Soldier Crabs Research Articles

How do soldier crabs behave when seeing vibrating robots?

Metaheuristic algorithms are a method of searching for a suboptimal solution and are implemented by a large number of agents, such as a swarm of animals. In this method, it is very important to adjust the relationships and/or interplay between individual freedoms and constraints as a group. The phenomena related to this interplay are strongly relevant for self-organized criticality showing a power law distribution. Since individuals’ independent behavior and translation as a group coexist in a swarm of soldier crabs, we conducted an experiment involving soldier crabs to estimate whether a power law distribution results from that interplay. The engine of translation was implemented by the directed movement of robot crabs. Soldier crabs confronting moving robot crabs were observed in the experiment. Here, we show that the interaction between robots and soldier crabs entails a Lévy walk characterized by a power law distribution of step length as well as the real swarm. This result suggests that soldier crabs could be attracted by the directed motion of robots and that combining a random walk with ballistic movement can realize a Lévy walk.

The complete mitogenome of the Thai soldier crab Mictyris thailandensis Davie, Wisespongpand & Shih, 2013 (Crustacea: Decapoda: Mictyridae)

Mictyris thailandensis has been described recently in the family Mictyridae which is found only in the Andaman Sea, west coast of Thailand. In this study, we performed shotgun genome sequencing of a male M. thailandensis using a paired-end (150 bp) sequencing chemistry on MGISEQ-2000RS and report the complete mitochondrial genome of M. thailandensis (15,557 bp). A total of 37 genes have been annotated: 13 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), two ribosomal RNA genes (rRNAs), and a control region. Comparative phylogenetic analysis with 29 crustaceans based on 13 conserved genes demonstrated that M. thailandensis is closely related to other soldier crabs in the family Mictyridae. The mitogenome of M. thailandensis presented here provides useful genetic information to help understand the evolutionary relationships among the Mictyridae family members.

Burrowing-site selection by the soldier crab Mictyris guinotae Davie, Shih & Chan, 2010 (Decapoda: Brachyura: Mictyridae)

AbstractThe soldier crab Mictyris guinotae Davie, Shih & Chan, 2010 inhabiting sandy tidal flats in the Ryukyu Is., Japan, are deposit feeders in two regions: its upper habitat where it burrows and the shoreline. The crabs usually migrate between these two regions during the period of emergence at the daytime and night-time low tide. The aim of this study was to determine which kind of sediments are chosen by the crabs when burrowing. Experiments designed to investigate burrowing-site selection revealed that the crabs preferably burrowed in sediment that had been conditioned through feeding by conspecific crabs, but not in sediment that had been conditioned by conspecific crabs walking on its surface. Moreover, the crabs never showed any preference for burrowing in sediment that had been conditioned through feeding by the competitor fiddler crab Austruca perplexa (H. Milne Edwards, 1852); both soldier (prey) and fiddler (predator) crabs sympatrically inhabit the tidal flat, but segregate their habitats with a transition area. These results suggest that chemical cues in sediment conditioned through feeding by conspecific soldier crabs affect where crabs burrow.

Inverse Bayesian inference in swarming behaviour of soldier crabs.

Animals making a group sometimes approach and sometimes avoid a dense area of group mates, and that reveals the ambiguity of density preference. Although the ambiguity is not expressed by a simple deterministic local rule, it seems to be implemented by probabilistic inference that is based on Bayesian and inverse Bayesian inference. In particular, the inverse Bayesian process refers to perpetual changing of hypotheses. We here analyse a time series of swarming soldier crabs and show that they are employed to Bayesian and inverse Bayesian inference. Comparing simulation results with data of the real swarm, we show that the interpretation of the movement of soldier crabs which can be based on the inference can lead to the identification of a drastic phase shift-like transition of gathering and dispersing.This article is part of the theme issue ‘Dissipative structures in matter out of equilibrium: from chemistry, photonics and biology (part 2)’.

Visual image of neighbors to elicit wandering behavior in the soldier crab

The soldier crab appears in great numbers and feeds while wandering during daytime low tide. When they see an approaching object, they screw themselves into the sand. The mechanism of formation of mass wandering has not been clarified. In this study, to investigate if the soldier crabs use visual images of neighbors as a stimulus for wandering, dummy crabs were presented to crabs. In the experiments, one, two, four, or eight dummies were placed in a circle on a sand arena. Each crab was placed in the center of the arena and observed whether it burrowed into the sand or wandered. The proportions of wandering individuals in each experimental treatment were compared with the expected value. Significantly more crabs were wanderers when only two and four dummies were present. This result suggests that soldier crabs chose burrowing or wandering depending on visual image of the distribution of the neighbors.

Meiofauna and crabs in mangroves and adjoining sandflats: Is the interaction physical or trophic?

Meiofauna distribute widely in most soft substrates in the marine and freshwater realms. Given their small body size (63 to 500μm) and high density, meiofauna are potential food items for predators such as deposit-feeding brachyuran crabs. Crab bioturbation may also affect meiofaunal assemblages through effects such as translocation to unsuitable microhabitats. This study aimed to investigate the significance and nature of top-down control on the density of meiofauna based on their interactions with deposit-feeding crabs in a mangrove and adjoining sandflat; specifically, whether the interaction is primarily physical or trophic. Field manipulative experiments were conducted within the aggregation zones of soldier crabs (Mictyris longicarpus) and fiddler crabs (Uca vomeris) in a mangrove-lined creek in Southeast Queensland, Australia. Meiofaunal density in five experimental cage treatments (Exclusion, Inclusion with complete crab (‘Inclusion’), Inclusion with ‘disabled’ crab (feeding claw removed, ‘Disabled’), Half-cage, and Ambient) was compared. Removal of soldier crabs from the cages (Exclusion) increased meiofaunal density (426±46 ind./10cm2; mean±SE) by 50% over that in the Inclusion treatment (283±22). The nature of the interactions was further investigated by comparing meiofaunal density in the Inclusion treatment (with both physical and trophic effects present) with that in the Disabled treatment (with physical but no trophic effect present). Removal of trophic effect by ‘disabling’ the crab increased meiofaunal density by 30% compared to that in the Inclusion treatment, but at a similar density to the Exclusion treatment. This pattern suggests that the top-down control by soldier crabs on the meiofauna is fundamentally trophic, i.e. predation. In the experiment with fiddler crabs, meiofaunal densities in the inclusion treatments (Inclusion and Disabled) were not significantly different from each other, but density was reduced by more than 50% in the Exclusion treatment. Fiddler crabs significantly impact the meiofauna through their bioturbation activities such as sediment turnover and burrowing, but their trophic activities did not significantly reduce meiofaunal density. Different crab species at different habitats, therefore, may influence meiofaunal density through different processes on sub-tropical soft shores.

Information transfer in a swarm of soldier crabs

Collective behavior is broadly observed in animal groups such as insect swarm, bird flock, and fish school. Both theoretical studies and field observations have investigated possible underlying principles based on local interaction among individuals in a group without global information via conductors or leaders. Information transferred among individuals would play a key role to understand it. In this study, to investigate how individual in a swarm uses information of its own past behavior or swarm mates' behavior, we analyzed behavior of soldier crabs Mictyris guinotae in terms of local active information storage and local transfer entropy.

BOIDモデルによるカニの集団運動の表現

We attempted to simulate the swarm behavior of ‘soldier crabs’ Mictyris brevidactylus with a modified Boids model. Interesting periodical movement of the real crab population was not reproduced by our current model. Further investigation on the real crabs are required to improvement our simulation model.

Collective behavior of soldier crab swarm in both ring- and round-shaped arenas

In study of collective behavior, though collective foraging behavior against surroundings is one of the most vivid examples about how animal group responses to external environment, relative experiment is rare. In this paper, we show an experiment with respect to collective foraging using a swarm of soldier crabs Mictyris guinotae, which live in the tideland and can form large swarms. We recorded the behaviors of soldier crab swarms with 10, 20, 30, 40 individuals in experimental arenas. Thanks to markers attached to crabs' shells and image-processing software, we obtained time series of individuals' position during 30 min. As a consequence, we found the soldier crabs form densely swarm to some extent in the ring-shaped experimental arena. Moreover, when we calculated the time between direction changes of the swarm, we found that it followed power-law distribution, containing very long moves. Such movement pattern is frequently found in foraging behavior of single animals. Our results, therefore, suggest that collective swarms show a type of foraging behavior as a single group.

Emergent runaway into an avoidance area in a swarm of soldier crabs.

Emergent behavior that arises from a mass effect is one of the most striking aspects of collective animal groups. Investigating such behavior would be important in order to understand how individuals interact with their neighbors. Although there are many experiments that have used collective animals to investigate social learning or conflict between individuals and society such as that between a fish and a school, reports on mass effects are rare. In this study, we show that a swarm of soldier crabs could spontaneously enter a water pool, which are usually avoided, by forming densely populated part of a swarm at the edge of the water pool. Moreover, we show that the observed behavior can be explained by the model of collective behavior based on inherent noise that is individuals’ different velocities in a directed group. Our results suggest that inherent noise, which is widely seen in collective animals, can contribute to formation and/or maintenance of a swarm and that the dense swarm can enter the pool by means of enhanced inherent noise.

Collision-based computing implemented by soldier crab swarms

Collision-based computing schemes are implemented using propagating and interacting localisations. When two or more travelling localisations collide, they may reflect or merge into a new localisation. Presence/absence of a localisation in a specified site of a physical space represents True/False values of Boolean variables. Incoming trajectories symbolise inputs and outgoing trajectories are outputs. Logical gates are implemented by collisions between the localisations. We demonstrate how primitives of the collision-based computing can be implemented using swarms of soldier crabs in laboratory experiments. Soldier crabs, Mictyris guinotae, exhibit coherent collective behaviour on an intertidal flat at a daytime low-tide period. The soldier crabs' swarm often moves as a single entity with definite yet dynamically changing boundary. We utilise swarms of soldier crabs to implement a Boolean logic gate. The gate has two inputs and three outputs. Values of the inputs and outputs are represented by crab swarm size or a proportion of crabs in the input and output channels. We demonstrate that the gate performs logical conjunction and negation.

1A1-B03 ゆらぎ指標に基づいた生物の群行動解析(バイオミメティクス・バイオメカトロニクス(1))

This paper analyses the group behavior of soldier crab. In particular, we adopt method of animal-robot interaction and analyses based on fluctuation index. In the experiment, the mobile object interacts with sixteen soldier crabs. From experiment analyses, it was found that collective behavior of crabs has scale free. And this behavior is not affected by the mobile object.

Preliminary Experiments to Elucidate Maintenance Mechanism of Soldier Crabs'Swarm

Preliminary Experiments to Elucidate Maintenance Mechanism of Soldier Crabs'Swarm

The Effect of Mobile Robot on Group Behavior of Animal

This paper observes the effect of a mobile robot on the group behavior of soldier crabs. The mobile robot interacts with eight soldier crabs. For the experimental analysis, this paper adopts four settings. In the first setting, eight soldier crabs are placed in an experiment area without the presence of the robot. In the second, third, and fourth settings, eight soldier crabs are placed in an experiment area with, respectively, a stationary robot, a continuously moving robot, and an intermittently moving robot. These experimental results are analyzed using a fluctuation index. From analysis, it was found that the fluctuation slope for the fourth experiment alone differs from that for other experiments. This result suggests that the intermittently moving robot influences the group behavior of soldier crabs.

Combining process indices from network analysis with structural population measures to indicate response of estuarine trophodynamics to pulse organic enrichment

Indicators of ecosystem structures and processes are important in estuarine health studies but are rarely assessed simultaneously. Organic enrichment affects the abundance and diversity of meio- and macrofauna, but its impact on food web dynamics is less well known. We used a manipulative field experiment combining stable isotope enrichment with compartmental modelling (WinSAAM) and ecological network analysis (EcoNet) to investigate the impacts of organic enrichment on the food web structure and dynamics of an estuarine sandflat, and to evaluate the combined use of structural and process indicators in estuaries. Organic enrichment was achieved by addition of powdered algae to increase organic content (OC) from 0.8% (background) to 3, 5 and 10%. Six dominant compartments including microphytobenthos, meiofauna and soldier crabs (Mictyris longicarpus) were sampled. Increasing organic content decreased the total abundance of meiofauna and number of meiofaunal taxa. C flow rates and indices reflecting system functioning, however, showed non-linear responses. Carbon flow rates between compartments and the proportion of carbon cycling within the system both decreased from background to enrichment at 3 and 5% OC, but then increased at 10% OC. On these measures the highest OC treatment was most similar to background controls, which could be misinterpreted as a sign of health of highly enriched sites. Additional interpretation of indicators for the 10% treatment showed, however, that the high proportion of internal cycling was a result of a much reduced number of compartments (i.e. some taxa had been lost). The combination of trophodynamic process indices and structural population measures together provided the more comprehensive and robust assessment of the effects of organic loading on estuaries.

1A1-S09 ミナミコメツキガニ集団の「群行動原理」理解のための観測・解析システムの開発(バイオミメティクス・バイオメカトロニクス(1))

This paper is aimed at developing analysis and observation system for understanding principal of group of soldier crabs. Especially, in this paper the mobile robot interacts with sixteen soldier crabs. For the experimental analyses, this paper adopts two settings. In the first setting, there are only sixteen soldier crabs in the field. In the second setting, there are the stopping and moving robot and sixteen soldier crabs in the field. These experimental results are analyzed by image processing using OpenCV. From the analyses of two experiments, group of soldier crabs repeat independent behavior and collective behavior. In addition, both iteration has period of 102s. This result suggests that the behavior of soldier crabs has period and this behavior is robust.

First evidence of drilling predation by Conuber sordidus (Swainson, 1821) (Gastropoda: Naticidae) on soldier crabs (Crustacea: Mictyridae)

Moonsnails (Naticidae) are major predators in marine soft substrates worldwide and are thought to prey almost exclusively on shelled molluscs by drilling predation. However, reports on single individuals of various naticid species showing unusual feed-ing behaviour indicate that naticids possibly also feed on other prey which have an external skeleton. The present study pro-vides the first evidence for size selective feeding of an Australian moonsnail (Conuber sordidus) on crustaceans. C. sordidus preys on soldier crabs (Mictyris longicarpus and Mictyris platycheles) on intertidal sand/muddy tidal flats, representing the first well-documented example of a naticid preying on large non-molluscan invertebrates in addition to shelled molluscs. This indicates that prey choice in C. sordidus is less stereotyped than predicted for naticid species, although the feeding mode docu-mented here is similar to that used to capture their main diet of shelled molluscs. The results strongly support some contested earlier studies that have also indicated that naticids will eat non-molluscan prey with an external skeleton, highlighting a need to re-examine generally accepted models concerning naticid feeding ecology.

Short-term response of estuarine sandflat trophodynamics to pulse anthropogenic physical disturbance: Support for the Intermediate Disturbance Hypothesis

Many anthropogenic activities physically disturb urbanised coastal habitats. The functional response of ecosystems to physical disturbances remains largely unknown due to the lack of suitable quantitative tools for assessing impacts. We conducted a manipulative field experiment to investigate the short-term (i.e. temporally sensitive) response of estuarine sandflat trophodynamics to pulse anthropogenic physical disturbance, using combined chemical tracer ( 13C), compartmental modelling and network analysis techniques. Pulse physical disturbance, as sediment pumping for an infaunal bait species, was applied at two disturbance intensities at the commencement of the experiment, in 0.09 m 2 quadrats. Six compartments and three trophic levels in the estuarine sandflat food web were sampled, including the microphytobenthos, four meiofaunal groups, and soldier crabs ( Mictyris longicarpus). Compared with undisturbed controls, in the low disturbance intensity treatment: 1) carbon flow rates between compartments increased, 2) carbon cycling increased, 3) more carbon was retained in the food web, and 4) system indices reflecting ecosystem functioning and resilience were higher. Low disturbance intensity facilitated carbon transfer between organisms and apparently increased resilience. Conversely, high disturbance intensity reduced carbon flow among compartments and carbon cycling, thus lowering resilience. This is the first study with field data quantifying structural and functional changes of sandflat food webs in response to physical disturbance and showed that both ecosystem structure and processes may support the Intermediate Disturbance Hypothesis. This alternative approach to assessing the immediate functional response of estuarine trophic interactions to physical disturbances allows impact detection not possible using conventional approaches.

1P1-P05 小型移動体の振る舞いが生物集団行動へ及ぼす影響(バイオロボティクス)

This paper observes the effect of behavior of mobile robot on group behavior of soldier crabs. Especially, in this paper the mobile robot interacts with eight soldier crabs. For the experimental analyses, this paper adopts four settings. In the first setting, there are only eight soldier crabs in the field. In the second setting, there are the stationary robot and eight soldier crabs in the field. In the third setting, there are the continuously moving robot and eight soldier crabs in the field. In the fourth setting, there are the stopping and moving robot and eight soldier crabs in the field. These experimental results are analyzed by fluctuation index. From the analyses, only fourth experimental fluctuation slope differs from other experiments. This result suggests that the stopping and moving robot has influence on soldier crabs.

Combining stable isotope enrichment, compartmental modelling and ecological network analysis for quantitative measurement of food web dynamics

Summary1. Quantitative food web analysis is made difficult by the need for simultaneous measurement of multiple carbon (C) flows. C flow rates can potentially be quantified indirectly using conventional methods such as gut contents analysis, but the involvement of many conversion factors and assumptions results in significant errors in the final estimation. Such difficulties have limited quantitative data on food web dynamics, restricting community‐level hypothesis testing.2. We conducted laboratory microcosm and field experiments, using combined enriched stable isotope (13C), compartmental modelling and ecological network analysis (ENA) as a novel approach to quantifying food web dynamics. Feasibility of this approach was demonstrated via the quantification of C flow, backflow and cycling in a subtropical estuarine sandflat food web comprising three trophic levels: microphytobenthos (MPB), three dominant meiofaunal groups (juvenile polychaetes, harpacticoid copepods and nematodes) and soldier crabs (Mictyris longicarpus).3. Enriched sodium bicarbonate (NaH13CO3) was used to trace C flow. The compartmental modelling software WinSAAM quantified C flow by comparing the temporal patterns of producer and consumer 13C enrichment. Network analysis software EcoNet was used to assess food web dynamics by providing system indices that quantified the flows and food web interactions.4. This approach allows concurrent quantitative assessment of food web structure and ecosystem functioning. WinSAAM results showed that C return rate from nematodes to MPB was greater than the other two meiofaunal groups and soldier crabs assimilated more C from nematodes than from the other two meiofaunal groups. System indices from EcoNet suggested that indirect flow contributed more than direct flow in this system. Unique capabilities of this approach in food web studies and assumptions underlying the proposed and conventional food web analytical approaches are discussed.5. Another significant advance of this approach is that it allows sensitive quantification of trophic linkages in a food web without requiring equilibrium to be achieved, thus enabling instantaneous assessment of the relative importance of various C flow pathways. Specific hypotheses about food web dynamics, such as the impact of eutrophication and urbanization, can then be tested quantitatively through manipulative experiments by comparing indices reflecting system behaviour.