Shell Fighting Research Articles

Niche overlap and resource partitioning between two intertidal hermit crab species

The gastropod shell influences important aspects of the hermit crab's life; however, the shells are commonly a limited resource. Therefore, different hermit crab species that coexist in intertidal areas are commonly involved in intraspecific and interspecific competition for shells. We assess if differences in shell preference, exploitation ability, or competition by interference can explain the partitioning of shells between the coexisting species Calcinus californiensis and Clibanarius albidigitus. Clibanarius preferred shells of Nerita funiculata among the six gastropod shells tested, while Calcinus did not establish a hierarchy in shell preference. Therefore, the preference for gastropod shell species does not seem to diminish the competition for shells in the wild. Clibanarius identified and attended to chemical cues signalling potential sites of available shells (chemical cues of dead gastropods); Calcinus did not respond to these cues (competition by exploitation). However, Calcinus was more successful in obtaining a new shell by interspecific shell fighting than Clibanarius. Consequently, the use of better quality shells (intact shells) by Calcinus in the wild can be explained by its greater fighting ability compared with Clibanarius. The bias in shell distributions through dominance by shell fighting, more than by exploitation ability, has also been suggested for other hermit crab species of these genera.

Aggressiveness compensates for low muscle strength and metabolic disadvantages in shell fighting: an outcome of the individual’s past

An individual’s metabolic competence is important when escalating to costly behaviours in agonistic encounters. The use of broken shells in the wild induces hermit crabs to reduce their overall metabolic rate; however, these crabs perform better in size-symmetric encounters than crabs that used intact shells in the wild. Given this surprising finding, we explored whether carrying a broken shell increases the resource holding potential (RHP) of hermit crabs by building up their muscle strength. These shells are very heavy, with an unusable portion due to being broken; however, the crabs have to carry the complete structure. Additionally, we explored whether the use of broken shells induces long-lasting consequences in motivation (aggressiveness). We conducted body size asymmetric contests to decrease the relative effect of aggressiveness by increasing the effect of RHP. We predicted a decrease of the agonistic behaviours of crab that occupied broken shells in the wild (CBS) relative to those that occupied intact shells (CIS). Symmetric and asymmetric contests were conducted in pairs formed of a CBS and a CIS, both forced to abandon them and occupy a Nerita shell. The CBS had lower muscle strength, but fought at higher intensity in symmetric contests than CIS. The differences in body mass decreased the expression of agonistic behaviours of CBS relative to CIS. Prolonged poor conditions following the use of a broken shell seem to increase aggressiveness by affecting the long-term subjective resource value. Our findings highlight the role of the recent past associated with shell used on fighting performance. Hermit crabs commonly fight to exchange their inadequate shell for a new one. Although high metabolic rates favour the fighting ability, crabs that occupied broken shells in the wild have low metabolism and perform better in shell fighting than crabs that used intact shells. Broken shells are heavy and larger due to having an unusable portion, but the crab has to carry the complete structure. We explored whether carrying these shells increases muscle strength and/or the aggressiveness of crabs, which might explain their fighting dynamic. Unexpectedly, crabs with broken shells were found to be weaker than those with intact ones. Instead, the use of a broken shell in the wild enhances individual aggressiveness. The results highlight that a previous history under adverse conditions can increase the likelihood of animals with functional disadvantages acquiring better resources.

Preliminary report on the shell fighting behaviour of Pagurus filholi in two different climate regions in Japan

Preliminary report on the shell fighting behaviour of Pagurus filholi in two different climate regions in Japan

Asymmetric effects of contaminant exposure during asymmetric contests in the hermit crab Pagurus bernhardus

Contaminant exposure is known to alter behaviour in a wide range of contexts, including animal contests. We exposed hermit crabs to sublethal concentrations of copper, a common contaminant in coastal ecosystems. When hermit crabs engage in shell fights over empty gastropod shells they adopt two distinct roles. Attackers initiate the fight and perform bouts of vigorous shell fighting, while defenders remain withdrawn into their shells until the encounter is resolved. This role asymmetry means that the two opponents make different strategic decisions during the contest and we utilized an experimental design that allowed us to assess the effect of copper exposure independently on each role. We found that exposure of attackers to copper reduced the number of fights that were initiated, leading to fewer fights in total where the defender was evicted. Of attackers that did fight, those that were exposed to copper were also less likely to evict the defender, but this effect varied with the size difference between the crabs. During the fight, copper exposure caused attackers to rap less vigorously. When defenders were exposed to copper, however, this had no effect on the defender's chance of resisting eviction. Thus, we show for the first time that exposure to a contaminant can alter the outcome of asymmetric contests via differential effects on each of the two roles.

Signal residuals during shell fighting in hermit crabs: can costly signals be used deceptively?

Animals advertise aspects of individual quality in a range of situations including during agonistic contests over access to resources. The advertisement can be produced by different types of signal, which can be broadly classified into ‘‘conventional signals’’ and ‘‘costly signals.’’ In both cases, the signals are thought to be honest such that any benefits to cheating are very limited due to prohibitive costs of advertising an inaccurately high level of quality. However, some individuals may benefit by low-level cheating in systems that are otherwise honest. Here, I test this possibility for a costly signal by analyzing residuals from relationships between a key parameter of signal magnitude and two measures of fighting ability from ‘‘shell fights’’ in hermit crabs. Contrary to the expectations for significant use of bluffing, individuals that performed at a greater magnitude than expected for their ability were more likely to win the encounter but used fewer repetitions than those that performed below the level expected for their ability. This indicates that the level of performance is primarily driven by the cost and that the functional significance of signal residuals in this case is that they provide information on several measures of fighting ability. Key words: contest, cost, deception, hermit crab, honesty, signal. [Behav Ecol]

Resource partitioning and competition for shells in a subtidal hermit crab species assemblage.

Shell and habitat utilization are quantified for 12 hermit crab species occurring subtidally in the San Juan Archipelago, Washington. The mechanism of competition for shells between these species is investigated using laboratory experiments to determine shell preferences, shell acquisition rates, and rates of exchange of shells via shell fighting. This information is used to estimate relative intensities of inter- and intra-specific competition for shells between the species in this assemblage. In contrast to earlier findings on intertidal hermit crab assemblages, a significant number (5) of the species in this assemblage appear to experience a greater reduction in their shell supply due to members of other species than due to other members of their own species. The relative amounts of inter- and intra-specific competition differ greatly for different species in the community. The high average figures for interspecific/intraspecific competition are largely a result of the presence of three abundant and very generalized species. In spite of the large number of species and relatively high ratios of interspecific to intraspecific competition, the species in this group are not close to a limiting similarity in resource use. There is suggestive evidence that greater selection pressures for divergence in habitat use may have resulted in the lower amounts of overlap observed in intertidal hermit crab assemblages in previous studies.

Behavioral Patterns And Derived Hierarchy In Shell Fighting Among Hermit Crabs Pagurus Samuelis (Stimpson, 1857)

Behavioral Patterns And Derived Hierarchy In Shell Fighting Among Hermit Crabs Pagurus Samuelis (Stimpson, 1857)

Shell Wars: Assessment Strategies and the Timing of Decisions in Hermit Crab Shell Fights

The shell fighting behaviour of the hermit crab Pagurus bernhardus was observed under experimental conditions. The relative sizes of the crabs and shell quality of the larger crab influenced the probability of occurrence of a shell fight. These two factors along with the quality of the smaller crab's shell influenced the probability of an escalated fight occurring. During a shell fight, the attacker was able to assimilate information concerning the defender's shell and to compare it with the shell in possession. On the basis of this comparison the attacker decided whether or not to evict the defender and effect a shell change. The time that the attacker took in assessment of the opponent's shell was influenced by a) the quality of the attacker's own shell and b) the ease of discrimination between the qualities of the two shells. Thus decisions were easier in some instances than in others. The defending crab did not have access to information about the attacker's shell and therefore could only estimate the quality of its own shell. This asymmetry of information experienced by the crabs ensured that the attacker decided the outcome of a shell fight.

Frequencies of interspecific shell exchanges between hermit crabs

Frequencies of interspecific shell exchange due to shell fighting were determined for a number of species pairs of hermit crabs from several different locations. Frequencies were determined in the laboratory using a standardized experimental design. Results suggest that most individuals of most species are able to retain adequate or good quality shells in the presence of members of another species occupying poor quality shells. High frequencies of shell exchange always seem to be associated with very asymmetric relationships in which one member of the species pair is clearly dominant over the other. Dominant species usually attain larger sizes than subordinates, are found lower in the intertidal habitat, and are less abundant.

Negotiation or aggression during shell fights of the hermit crab Pagurus bernhardus?

Shell fighting behaviour of the hermit crab Pagurus bernhardus was investigated. Analysis of fights between crabs in which there was little or no asymmetry in potential benefit for the two crabs from a shell exchange suggested that the duration of the fight increased as the potential benefit increased. Further experiments indicated that a naked crab was capable of evicting a housed crab by a process of direct aggression. Analysis of fights in which there was a slight asymmetry in potential gains from shell exchange indicated that the result of the fight was primarily determined by the large of the two crabs. These results are contrary to the proposal of Hazlett (1978) that the interactions represent a process of negotiation rather than aggression.

Shell fighting and competition between two hermit crab species in Panama.

This article is a study of shell fighting between two intertidal hermit crab species in Panama. Laboratory results showed some cases of high exchange frequencies between Calcinus obscurus and Clibanarius albidigitus when the former occupied poor-quality shells. Exchange frequencies varied considerably between collecting sites, and were always low when the defending Clibanarius came from Venado Beach. Shell exchange frequencies estimated from field experiments were similar to those obtained in the laboratory. Observations on relative shell sizes occupied by both species in areas of sympatry and allopatry failed to provide clear evidence that Calcinus reduced the shell size of Clibanarius or that Clibanarius increased the shell size occupied by Calcinus. Results obtained here differ from those obtained in previous studies (Abrams 1980; Bertness 1981a, b), and these differences are discussed. Although shell fighting may be an important component of the interaction of these species, it is likely that roughly 90% of the competition experienced by each species is intraspecific.

AN ANALYSIS OF SHELL OCCUPATION BY TWO SYMPATRIC SPECIES OF HERMIT CRAB. I. ECOLOGICAL FACTORS.

Three series of experiments were conducted on Pagurus longicarpus and Clibanarius vittatus at Beaufort, North Carolina. The first series showed that the preferred species of shell by either species of crab is determined by the size of the crab and that certain species of shells are not available in preferred numbers for the hermit crab species. This affects C. vittatus more than P. longicarpus. The second series showed that shell fighting is not an important factor in determining which species occupies which kind of shell while the third series showed that a substrate preference for mud by P. longicarpus may limit it from obtaining a preferred species of shell that occurs naturally on sand.

The Role of Shell Adequacy in Behavioral Interactions Involving Hermit Crabs

Field studies have suggested that the intertidal hermit crabs of the San Juan Islands of Washington normally occupy snail shells smaller than preferred. In this study the effects of shell size on protection from predation and on hermit crab shell fighting were studied in the laboratory. A predator (Cancer) presented with two hermit crabs (Pagurus granosimanus), identical except in size of occupied shell, preyed upon the hermit in the smaller shell first in 15 out of 16 trials. This results suggests that large shell size confers a selective advantage on the occupying crab. Shell fights involving two hermit crabs (P. hirsutiusculus) of unequal size were observed in which replicates differed only in the shell size of the larger crab. The probability of the larger crab effecting a shell exchange through fighting was shown to increase as the size of its shell decreased. However, shell size was shown to have no effect on the level of aggressiveness as measured by four criteria. The mechanism underlying the former result thus appears to involve a continual high level of general aggressiveness together with an increased tendency associated with occupancy of an inadequate shell by the dominant crab for that crab to evoke a shell exchange during an aggressive interaction.

Tactile Stimuli in the Social Behavior of Pagurus Bernhard Us (Decapoda, Paguridae)

A series of social behavior patterns of the hermit crab Pagurus bernhardus were examined to determine the adequate stimuli for the acts. (1) Cheliped flicking, a rapid out-in movement of one or both cheliped mani, is elicited by touch on any part of the appendages exposed when a crab withdraws into its shell. Execution of flicks is inhibited both by general photic input and by a specific type of visual input (sight of a very large crab) just before ducking in its shell. (2) Dislodging-shaking, a rapid movement up and down of the whole body-shell, is elicited by placement of weight almost anywhere on the back of a crab's gastropod shell. The adequate weight is larger for larger crabs and larger for a given size crab in a heavier shell. (3) Shell fighting behavior is likely when a crab is in a shell that is either too small (in volume) or too large (in weight). Recently moulted crabs more readily lose shell fights and smaller crabs almost never win shell fights against larger crabs. (4) Male P. bernhardus can be sexually excited by contact with the exoskeleton of recently courted females. The stimulus may be chemo-tactic in nature.

Interspecific shell fighting betweenPagurus bernhardusandPagurus cuanensis(Decapoda, Paguridea)

Abstract Observations were made on shell fighting behavior in two species of hermit crabs, Pagurus bernhardus (L.) and Pagurus cuanensis (Bell). Both showed strong preferences for intra-specific fights when brought in from the field, but this preference was no longer present in P. cuanensis when all animals were placed in the same kind of gastropod shell.

Observations on the Social Behavior of the Land Hermit Crab, Coenobita Clypeatus (Herbst)

The social interactions of Coenobita clypeatus resemble those of marine hermit crabs in many ways. Stereotyped movements of the chelipeds and ambulatory legs were often executed as two crabs approached each other. Idividuals also have a repertoire of shell fighting behavior patterns, including rotating movements by the attacker and production of a chirping sound by the defender.