Fiddler Crab Uca Research Articles

Eye Movement Reflexes Indicate the Homing Direction in the Path-Integrating Fiddler Crab, Uca pugilator

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.

Genetic Structure of the Endemic Fiddler Crab Uca (Xeruca) formosensis on the West Coast of Taiwan.

Xeruca formosensis is the only endemic species of fiddler crab on the west coast of Taiwan. However, its natural habitats and populations have been compromised by excessive anthropogenic activities and improper land use over the past four decades. In light of these changes, we sought to evaluate the genetic diversity and gene flow of the species by examining the genetic variation of X. formosensis at different sampling locations. To this end, we performed molecular analyses of three endonuclease-amplified fragment length polymorphisms (TE-AFLP) and the cytochrome oxidase subunit I (COI) marker from leg muscle samples. We found that the genetic variation within sampling locations was higher than that among sampling locations, and the expected heterozygosity of genetic diversity (Hj) was 0.152 for TE-AFLP data. Meanwhile, the COI marker showed high haplotype diversity (h = 0.976 ± 0.008) and a low genetic differentiation level (FST = 0.021) in X. formosensis populations. Importantly, the genetic connectivity of X. formosensis may be influenced by larval-stage crabs drifting between coastal and marine habitats. As such, crab gene flow is promoted among populations by larval exchange via nearshore currents. Although X. formosensis has high gene flow, the species could undergo an extinction crisis if the population sizes continue to decline, as with most endangered species. In order to maintain the natural habitats and population size of X. formosensis, long-term monitoring and investigation will be necessary.

Fecundity and reproductive patterns of the fiddler crab Uca maracoani Latreille 1802-1803 in an Amazonian estuary in northern Brazil

ABSTRACT In this study, aspects of the reproductive biology of a Uca maracoani population from northern Brazil were examined. Ovigerous females monthly captured from December 2013 to November 2015 were measured and dissected to count, collect morphometric data, and classify the eggs. Ovigerous females were encountered throughout the two-year period but were absent during the months with the highest rainfall and lowest salinity, which indicates a seasonal–continuous reproductive pattern. The fecundity varied from of 12,233 to 85,000 eggs per female, and mean was 36,840 ± 3,361 eggs. The egg size increased progressively and significantly over the course of embryonic development. We found a direct relationship between the size of the females and their fecundity, and a clear trend was seen in which the larger females produced more eggs with larger sizes, which increased less in size during embryonic development. The presence of early- and late-stage eggs together in the same ovigerous mass in a considerable number of the ovigerous females suggests multiple spawning. The fecundity of U. maracoani is greater than that of other Atlantic fiddler crab species, and its reproductive strategy ensures its survival in the estuaries of the Amazon coast, which are subject to considerable fluctuations in salinity.

Commentary on: Shell use by juvenile fiddler crabs Uca pugnax and Uca pugilator by George, Carlson and Regassa

Commentary on: Shell use by juvenile fiddler crabs Uca pugnax and Uca pugilator by George, Carlson and Regassa

Population biology of the fiddler crab Uca maracoani (Crustacea, Ocypodidae) inhabiting an impacted mangrove area on the southern coast of São Paulo state, Brazil

Fiddler crabs are important components of intertidal benthic macrofauna in estuarine habitats. However, these invertebrates often inhabit areas under anthropogenic-driven changes. In this study, we evaluated the habitat quality and the population biology of the fiddler crab Uca maracoani (Latreille, 1802) in a mangrove area under anthropogenic influence, on the southern coast of São Paulo state, Brazil. Sediment samples for ecotoxicological analyses and data on the population biology of U. maracoani were collected monthly between October 2008 and October 2009. Contamination was observed in sediment samples from all months, indicating that benthic organisms inhabiting the study area are continuously exposed to toxicity. The sex ratio did not deviate from 1:1 for the whole population of U. maracoani, within any given month (except in October 2008, when males outnumbered females). Adult males and females showed a similar size, while juvenile females were larger than juvenile males, probably reflecting that females attained sexual maturity at a larger size than males. For both juvenile and adult stages, the major cheliped propodus length and height in males and the abdomen width in females showed positive allometry. The size-frequency distribution of the studied population varied from unimodal to bimodal. Juveniles were recorded in all months, suggesting the studied population has continuous recruitment. In contrast, ovigerous females were not found in the study area for several months. Although U. maracoani is continuously exposed to contamination present in the sediment, it presents a well-established population and seems to persist in the study area.

Bioaccumulation and biomagnification of potential toxic elements (PTEs): An Avicennia germinans–Uca rapax trophic transfer story from Jobos Bay, Puerto Rico

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.

Complete mitogenome of Uca rosea and Uca paradussumieri, and their implications in evolution history of fiddler crab in Ocypodidae

We determined the complete mitogenomes of two fiddler crabs Uca rosea (15,643 bp) and Uca paradussumieri (15,614 bp) of Ocypodidae within Brachyura. Both consist of 37 genes (13 protein-coding genes (PCGs), two ribosomal RNA genes, 22 transfer RNA genes and one control region). The mitogenomes composition of U. rosea and U. paradussumieri are highly A + T biased, 70.77% and 71.12%, respectively, and showed positive AT (0.03 and 0.02) and negative GC (−0.29 and −0.24) skews. Phylogenetic analysis showing all the fiddler crabs were under monophyletic group relationship and belong to Ocypodidae; U. rosea has a sister group relationship with U. paradussumieri.

Uca maracoani (Crustacea, Decapoda, Ocypodidae) from a Miocene paleomangrove in Brazil: A case of evolutionary stasis among tropical American fiddler crabs

The Miocene fiddler crab Uca maracoani antiqua Brito, 1972, from the Pirabas Formation (Brazil), has been recurrently claimed to be a valid species and the oldest fossil record of the brachyuran crab family Ocypodidae. However, morphological investigations with the aid of microCT scan images of a large number of topotypic specimens and re-examination of the type material of U. maracoani antiqua revealed that it should actually be merged into the synonymy of Uca (Acanthoplax) maracoani (Latreille, 1802). Therefore, U. maracoani, the morphology and ecological traits of which have persisted essentially unchanged for at least 16 Ma (Burdigalian to present), is actually a long-lived crab species inhabiting an estuarine, sheltered mudflat environment that, likewise, has essentially remained unchanged. Burgeoning evidence suggests that evolutionary stasis may not be uncommon among mangrove crabs, as revealed by Afruca tangeri (Eydoux, 1835) from the middle Miocene in northeastern Spain and U. ornata (Smith, 1870) from the Plio-Pleistocene in Honduras. Uca antiqua is redescribed and illustrated based on 3D volume reconstruction and several topotypic specimens. The microCT analysis revealed a considerable number of fossil concretions of U. maracoani, with both males and females likely sharing the same burrow. This is the first fossil record of a male fiddler crab with a female inside a burrow, where mating usually takes place. This mating style is common to almost all extant American fiddler crabs.

Unidirectional Optomotor Responses and Eye Dominance in Two Species of Crabs.

Animals, from invertebrates to humans, stabilize the panoramic optic flow through compensatory movements of the eyes, the head or the whole body, a behavior known as optomotor response (OR). The same optic flow moved clockwise or anticlockwise elicits equivalent compensatory right or left turning movements, respectively. However, if stimulated monocularly, many animals show a unique effective direction of motion, i.e., a unidirectional OR. This phenomenon has been reported in various species from mammals to birds, reptiles, and amphibious, but among invertebrates, it has only been tested in flies, where the directional sensitivity is opposite to that found in vertebrates. Although OR has been extensively investigated in crabs, directional sensitivity has never been analyzed. Here, we present results of behavioral experiments aimed at exploring the directional sensitivity of the OR in two crab species belonging to different families: the varunid mud crab Neohelice granulata and the ocypode fiddler crab Uca uruguayensis. By using different conditions of visual perception (binocular, left or right monocular) and direction of flow field motion (clockwise, anticlockwise), we found in both species that in monocular conditions, OR is effectively displayed only with progressive (front-to-back) motion stimulation. Binocularly elicited responses were directional insensitive and significantly weaker than monocular responses. These results are coincident with those described in flies and suggest a commonality in the circuit underlying this behavior among arthropods. Additionally, we found the existence of a remarkable eye dominance for the OR, which is associated to the size of the larger claw. This is more evident in the fiddler crab where the difference between the two claws is huge.

Large‐scale ecosystem engineering by flamingos and fiddler crabs on West‐African intertidal flats promote joint food availability

Although the ecosystem engineering concept is well established in ecology, cases of joint engineering by multiple species at large scales remain rare. Here, we combine observational studies and exclosure experiments to investigate how co‐occurring greater flamingos Phoenicopterus roseus and fiddler crabs Uca tangeri promote their own and each other's food availability by creating a spatially complex mosaic of depressions (bowls, gullies) and hummocks (plateaus, mounds) in the intertidal zone. This results in a mosaic of microhabitats with different tidal inundation regimes. These microhabitats are spatially organized with labyrinth‐like patterns in the high intertidal zone and spotted patterns in the lower intertidal, both of which likely arise from biophysical interactions between these organisms and hydrodynamic forces. We show that the resulting spatial complexity is vital for biofilm production. The depression microhabitats were wetter and richer in organic matter and biofilms compared with hummocks. Excluding flamingos and crabs resulted in an increase in biofilm biomass over the shorter term (six months), but a decrease over the longer term (after one year). Moreover, our results strongly suggest that these biogeomorphological microhabitats in the mosaics were maintained by the feeding activities of flamingos and to a lesser extent crabs. During a period of flamingo exclusion, all the spotted patterns filled up with sediment, while the exclusion of crabs led to gradual sediment accumulation in the labyrinth‐like patterns. Collectively, these findings provide empirical evidence for large‐scale joint promotion of food availability by multiple taxa in a marine ecosystem.

Impact of pollution on the feeding, bioturbation and biomass of Uca annulipes in Gazi and Mikindani mangroves, Kenya

Owuor MA, Aloo-Obudho P, Cannicci S, Gitundu JK. 2017. Impact of pollution on the feeding, bioturbation and biomass of Uca annulipes in Gazi and Mikindani mangroves, Kenya. Ocean Life 1: 61-68. Marine pollution is one of the main anthropogenic factors globally recognized that affect the estuarine and coastal ecosystems. Mangroves received the pollutant since they are intercepting between land and ocean. Despite the utilization of natural mangrove as pollution buffers, how these pollutants might impact the biodiversity of the ecosystems remains a great question. Here, we aimed at determining the impact of pollution on the feeding, bioturbation, and biomass of the fiddler crab Uca annulipes in two regions, Gazi and Mikindani, all along the Kenya Coast. The mangroves in Mikindani on Tudor creek represented peri-urban mangroves that are heavily impacted by municipal wastewater. Meanwhile, the mangroves in Gazi Bay in the South Coast of Kenya served mangroves not affected by direct sewage input. Furthermore, Crabs U. annulipes are one of the most important groups of mangrove epifauna. We adopted a stratified nested design to investigate the impacts of pollution on the feeding, bioturbation, and biomass of U. annulipes. We applied a layered random sampling approach at each site that spanned in 2 × 2 m2 quadrats in desert and Avicennia zones during July, August and October 2005. The data collection depended on each full moon springs and new moon springs. Different parameters were measured, chlorophyll a (Chl a) concentrations in the feeding pellets and unprocessed soils, amount of bioturbated clays (expressed as dry weight of excavated material and feeding pellets), and biomass (dry weight) of U. annulipes. Four-factor Analysis of Variance (ANOVA) tests were applied to determine whether there was a significant difference in feeding, bioturbation, and biomass of U. annulipes within the two sites. Our findings show substantial differences in chlorophyll a concentration in the feeding pellets in the Avicennia zone of the peri-urban mangroves. Moreover chlorophyll a level did not vary between the processed and unprocessed soils in the Avicennia zone. In Gazi, a significant difference in the bioturbated material was recorded compared to Mikindani. The results demonstrate a consistent increase in crab biomass at the peri-urban site, then the non-urban mangroves. The Avicennia zone of the suburban location had a higher U. annulipes biomass compared to the non-urban Gazi. There was no association between the mass of bioturbated material and Uca biomass. The results also show that the amount of excavated material did not relate to the Uca biomass.

New record and range extension of the fiddler crab Uca princeps (Smith, 1870) (Brachyura, Ocypodidae) from California, USA

New record and range extension of the fiddler crab Uca princeps (Smith, 1870) (Brachyura, Ocypodidae) from California, USA

Mudflat Use and Predation on Male Southwestern Atlantic Fiddler Crabs (Uca uruguayensis) by Gull-billed Terns (Gelochelidon nilotica)

Abstract. Gull-billed Terns (Gelochelidon nilotica) comprise a group of cosmopolitan subspecies that make use of a wide range of aquatic ecosystems and have a broad dietary spectrum. This study documents the use of a southwestern Atlantic mudflat in Argentina and depredation of the southwestern Atlantic fiddler crab (Uca uruguayensis) by Gull-billed Terns. Gull-billed Terns preyed exclusively on male fiddler crabs. This may have been due to the observed presence of Gull-billed Terns mainly between 2 and 3 hr after low tide, when more than 80% of fiddler crabs active on the surface were males. Gull-billed Terns spent 66.9% of the time flying over and feeding on fiddler crabs. Gull-billed Terns landed without feeding 9.3% of the time. Gull-billed Terns succeeded in capturing prey in 29.8% of cases. Food capture rate of Gull-billed Terns was 68.9 items/hr, which is higher than rates reported for the species feeding on fiddler crabs in Mauritania and Guinea Bissau.

Crude oil toxicity to fiddler crabs (Uca longisignalis and Uca panacea) from the northern Gulf of Mexico: Impacts on bioturbation, oxidative stress, and histology of the hepatopancreas.

The intensive drilling and extraction of fossil fuels in the Gulf of Mexico result in a considerable risk of oil spills impacting its coastal ecosystems. Impacts are more likely to be far-reaching if the oil affects ecosystem engineers like fiddler crabs, whose activities modify biogeochemical processes in the sediment. The present study investigated effects of oil on the fiddler crabs Uca longisignalis and Uca panacea, which are important as ecosystem engineers and as prey for a wide variety of species. The present study used mesocosms and microcosms to investigate the effects of crude oil on fiddler crab burrowing and to assess cellular and tissue damage by the oil. Fiddler crabs were exposed for periods of 5 or 10 d to oil concentrations up to 55 mg/cm2 on the sediment surface. Their burrowing was delayed, their burrows were smaller, and they transported less sediment in the presence of oil. The hepatopancreas had elevated levels of oxidative stress and a higher abundance of blister cells, which play a role in secretory processes. Interspecific differences were observed; most effects were strongest in U. panacea, though burrowing was more strongly affected in U. longisignalis. The present study demonstrates that crude oil is likely to impact fiddler crabs and many species that depend on them for their diet or for the ecological changes that result from their burrowing. Environ Toxicol Chem 2018;37:491-500. © 2017 SETAC.

The effect of abrupt salinity change on oxygen consumption in crab megalopae of Chincoteague Bay, USA

Variability in salinity is an environmental stressor that crab megalopae encounter as they are carried by tides and currents throughout Chincoteague Bay. We exposed blue crab (Callinectes sapidus) and fiddler crab (Uca spp.) megalopae to abrupt salinity changes from 10 to 31 ppt and measured their oxygen usage. It was hypothesized that the megalopae would cope with the changes in a manner reflective of the documented abilities and tolerances of adult crabs. It was also hypothesized that lower salinities would have a particularly detrimental effect on the megalopae reflected by both increased oxygen usage and mortality. The megalopae of both species did exhibit an increase in oxygen use at lower salinities, although the effect was more pronounced during the initial transition and decreased during acclimation. The megalopae mirrored the adult responses, with blue crab larvae consuming more oxygen per mg of wet weight at lower salinities, whereas fiddler crab larval oxygen consumption was relatively uniform at all salinities. Mortality of some blue crab postlarvae was observed at 10 ppt while all larval fiddler crabs survived. Coupled with the introduction of additional fresh water into the global water system, these results indicate that further investigation into this subject is necessary.

Seasonal and latitudinal variations in the energy reserves of the mud fiddler crab Uca pugnax: implications for the response to climate change

Seasonal and latitudinal variations in the energy reserves of the mud fiddler crab Uca pugnax: implications for the response to climate change

First record of the Bengal fiddler crab Uca (Austruca) bengali Crane, 1975 (Braychura: Ocypodidae) from Kuakata National Park, Bangladesh

Abstract not available
 Dhaka Univ. J. Biol. Sci. 26(2): 199-203, 2017 (July)

Testing female preferences under more natural conditions: a case study on a fiddler crab

Mate choice is often affected by multiple factors, and there are often trade-offs associated with choosing a mate. Additionally, experiments that test for mate preferences usually rely on simple two-choice tests. These tests are, however, often less complex than the scenarios that individuals face in natural populations. Here, we test female choice in the fiddler crab Uca mjoebergi. We looked at female preference for wave rates and proximity to males in simple two-choice tests. We then mimicked a more natural choice scenario, where females faced a cluster of six courting males that differed in their distance from the female as well as in their wave rate. In addition, we tested whether female preferences under these more complex conditions were affected by the risk of predation. We found a preference for faster wave rates and closer males in two-choice tests. The preference for closer males was, however, only evident when the difference in distance was large (15 cm), not when it was small (3 cm). When females chose between six males, they preferred the males that waved faster, even if they were further away. We did not, however, find any difference in female choice when a simulated predator was present or absent. By examining a more realistic set of options that females face, we can paint a better picture of how females’ trade-off costs and benefits during mate choice. Mate choice experiments often rely on two-choice tests. Mate choice, however, is often more complex under totally natural conditions. Using a two-choice experiment, we show that female fiddler crabs U. mjoebergi show a preference for faster wave rates and closer males. Under a more natural choice scenario, when choosing between six males, females preferred to travel longer to reach faster waving males. We found that female responses did not differ when a predator was present or absent. Designing choice experiments to more accurately mimic natural conditions will allow assessing trade-offs that occur in mate choice.

Social cues affect synchronization of male waving displays in a fiddler crab (Crustacea: Ocypodidae)

The influence of social context in animal signals can lead to complex communicational patterns. In particular, the interaction between individuals can lead to intriguing collective dynamics, such as the temporal synchronization of signals. A fascinating example of such temporal synchronization involves the waving displays of fiddler crabs, in which males raise and lower their enlarged claws in species-specific rhythms. The adaptive significance of this phenomenon is still obscure, but possibly involves female preference for leading waving displays. However, waving displays are highly complex social signals that might be involved in a variety of forms of communication other than simply attracting females, but little is known about the influence of social context on wave synchronization. In this study we carried out field experiments to investigate the effect of two social factors, male density and female presence, on the level of waving synchronization in the fiddler crab Uca leptodactyla. Groups of males at varying densities were established in enclosures and recorded either in the presence or absence of a female. Our results indicate that the main factor driving synchronization is the presence of the female, with males not only changing the timing of their waving displays, but also altering their spatial distribution in the arenas. On the other hand, male density had a negligible effect on synchronization (despite significantly increasing waving rate), suggesting that male–male communication plays a minor role in the emergence of waving synchronization in this species.

Burrow excavation and mudballing behaviour of the fiddler crab Uca annulipes (H. Milne Edwards, 1837) from southern Thailand

We video-recorded and examined the burrow building behaviour of small and large males and females of Uca annulipes (H. Milne Edwards, 1837). Males took a longer time than females, and larger crabs took a longer time than smaller ones, to build burrows. Higher numbers of mudballs were excavated from inside the burrows during the build of the burrows by males than by females, and by larger crabs than by smaller ones. Crab carapace width was positively correlated with the time required to build burrows, and with the number of mudballs excavated from inside the burrows during the build of these burrows. We observed that 82% of the females placed the mudballs near their burrow entrance, whereas 85% of the males placed the mudballs far from their burrow entrance. After building the burrows, 71% of the females went inside the burrow and plugged the burrow entrance, and 90% of the males foraged for food.