Information transfer during shell exchange in the hermit crab Clibanarius antillensis

The shell exchange behaviour of the hermit crab Clibanarius antillensis was examined for evidence that the non-initiating crab used information about the initiator's shell. Manipulation of the internal volume of the initiator's shell altered the outcome of exchanges in a manner consistent with the negotiations model of resource exchange. It is suggested that the fundamental frequency of shells is detected by crabs during rapping behaviour when the initiator raps its shell against that of the non-initiator.     

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 fights in the hermit crabPagurus geminus: Effect of cheliped use and shell rapping

In shell fights of the hermit crab,Pagurus geminus, frequently it is observed that large crabs (attackers) grasp the thoracic appendage of small crabs (defenders) with the major cheliped and pull the smaller crabs out of their shells. If this is a standard occurrence and result, then the interaction should not be called a “negotiation” (Hazlett 1978). The role of cheliped use by the attckers in the eviction of defenders was therefore studied using crabs with tubes on their chelipeds, and the effect of shell rapping, which is thought to be necessary for eviction, was studied using crabs without shells. The experimental crabs evicted the defenders but fighting was significantly prolonged. Therefore, the negotiation model cannot be rejected. Specific aspects of shell fights in hermit crabs are discussed.     

The power of shell rapping influences rates of eviction in hermit crabs

Hermit crabs fight for ownership of shells, and shell exchangemay occur after a period of shell rapping, involving the initiatingor attacking crab bringing its shell rapidly and repeatedlyinto contact with the shell of the noninitiator or defender,in a series of bouts. The temporal pattern of rapping containsinformation about the motivation and/or relative resource holdingpotential (RHP) of the initiator and acts as a repeated signalof stamina. Here we investigated the role of the force withwhich the rapping is performed and how this is related to thetemporal pattern of rapping by rubberizing the external surfaceof shells. Initiators that are prevented from rapping withtheir usual level of force persist with the activity for longer over the whole encounter but use fewer raps per bout and areless likely to effect an exchange than those supplied withcontrol shells. The fact that the force of rapping affectsthe likelihood of a crab being victorious suggests that eitherthe force of rapping contains information about motivation orRHP or that force directly affects noninitiators, reducingtheir ability to maintain an adequate grip on their shells.The data suggest that shell rapping is an agonistic signalrather than one that provides information useful to the noninitiator,as has been suggested by the negotiation model of shell exchange.     

Shell fights in the hermit crabPagurus geminus: Aggressive act with mutual gain

The shell exchange of the hermit crabPagurus geminus was investigated to see whether it is based on negotiation (Hazlett 1978) or aggression (Elwood & Glass 1981) between the 2 interactants. Two conditions were adopted: the mutualistic condition in which both participants gain from resulting shell exchange, and the competitive condition in which one interactant gains at the expense of the other. The assumption is that if the interactants negotiate, then a higher, and/or quicker, rate of shell exchanges occurs in the mutualistic condition than in the competitive condition. Almost all the defenders (smaller crabs) were evicted from their shells in both of the conditions. No significant difference was detected in the fight time between the conditions, suggesting a low probability of negotiation. In the second experiment, the attackers (larger crabs) were deprived of the use of their chelipeds, allowing me to observe defenders' behavior when they were not subjected to forced eviction. In this case, the defenders evacuated their shells significantly more quickly under competitive conditions, but remained in the shell much longer under the mutualistic condition, indicating that the shell exchange of this species involves no negotiation. The function of shell rapping and the possibilitics of mutual gain in the aggressive interaction are discussed.     

Intraspecific competition and aggression for shells in the hermit crab Pagurus samuel1s

Many studies have investigated shell‐related behaviour in hermit crabs. Few studies, however, have focused specifically on the intraspecies aggression associated with shell competition. We examined intraspecies aggression in hermit crab (Pagurus samuelis) pairs as it relates to competition for a limiting resource, gastropod shells. Pairs of hermit crabs were observed in the laboratory in four different treatments that varied the presence or absence of shells for one or both of the crabs. Measurements of the latency to respond, the number of bouts, and the fight durations were recorded. There was a significant difference among treatments for all three measurements, and naked hermit crabs were much more aggressive than housed hermit crabs. There was no significant difference in aggression between males and females in any of the three treatments. The heightened aggression observed in naked P. samuelis is likely in service of acquiring a protective shell.     

Analysis of the finescale timing of repeated signals: does shell rapping in hermit crabs signal stamina?

Hermit crabs, Pagurus bernhardus, sometimes exchange shells after a period of shell rapping, when the initiating or attacking crab brings its shell rapidly and repeatedly into contact with the shell of the noninitiator or defender in a series of bouts. Bouts are separated by pauses, and raps within bouts are separated by very short periods called 'gaps'. Since within-contest variation is missed when signals are studied by averaging performance rates over entire contests, we analysed the fine within-bout structure of this repeated, aggressive signal. We found that the pattern is consistent with high levels of fatigue in initiators. The duration of the gaps between individual raps increased both within bouts and from bout to bout, and we conclude that this activity is costly to perform. Furthermore, long pauses between bouts is correlated with increased vigour of rapping in the subsequent bout, which suggests that the pause allows for recovery from fatigue induced by rapping. These between-bout pauses may be assessed by noninitiators and provide a signal of stamina. Copyright 2000 The Association for the Study of Animal Behaviour.     

Land hermit crabs use odors of dead conspecifics to locate shells

A series of experiments at two tropical locations tested the ability of land hermit crabs Coenobita perlatus (H. Milne Edwards) and Coenobita compressas (H. Milne Edwards) to detect and respond to odors of dead conspecifics. An attraction array compared numbers of crabs attending hidden food odors and dead conspecific odors. Pit experiments tested crab shell-acquisition behaviors at different hidden odors. Bucket experiments confined crabs collected from various categories (feeding crabs, wandering crabs and crabs aggregated at dead conspecific odors) and tested behavioral responses to odors and an empty shell. Land hermit crab behavior at both sites was similar. Crabs were attracted to dead conspecific odors up to 10 times more than to food odors. Crabs attracted to dead conspecifics displayed significantly more shell-acquisition behaviors: touching other crab's shells in an exploratory manner and switching shells if an empty shell was available. In buckets, crabs from each category switched into shells. Results are compared to previous reports of similar shell-seeking behaviors by marine hermit crabs in response to dead conspecific odors. It is suggested that responding to dead conspecific odors for shell source location is an evolutionarily conserved behavior developed before hermit crabs became terrestrial.     

Shell fights in the hermit crabPagurus geminus: Computer simulation and experiment

The shell exchange in the hermit crabPagurus gemiuns was examined by computer simulations and experiments, to learn whether it is based on mutualistic interactions with both participants gaining, or on one-sided interactions with the large crab gaining regardless of loss and gain of the partner. The result of the experiment showed a much better fit to that of the one-sided simulation than the mutualistic simulation, suggesting that competitive interactions in which small crabs lose in the resulting shell exchanges are a part of shell fights of this species. While the shell exchange attempt can be regarded as aggressive, a higher probability of mutualistic encounters and of successful mutualistic shell exchanges in hermit crabs is discussed.     

New shell acquisition in the hermit crab,Pagurus geminus

The process of how the hermit crab,Pagurus geminus, acquires a new shell was investigated in the natural habitat at Ezura in Shirahama, Wakayama Prefecture, during the non-breeding season, and the following results were obtained. Hermit crabs acquired new shells most frequently by shell exchange between 2 individuals and occasionally by attacking snails. Acquisition through location of empty shells was not found. At the snail attacking site or the site of shell exchange attempts, sometimes many other individuals appeared and, frequently, confusing or complex shell changes were observed. The importance of introduction of fresh shells to a hermit crab population and the possibility for a certain individual to acquire a shell introduced by others through shell exchange attempts are discussed.     

Antipredator defence of the hermit crab Pagurus filholi induced by predatory crabs

Hermit crabs have two antipredator tactics: taking refuge in its shell and fleeing. We examined the following two hypotheses using the hermit crab Pagurus filholi : (1) hermit crabs change their preference for shell types that they take refuge in and/or change the timing of fleeing (i.e. the duration of refuge in the shell) when they perceive a predator threat; (2) the type of shell that a hermit crab occupies affects the fleeing tactic of the individual. Under the stimulus of a crushed conspecific, hermit crabs changed neither their preference for shell species nor their refuge duration. On the other hand, under the stimulus of the predatory crab Gaetice depressus , hermit crabs increased their preference for Batillaria cumingi shells, which provide superior protection against predators, and shortened their refuge duration in the shells even when they occupied those effective against predation. Refuge duration was longer in B. cumingi shells than in the more vulnerable shells of Homalopoma sangarense . These results suggest that both antipredator defences (changing shell and timing of fleeing) are induced by the stimulus of a predator, and the timing of fleeing is affected by the shell type occupied.     

Response of hermit crabs to sinistral shells

Shell rotating behavior of the hermit crabPagurus geminus was investigated. In preliminary observations, hermit crabs motivated to change shells rotated presented shells, filled with sand, in a way that dislodged the inside material. In order to determine if this behavior is stereotyped, or flexible and dependent on shell type, hermit crabs were tested with ordinary dextral shells ofLatirulus nagasakiensis and sinistral shells ofAntiplanes contraria. Sinistral shells are not normally encountered by hermit crabs. Their rotation of the dextral shell to the left was adequate for sand discharge. Sinistral shells were rotated in both directions. Analysis of recorded videotapes showed that variation in rotation direction could be attributed to variation in the position of the crab relative to the shell. When the crab faced the shell aperture from the inner lip, it rotated the sinistral shell to the right, and to opposite direction when it faced from the outer lip side. The crab always pushed the upper side of the horizontally laid shell, regardless of shell type or its own position.     

Symbiosis of sea anemones and hermit crabs: different resource utilization patterns in the Aegean Sea

The small-scale distribution and resource utilization patterns of hermit crabs living in symbiosis with sea anemones were investigated in the Aegean Sea. Four hermit crab species, occupying shells of nine gastropod species, were found in symbiosis with the sea anemone Calliactis parasitica. Shell resource utilization patterns varied among hermit crabs, with Dardanus species utilizing a wide variety of shells. The size structure of hermit crab populations also affected shell resource utilization, with small-sized individuals inhabiting a larger variety of shells. Sea anemone utilization patterns varied both among hermit crab species and among residence shells, with larger crabs and shells hosting an increased abundance and biomass of C. parasitica. The examined biometric relationships suggested that small-sized crabs carry, proportionally to their weight, heavier shells and increased anemone biomass than larger ones. Exceptions to the above patterns are related either to local resource availability or to other environmental factors.     

Shell preference and utilization patterns in littoral hermit crabs of the bay of Panama

Shell utilization patterns of three sympatric hermit crab species from the Bay of Panama are examined. Shell preferences, as shown by laboratory choice experiments and the selective use of empty shells experimentally added to hermit crab populations, are shown to be important determinants of shell utilization under natural conditions.Factors which influence the types and sizes of shells occupied by hermit crabs in separate populations include: (1) the presence and relative abundance of different gastropod species; (2) the specific shell preferences of different hermit crab species; and (3) the presence and relative abundance of sympatric hermit crab competitors for the limited supply of empty shells. Since the size and type of shell occupied by a hermit crab influences its growth rate and reproductive output, these factors appear to have a direct effect on hermit crab fitness and the demographic structure of separate hermit crab populations.     

Interference and exploitation components in interespecific competition between sympatric intertidal hermit crabs

This study was designed to evaluate the effect of interference and exploitation competition in shell partitioning between two hermit crab species (Pagurus criniticornis and Clibanarius antillensis). Field samples revealed that shells of the gastropod Cerithium atratum were the main resource used by both hermit crab species and that Pagurus used eroded or damaged shells in higher frequency than Clibanarius. The exploitative ability of each species was compared between species in the laboratory using dead gastropod (Cerithium) baits to simulate predation events and signalize newly available shells to hermit crabs. Pagurus reached the baits more rapidly than Clibanarius, but this higher exploitative ability did not explain shell utilization patterns in nature. Another experiment evaluated the dominance hierarchy between these two hermit crab species and revealed that Clibanarius was able to outcompete Pagurus for higher quality shells in agonistic encounters. This higher interference competitive ability of Clibanarius in relation to Pagurus may explain field observations. Nevertheless, Pagurus may be responsible to enhance shell availability to other hermit crab species that have lower ability to find and use newly available shells. Differently, the poorer condition of shells used by Pagurus, the higher ability of this species to attend gastropod predation events and its higher consumption rate by shell-breaking crabs (Menippe nodifrons) may increase its predation risks, thus revealing the disadvantages of such an exploitative competitive strategy for hermit crabs.     

Flexing the abdominals: do bigger muscles make better fighters?

Animal contests often involve the use of repeated signals, which are assumed to advertise stamina, and hence fighting ability. While an individual may be predicted to give up once it has crossed an energetic threshold, costs inflicted by its opponent may also contribute to the giving-up decision. Therefore, physical strength should be of key importance in contests, allowing high signal magnitude as well as potentially inflicting costs. We investigated this using hermit crab shell fights, which employ a 'hybrid signal' of shell rapping, which advertises stamina but also imposes potentially deleterious consequences for the receiver. We examined the links between contest outcomes and two proxies for strength; the protein content and relative mass of hermit crab abdominal muscles, the main muscle group used in shell rapping. Our results indicate that there was no difference in muscle protein between winners and losers, whereas winners had significantly greater muscle mass : body mass ratios. Thus, while stamina has been assumed by theory to be an important determinant of agonistic success, the present results demonstrate the importance of muscle size and thereby strength.     

Vacancy Chains Provide Aggregate Benefits To Coenobita clypeatus Hermit Crabs

Vacancy chain theory describes a unique mechanism for the sequential distribution of animal resources across multiple individuals. This theory applies to any resources, such as shelters or nest sites, that are discrete, reusable, and limited in use to single individuals or groups at one time. Hermit crabs rely on gastropod shells for shelter, and a single vacant shell can initiate a chain of sequential shell switches that distributes new resources across many individuals. Using the terrestrial hermit crab Coenobita clypeatus , we examined the previously untested theoretical prediction that this process will yield trickle-down resource benefits to vacancy chain participants (aggregate benefits). In laboratory experiments, we measured improvements in shell quality when a single vacant shell was provided to groups of eight crabs. We found that crabs participating in vacancy chains (averaging 3.2 individuals) gained significant reductions in their shell crowding. In addition, vacancy chains terminated early when experimental groups included a single crab occupying a damaged shell, because damaged vacancies always remained unoccupied. Hermit crabs in damaged shells were more likely to win resource contests for high quality shells against size-matched hermit crabs in crowded shells. Finally, field additions of many new shells to an island population of C. clypeatus hermit crabs reduced average shell crowding for crabs of all sizes, possibly from propagation of benefits through vacancy chains. These results provide empirical support for the theoretical prediction that vacancy chains should provide benefits distributed across many vacancy chain participants. Since shelter-based vacancy chains likely occur in other animals, additional studies of vacancy chain processes should provide new insights into resource acquisition behaviors in diverse animal groups.     

Hermit to king, or hermit to all: multiple transitions to crab-like forms from hermit crab ancestors

The Anomura presents the greatest degree of morphological disparity in the decapod Crustacea, with body forms ranging from the symmetrical and asymmetrical hermit crabs to squat lobsters and king crabs. The phylogeny of the anomurans has been fraught with controversy. Recent debate has focused primarily on the phenomenon of carcinization, the evolution of crab-like form from a non-crab-like ancestor, focused chiefly on derivation of king crabs from asymmetrical hermit crabs--the "hermit to king" hypothesis. We show by phylogenetic analysis of five nuclear protein-coding gene sequences that hermit crabs have a single origin, but surprisingly, that almost all other major clades and body forms within the Anomura, are derived from within the hermit crabs. The crab-like form and squat lobster form have each evolved at least twice from separate symmetrical hermit crab ancestors. In each case, a carcinization trend can be posited via a transition series from the initial symmetrical long-tailed hermit crab form, through the intermediate squat lobster or asymmetrical hermit crab form, to the final crab-like form. Adaptation to dextral shell habitation evolved at least twice, once in an exclusively deep-water clade and once in the common ancestor of all other asymmetrical hermit crabs (from which king crabs are derived). These remarkable cases of parallelism suggest considerable phenotypic flexibility within the hermit crab ground plan, with a general tendency toward carcinization. Rather than having a separate origin from other major clades, hermit crabs have given rise to most other major anomuran body types.     

Gastropod shells: A dynamic resource that helps shape benthic community structure

Empty gastropod shells are an important resource for many animals in shallow benthic marine communities. Shells provide shelter for hermit crabs, octopuses, and fishes, provide attachment substratum for hermit crab symbionts, and directly or indirectly modify hermit crab predation. Creation of an empty shell due to predation of one gastropod on another and acquisition of that shell by a hermit crab are two key events in the subsequent use of that shell. Shells of different gastropod species and the species of hermit crab acquiring them affect the symbiont complement that attaches to the shell, which in turn may affect future shell use by other symbionts. Certain shell types worn by the hermit crab, Pagurus pollicaris Say, are positively associated with the symbiotic sea anemone, Calliactis tricolor (Lesueur), which protects the hermit crab from predation by the crab, Calappa flammea (Herbst), and possibly from the octopus, Octopus joubini Robson. Shells of other species of gastropods are resistant to being crushed by the spiny lobster, Panulirusargus (Latreille). The inter-and intraspecific interactions centered on the gastropod shell are termed a “habitat web.” The potential of the shell to limit the size and distribution of animal populations demonstrates how this resource helps shape community structure.     

Evolutionary palaeoecology of symbioses between bryozoans and hermit crabs

Modern hermit crabs form associations with many organisms which encrust, bore into, or cohabit the living chambers of gastropod shells occupied by the crabs. Among these hermit crab symbionts are bryozoan species which develop massive, commonly multilayered, colonies encrusting hermit crab shells. These colonies extend the living chamber of the crab through a characteristic process of helicospiral tubular growth originating from the shell aperture. The scant information available on the ecology of Recent bryozoan‐hermit crab symbioses is reviewed. Symbioses have been recorded from intertidal to upper slope environments, and from tropical to cold temperate zones. None of the hermit crab species are obligatory symbionts of bryozoans, and the majority of the modern bryozoan species involved are also not obligatory symbionts. Fossil examples always lack the hermit crabs, which have a poor fossilization potential; however, the distinctive tubular growth pattern and other features of the bryozoans enable recognition of ancient examples of the symbiosis. The earliest inferred associations between bryozoans and hermit crabs date from the Mid Jurassic, but associations remained uncommon until the Neogene. A remarkably wide taxonomic diversity of Recent and fossil bryozoans are known or inferred symbionts of hermit crabs. The broad evolutionary pattern of the association demonstrates multiple originations of the symbiosis by bryozoans belonging to at least 5 cyclostome and 12 cheilostome families. Only the Miocene‐Recent cheilostome family Hippoporidridae has an evolutionary history closely tied to symbiosis with hermit crabs. There is no evidence for coevolution.