per train than agonistic drumming. However, agonistic drumming had a higher pulse rate than courtship drumming. Pulse duration and dominant frequency did not differ significantly between contexts. Therefore, fiddler crabs' vibrational signals might have evolved into two different signals, for agonistic and courtship interactions. • Male white-clawed fiddler crabs changed their vibrations depending on context. • Train duration was longer during courtship than during agonistic interactions. • Courtship drumming had more pulses per train than agonistic drumming. • Agonistic drumming had a faster pulse rate than courtship drumming. [ABSTRACT FROM AUTHOR]

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]

Macrobenthic bioturbation is vital to facilitate nutrient turnover in estuarine ecosystems and drives spatial heterogeneity in the sediment matrix. In this study, we compared the sediment physico-chemical properties, microbial community structure and functional genes in vertically-stratified sediment samples from bioturbated (burrows of Parasesarma bidens and Tubuca arcuata) and non-bioturbated area in mangrove ecosystems (the Hanjiang River Estuary, Southern China). The result indicated that bioturbation by P. bidens and T. arcuata had significantly different effects on sediment properties, with the action of P. bidens enhancing nutrient accumulation while T. arcuata promoted N 2 O emission. Burrow microhabitats harbored distinctive microbial communities although the dominant phylum and genera shared considerable similarity with the control sediment surface with Woeseia dominating in vertical profiles across different habitats. Co-occurrence network analysis revealed that crab bioturbation promoted formation of less complex but more functionally-specialized microbial communities. Crab bioturbation enhanced nutrient metabolism and separated clusters in dendrogram demonstrated the species-specific effect between P. bidens and T. arcuata. Our work verified the significance of bioturbators in regulating biogeochemical processes and highlighted the species-specific bioturbation effect between two dominant mangrove crabs (P. bidens vs. T. arcuata)., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

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%.

A great diversity of adaptations is found among animals with compound eyes and even closely related taxa can show variation in their light‐adaptation strategies. A prime example of a visual system evolved to function in specific light environments is the fiddler crab, used widely as a model to research aspects of crustacean vision and neural pathways. However, questions remain regarding how their eyes respond to the changes in brightness spanning many orders of magnitude, associated with their habitat and ecology. The fiddler crab Afruca tangeri forages at low tide on tropical and semi‐tropical mudflats, under bright sunlight and on moonless nights, suggesting that their eyes undergo effective light adaptation. Using synchrotron X‐ray tomography, light and transmission electron microscopy and in vivo ophthalmoscopy, we describe the ultrastructural changes in the eye between day and night. Dark adaptation at dusk triggered extensive widening of the rhabdoms and crystalline cone tips. This doubled the ommatidial acceptance angles and increased microvillar surface area for light capture in the rhabdom, theoretically boosting optical sensitivity 7.4 times. During daytime, only partial dark‐adaptation was achieved and rhabdoms remained narrow, indicating strong circadian control on the process. Bright light did not evoke changes in screening pigment distributions, suggesting a structural inability to adapt rapidly to the light level fluctuations frequently experienced when entering their burrow to escape predators. This should enable fiddler crabs to shelter for several minutes without undergoing significant dark‐adaptation, their vision remaining effectively adapted for predator detection when surfacing again in bright light. [ABSTRACT FROM AUTHOR]

Rate of mate sampling is one of the critical components associated with sampling costs in female mate choice. In ectotherms, environmental temperature generally constrains locomotion performance. In addition, females will adjust the mate sampling rate depending on their breeding schedule because of the risk of remaining unfertilized eggs or a loss of benefits related to mating, if they lose the opportunity to copulate. This study investigated how these effects influence the rate of female mate sampling in the temperate fiddler crab (Austruca lactea) in the field. The number of sampled males per searching duration formed a convex curve against environmental temperature. The optimal environmental temperature increased with the female body size. These results suggest that mate sampling rate is under a size-dependent temperature constraint, and sampling costs are lower for larger females than smaller individuals under high-temperature conditions. Furthermore, when there were fewer remaining days, the mate sampling rate increased. Females would hasten the sampling rate to ensure a suitable burrow for breeding. Mate sampling rate in female A. lactea is therefore associated with environmental temperature, female body size and remaining days until oviposition. [ABSTRACT FROM AUTHOR]

We examined copper accumulation in the hemolymph, gills and hepatopancreas, and hemolymph osmolality, Na+ and Cl− concentrations, together with gill Na+/K+-ATPase and carbonic anhydrase activities, after dietary copper delivery (0, 100 or 500 Cu µg g−1) for 12 days in a fiddler crab, Minuca rapax. In contaminated crabs, copper concentration decreased in the hemolymph and hepatopancreas, but increased in the gills. Hemolymph osmolality and gill Na+/K+-ATPase activity increased while hemolymph [Na+] and [Cl−] and gill carbonic anhydrase activity decreased. Excretion likely accounts for the decreased hemolymph and hepatopancreas copper titers. Dietary copper clearly affected osmoregulatory ability and hemolymph Na+ and Cl− regulation in M. rapax. Gill copper accumulation decreased carbonic anhydrase activity, suggesting that dietary copper affects acid–base balance. Elevated gill Na+/K+-ATPase activity appears to compensate for the ion-regulatory disturbance. These effects of dietary copper illustrate likely impacts on semi-terrestrial species that feed on metal-contaminated sediments. [ABSTRACT FROM AUTHOR]

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.

Many intertidal species are expanding their distribution limits towards the poles as a consequence of increased temperature due to climate change. At the same time, some intertidal habitats have been reduced due to rising sea levels. Fiddler crabs inhabit mangroves, and different species occupy well-established zones. Due to the restricted mangrove areas and consequent latitudinal expansion of the species, the distribution and density of fiddler crabs may be subject to change. The overlap forces several species to cohabit in a smaller territorial space. Fiddler crab species can vary in size, which could decisively affect territorial competition. Using Leptuca urguayensis as a reference, we tested how competing species of different sizes (larger size: L. thayeri and Minuca panema ; similar size: L. cumulanta and L. leptodactyla) might interact in future climate change scenarios. First, we showed that within the territory of L. uruguayensis , the species L. cumulanta and L. thayeri occurred mainly in the lower mesolittoral zone, while L. leptodactyla and M. panema predominated in the upper mesolittoral zone. In a laboratory experiment, we evaluated whether the density and size of the heterospecific competitors could alter the agonistic behavior of Leptuca uruguayensis. Our results indicated that increasing the density can increase the agonistic behavior of L. uruguayensis with a greater intensity against species of a similar size. In a second field experiment, we demonstrated that the presence of a burrow enhances the intensity of agonistic interactions between L. uruguayensis and species of similar size. Therefore, in a scenario of territorial expansion of fiddler crabs due to climate change, it is expected that similarly sized species represent a greater competitive threat to populations of L. uruguayensis. [Display omitted] • Six fiddler crab species showed differential distribution along intertidal zone microhabitats. • Leptuca uruguayensis exhibits different levels of agonistic behaviors according to the size of its adversary. • The increase in density due to the overlapping of territories can increase the agonistic behavior of L. uruguayensis. • The burrow is a resource that increases the intensity of agonistic interactions between fiddler crab species of similar sizes [ABSTRACT FROM AUTHOR]

The anthropogenic construction activities on the coasts, such as pile-driving, generate vibrations that propagate through the substrate. Such substrate-borne vibrations could potentially affect marine organisms inhabiting the benthic environments. However, there is a lack of documented studies on the effects of vibrations on benthic animals. To investigate whether anthropogenic substrate-borne vibrations such as pile-driving operation influence the fiddler crab, Austruca lactea , we measured their locomotion response under vibrations of 35, 120, 250, 500, and 750 Hz generated by a vibrator. We compared the locomotion of crabs between control and vibration-treatment groups using videography. The duration of movements was significantly lower under 120 Hz vibrations compared to the control. Moreover, crab velocity was significantly higher under vibrations of 120 Hz and 250 Hz compared to the control group. Our result suggests that A. lactea can detect low-frequency substrate-borne vibrations and experience stress, leading to increased energy consumption. [Display omitted] • Fiddler crabs can detect low-frequency (120–250 Hz) substrate-borne vibrations. • Austruca lactea reduced movement duration or increased velocity to such vibrations. • The locomotion of them suggests that such vibrations could pose a stressor. • Vibrational disturbances should be considered for coastal construction. [ABSTRACT FROM AUTHOR]

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]

The decision to take risks in the presence of a predator involves complex trade-offs between immediate survival and future reproduction. Individuals may gain fitness advantages if they are able to optimally alter their risk-taking strategies depending on the differential costs and benefits of risky behaviours across contexts. Male fiddler crabs (Austruca mjoebergi) exhibited a higher propensity to take risks in the presence of a female compared with conspecifics that were not presented with a female during both mating and nonmating periods. Contrary to predictions, however, risk-taking behaviour did not differ between mating and nonmating periods. • Risk taking can involve trade-offs between survival and future reproduction. • Altering risk-taking strategies optimally across contexts may enhance fitness. • Male crabs altered their risk-taking behaviour across contexts. • Males took the most risks in the direct presence of a female. [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]

Minuca mordax is a model for studies on ocean acidification and sea-level rise because lives in mangroves and riverbanks with low pH. We investigated the physiology of the crabs exposed to differents pH (6.5 and 5.8) and salinity (25, 30, 35, 40 45S). There was not mortality or alterations in the hypo-osmoregulation, suggesting that the factors did not affect salt absorption/secretion. Reduced pH changed metabolism, ammonia excretion, and hepatosomatic index in relation to the animals kept in control pH. At elevated salinities, metabolism increased when animals were kept in control pH, but it decreased when they were exposed to acidified pH. energy substrate, varied between proteins to a mixture of proteins and lipids. Important physiological parameters, related to the catabolism of amino acids and to the energy demand are changed and the consequences might include alterations in growth and reproduction due to the energy channeling to limiting processes of homeostasis. [ABSTRACT FROM AUTHOR]

The services and functions provided by coastal wetlands are numerous and influenced by factors ranging from climate and tidal regime to ecosystem engineers and anthropogenic modifications. In New England salt marshes, fiddler crabs and purple marsh crabs are cooccurring species that are among the most conspicuous burrowing macroinvertebrates in the region. Both are known to influence salt marsh ecosystem functions through their burrowing and feeding behavior, but the ways in which they regulate specific properties, individually and together, is unclear. Using an ex situ mesocosm study, I manipulated the presence of fiddler crabs and purple marsh crabs in order to evaluate their impact on several soil properties and aboveground biomass. Results show that, contrary to previous studies, the fiddler crab had little impact while the purple marsh crab altered soil quality with positive implications for plant growth. This suggests that the purple marsh crab, known to be a voracious consumer of marsh vegetation, may play a much more nuanced role in the maintenance of plant growth than previously thought. Additional ex situ studies should be done to further delineate the impact of these two species. [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]

Abstract Autotomy is a predator escape mechanism in many taxa, including crustaceans. Male fiddler crabs autotomize the major claw, despite its importance in mating, territoriality, and thermoregulation. This claw can be regenerated through molting. We investigated major claw autotomy in the fiddler crab Leptuca pugilator , testing hypotheses that (1) autotomy of the major claw accelerates the molting process, reflecting the importance of this appendage, (2) autotomy of the major claw results in increased feeding to accumulate energy reserves needed for regeneration, (3) this change in feeding is hormonally driven. Autotomy of the major claw accelerated molting. Yet contrary to expectations, autotomy of the claw initially inhibited feeding, with evidence for release of feeding inhibitory factor. These effects are specific to the major claw, and were not seen following autotomy of a walking leg. Acceleration of molting following autotomy of the major claw appears to be an adaptive response reflecting the costs of being without this multi-function structure. Highlights • We investigated major claw autotomy in the fiddler crab Leptuca pugilator. • Autotomy of the major claw accelerated molting. • Autotomy of the major claw reduced feeding behavior for at least 96 h. • Autotomy of a walking leg had no effect on molting or feeding. • Results represent an adaptive response reflecting the costs of losing the major claw. [ABSTRACT FROM AUTHOR]

Abstract Current climate change directly affects species distribution by altering their physical environment and indirectly by altering interspecific interactions. The geographical distribution of fiddler crabs, keystone species of intertidal estuarine sediments, is supposed to expand poleward as a response to climate change. We experimentally investigate whether the introduction of a new species of fiddler crabs, where another different species already occurs, may affect the structural and functional composition of meiobenthic communities in intertidal areas. In order to disentangle the effect of abundance from species identity, we set up two indoor experiments (substitutive and a partial additive design) manipulating the diversity and density of two keystone species, Leptuca uruguayensis and L. leptodactyla. The results showed that the increase of the diversity keystone species did not impact any measured descriptors of nematode assemblages. By contrast, high density of keystone species, independent of the species, strongly affected the meiofauna total density, and the density of numerically dominant nematode genera. The results did not reveal any functional change in the meiofauna. Our experiments, designed to mimic the indirect effects of range expansion showed that while increasing diversity of functionally redundant keystone species had no effect on preys, increasing density negatively affected the structure of intertidal habitats. [ABSTRACT FROM AUTHOR]