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.     

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.     

Interspecific competition and coexistence between ants and land hermit crabs on small Bahamian islands

Numerous studies have demonstrated the existence of intra- and interspecific competition among ants, but few have investigated direct competitive interactions between ants and other taxa. In this paper, I present the first evidence of direct competitive interactions between ants and crabs. Evidence of competition for food between ants and the land hermit crab, Coenobita clypeatus (Herbst), was derived from observations and experiments in an archipelago of small islands in the central Exumas, Bahamas. Correlational evidence of competition for food based on occurrences at baits was found between ants and hermit crabs in multiple years. Observations at baits over time revealed species turnover occurred due to aggressive interactions. C. clypeatus discovered food items rapidly, but lost control of food over time, particularly to the ant Brachymyrmex obscurior Forel, which took longer to find food items but recruited large numbers of workers that drove off hermit crabs. A second ant species, Dorymyrmex pyramicus Roger, discovered baits quickly but did not recruit to baits in large numbers, and was not a superior competitor to either C. clypeatus or B. obscurior. Competition between ants and land hermit crabs was not intense enough to cause complementary distributions, and mechanisms of coexistence apparently include temporal variation in foraging activity and complementary foraging strategies when ants and crabs are active at the same time. Because of the widespread distributions and generalist scavenger diets of many ants and crabs, such competitive interactions are likely to be a common facet of many tropical and subtropical insular and coastal communities.     

Mechanisms of coexistence and competition between ants and land hermit crabs in a Bahamian archipelago

Ants and land crabs are common inhabitants of many coastal and insular communities across the tropics and subtropics, and yet direct evidence of interspecific competition between ants and land crabs has only recently been documented. I conducted a series of observational and manipulative experiments to further elucidate the mechanisms of competition, as well as coexistence, in these two groups in an archipelago of small Bahamian islands. Diel baiting trials demonstrated a significant temporal difference in foraging activity between the land hermit crab, Coenobita clypeatus (Herbst), and ant Brachymyrmex obscurior Forel, suggesting this is one mechanism underlying their coexistence on small oceanic islands. Reciprocal manipulative baiting experiments, in which one of a pair of species was removed from baits, documented that aggressive interspecific interactions underlie patterns of complementary distribution and temporal turnover at rich food resources. This was true for competition between hermit crabs and B. obscurior, and between B. obscurior and a second ant species, Dorymyrmex pyramicus Roger. Negative species associations at baits were found to be common throughout an archipelago of 69 small islands. A trade-off in exploitative and interference abilities may be a second mechanism allowing species coexistence on these small islands. Interspecific interactions such as competition and predation may occur commonly between ants and land crabs and have important consequences for the structure and function of tropical and subtropical insular ecosystems.     

Resource partitioning and competition for shells between intertidal hermit crabs on the outer coast of Washington

Summary Resource partitioning was quantified for 6 species of intertidal hermit crabs in the genus Pagurus, that occur on the outer coast of Washington. This, together with field evidence of shell shortage and with laboratory experiments to quantify the mechanism of interactions for shells, allowed estimation of the relative intensities of inter-and intraspecific competition between these species. The findings were that: (1) the magnitude of intraspecific competition was greater than any single interspecific competitive effect for all of the species; and (2) the relative proportion of intraspecific competition was greater for the middle and upper intertidal species than for the lower intertidal species. Studies at several outer coast sites supported these generalizations. Both of these findings are consistent with the hypothesis that competitive divergence has occurred in the past. The structure of the outer coast hermit crab assemblage is compared with that of the San Juan Archipelago hermit crab assemblage. Differences between the two do not seem to be the result of adaptive responses to the presence of more competing species in the former group.     

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.     

Use of energy reserves in fighting hermit crabs

When animals engage in fights they face a series of decisions, which are based on the value of the contested resource and either their relative or their absolute fighting ability. Certain correlates of fighting ability or 'resource holding potential' such as body size are fixed but physiological correlates are expected to vary during the encounter. We examine the role of energy reserves in determining fight outcomes and parameters during 'shell fighting' in hermit crabs. During these fights, the two contestants perform very different roles of attacker and defender. We show that the balance of the total energy pool, in the form of glucose and glycogen, determines the ability of defenders to resist eviction from their shells. Low glucose in evicted defenders is not caused by depletion of energy reserves, rather mobilization of glycogen appears to be the result of a strategic decision about whether to resist effectively, based on the perceived fighting ability of the attacker. Attackers, however, always initiate the fight so such a decision for this role appears unlikely. In addition to influencing decisions and ability during fights, physiological correlates of fighting ability can in turn be influenced by strategic decisions.     

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 fighting and competition between two hermit crab species in Panama

Summary 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.     

Feeding hermit crabs to shrimp broodstock increases their risk of WSSV infection

White spot syndrome virus (WSSV) is a serious shrimp pathogen that has spread globally to all major shrimp farming areas, causing enormous economic losses. Here we investigate the role of hermit crabs in transmitting WSSV to Penaeus monodon brooders used in hatcheries in Vietnam. WSSV-free brooders became PCR-positive for WSSV within 2 to 14 d, and the source of infection was traced to hermit crabs being used as live feed. Challenging hermit crabs with WSSV confirmed their susceptibility to infection, but they remained tolerant to disease even at virus loads equivalent to those causing acute disease in shrimp. As PCR screening also suggests that WSSV infection occurs commonly in hermit crab populations in both Vietnam and Taiwan, their use as live feed for shrimp brooders is not recommended.     

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.     

Effects of shell stress on the growth of hermit crabs

Growth rates of the hermit crabs Pagurus longicarpus Say and P. pollicaris Say maintained in preferred shells and in shells smaller than the preferred size have been compared. Changes in wet weight, shield length, and duration of the molt cycle were determined. Crabs in preferred shells grew significantly faster than those in small shells. P. pollicaris molted at approximately the same rate in both cases but grew more each molt in preferred shells. Von Bertalanffy growth curves were fitted to changes in shield length among crabs in preferred shells. These curves indicate that P. longicarpus may mature four months after settling from the plankton and reach its asymptotic size within the next eight months while P. pollicaris also matures four months after leaving the plankton but does not reach its asymptotic size for approximately three years. The rapid growth of P. longicarpus may enable it to preempt shells which are required for the successful brooding of a large clutch before these shells are required by more aggressive competitors, such as P. pollicaris and Clibanarius vittatus.     

Neuromuscular correlates of rhythmical cheliped flexion behavior in hermit crabs

Journal of Comparative Physiology A -     

How resource quality differentially affects motivation and ability to fight in hermit crabs

Contesting animals typically gather information about the resource value and that information affects fight motivation. However, it is possible that particular resource characteristics alter the ability to fight independently of the motivation. Using hermit crabs, we investigate how the resource in terms of shell quality affects both motivation and ability to fight. These crabs fight for shells, but those shells have to be carried and may impose physiological costs that impede fight vigour. We find that the shell has different effects on motivation and ability. Potential attackers in very small shells were highly motivated to attack but, rather than having enhanced ability, unexpectedly quickly fatigued and subsequently were not more successful in the fights than were crabs in larger shells. We also examined whether defending crabs could gather information about the attacker''s shell from the vigour of the attack. Defending crabs gave up quickly when a potential gain had been assessed, indicating that such information had been gathered. However, there was no indication that this could be owing to the activity of the attacker and the information is probably gathered via visual assessment of the shell.     

Differential tolerance of body fluid dilution in two species of tropical hermit crabs: not due to osmotic/ionic regulation

The tropical intertidal hermit crabs Clibanarius taeniatus and Clibanarius virescens were examined for differences in survival and physiological responses in low salinity. We found that C. taeniatus survived better in dilute seawater than C. virescens and that these species did not differ in their abilities to regulate haemolymph osmolarity, ionic concentration of the haemolymph or body fluid volume. We also found no difference in oxygen consumption between the species when acutely exposed to a range of temperature and salinity combinations. It is concluded that the greater survival in dilute seawater by C. taeniatus compared to C. virescens is due to a greater tolerance of dilution of body fluids by C. taeniatus. Differences in tolerance to dilute seawater may influence the habitat preferences of these species within the same geographical area.     

Effects of chemical context on shell investigation behavior in hermit crabs

Specific chemicals in the environment evoke significant changes in the behavior of many aquatic organisms. We studied in the laboratory whether satiated individuals of the hermit crab, Pagurus longicarpus Say 1817, adjust their investigatory behavior towards an empty, optimal gastropod shell according to differences of chemical context. We also explored to what extent shell investigation by a crab in the same hunger state was affected by occupying an inadequately sized shell. Our results confirmed in part previous findings that crabs can discriminate the odor of freshly dead snails from the odor of freshly dead conspecifics. In the presence of the former odor, crabs inhabiting shells of inadequate size were more responsive and active than those in better-fitting shells. To the contrary, regardless of the quality of the inhabited shell, P. longicarpus remained practically motionless when presented with the odor of freshly dead conspecifics, possibly because the risks of incurring in predators would outweigh the benefits of acquiring a new shell. Unexpectedly, we found that crabs in both types of shell quality exhibited nearly the same behavior in control water, while crabs in adequate shells were more responsive in the presence of food odor. Individuals appeared insensitive to the odor of live snails; indeed, only one hermit crab species has been seen removing living snails from their shells. An intriguing result was that water conditioned by the odors of live conspecifics exerted a strong effect on all the individuals by inducing an intense shell investigation. Our study underlines the central role exerted by chemical detection in hermit crabs' behavior and demonstrates the existence of a complex interplay among chemical context, the physiological state of the animal, and the ecological pressures of the habitat.