Hermit Crab Pagurus Bernhardus Research Articles

Whole-organism performance capacity predicts resource-holding potential in the hermit crab Pagurus bernhardus

Animal contests often involve the production of repeated signals, which are assumed to be energetically demanding to perform and advertise the performer’s fighting ability through a demonstration of stamina. Although the costs of repeated signals have been investigated by the postfight analysis of metabolites, single physiological measures may not adequately reflect an individual’s overall stamina. An alternative approach is to investigate whole-organism performance capacities. We examined the relationship between locomotor capacities and the vigour of repeated bouts of shell-rapping signals during fights over gastropod shells in the hermit crab Pagurus bernhardus . In these fights only attacking crabs perform shell rapping while defenders withdraw into their shell. Successful attackers and defenders had higher mean and maximum walking speeds than losers. Furthermore, maximum speed was a better correlate of fighting ability in defenders, whereas mean speed was better in attackers. This study demonstrates that whole-organism performance capacities correlate with success in agonistic encounters, and that different aspects of performance capacity appear to be important depending on the behaviours performed by different roles. Thus, this study supports the assumptions of theoretical models such as the cumulative assessment model and the energetic war of attrition, which predict that repeated signals advertise stamina and fighting ability, by demonstrating that mean rates of performance, a key component of stamina, are related to success in hermit crab shell fights.

Effects of Predation Threat on the Structure and Benefits from Vacancy Chains in the Hermit Crab Pagurus bernhardus

AbstractVacancy chains occur when individuals occupy discrete re‐useable resource units, which once abandoned by the current owner can then be occupied by a new owner. In order to enter the newly vacated resource the new owner must first vacate its current resource unit, such that a vacancy chain consists of a series of linked moves between resource units of different value, equivalent to different ‘strata’ in the chain. Vacancy chains may represent an important route by which resources are distributed through populations. Indeed, the arrival of a new resource has the potential to initiate a series of moves propagating beyond the individual that encounters the new resource unit. Thus, the chain participants as a whole may experience ‘aggregate benefits’ from the arrival of the new resource unit. The extent of these benefits, however, may not necessarily be evenly distributed between all chain participants; some individuals could receive greater than average benefits by moving through more than one stratum (‘skipping’) and some individuals could experience a reduction in resource value by moving to a resource unit of lower quality than that occupied initially (a ‘backward move’). Such moves represent deviations from the ‘ideal’ vacancy chains assumed by theory. Here we analyse the aggregate benefits and benefits to individuals participating in vacancy chains of empty gastropod shells in the hermit crab Pagurus bernhardus. We also investigate the effect of predation risk on these two levels of benefits and on chain structure. Adding a new shell at the top of the chain causes an overall increase in shell quality after 24 h but the distribution of benefits between strata in the chain varies with the presence and absence of the predator cue. Although there was significant concordance between chain structure in the presence and absence of the predator cue, the structure was significantly different from an ideal vacancy chain in the absence but not the presence of the predator cue.

Hitching a ride on a hermit crabs home: Movement of gastropod shells inhabited by hermit crabs

There is little information on the movement and connectivity patterns for many species. The movement by shells occupied by the hermit crab Pagurus bernhardus and the organisms encrusting these shells was investigated on the south coast of Wales (UK). Hermit crabs shells moved considerable distances along the shore over 1 month periods, moving a minimum mean distance (±SE) of 148 (±8) and 174 (±9) m from release sites in the January and August respectively. Hermit crab-inhabited shells were also found to travel across habitats (sandy areas) that are unsuitable for both hermit crabs and epibionts. Through the examination of 150 of the most abundant shells used by P. bernhardus ( Nucella lapillus), twelve epibiont species were found (10 animal and 2 algal species) and choice experiments demonstrated that hermit crabs preferred epibiont covered shells (84%), compared with bare shells (16%). The distance that shells were moved and the preference of hermit crabs for epibiont encrusted shells, coupled with the ability for epibionts to cross unsuitable habitats, may provide a dispersal advantage for epibiont species.

Aerobic capacity influences giving-up decisions in fighting hermit crabs: does stamina constrain contests?

Strategic decisions in animal contests have been increasingly understood in terms of the physiological consequences of fighting, in particular by investigating energetic costs. In addition to these costs, the scope for vigorous agonistic activity may be modified by the aerobic capacity of individuals, engaged in a fight, which can be linked to circulating levels of respiratory pigment. Greater concentrations of respiratory pigment should increase aerobic capacity, thus enhancing aerobic respiration, postponing the onset of anaerobia, and reducing the amount of metabolic acidosis incurred. We examined postfight levels of the respiratory pigment haemocyanin in the hermit crab Pagurus bernhardus. The concentration of haemocyanin was higher in winners than losers, but was also positively correlated with body size. Residuals calculated for how much each individual deviated from this relationship revealed that individuals that had more positive residuals were more likely to win aggressive encounters. Thus, greater levels of respiratory pigment appear to enhance agonistic performance via their influence on endurance and aerobic capacity.

The Role of Circulating Metal Ions During Shell Fights in the Hermit Crab Pagurus bernhardus

AbstractFighting animals must make a series of decisions, and understanding the proximate causes behind these decisions can give insight into how they are made. For example, fights have been analysed with respect to energetic costs and endocrine changes associated with engaging. However, another mechanism for the control of demanding activity, such as fighting, is the modulation of aerobic capacity by divalent metal ions. Here we examine post‐fight haemolymph concentrations of magnesium (Mg2+) and calcium (Ca2+) ions in the common European hermit crab Pagurus bernhardus. Hermit crabs fight over the ownership of gastropod shells, where they adopt two very different roles during the encounter: attacker and defender. Despite the two roles performing different activities, we found that Mg2+ and Ca2+ affected them similarly, with concentrations of these ions being highest in successful individuals. Haemolymph concentrations of Mg2+ and Ca2+ were also found to increase as a result of fighting, and these elevated levels will, via allosteric interactions, increase the oxygen affinity of the respiratory pigment haemocyanin, enhancing respiratory capacity and therefore fighting ability. Furthermore, the present study revealed that seasonal changes in circulating levels, along with the ability of competitors to respond to them, may ultimately influence an individual’s success in aggressive interactions.

Comparing the strength of behavioural plasticity and consistency across situations: animal personalities in the hermit crab Pagurus bernhardus

Many phenotypic traits show plasticity but behaviour is often considered the 'most plastic' aspect of phenotype as it is likely to show the quickest response to temporal changes in conditions or 'situation'. However, it has also been noted that constraints on sensory acuity, cognitive structure and physiological capacities place limits on behavioural plasticity. Such limits to plasticity may generate consistent differences in behaviour between individuals from the same population. It has recently been suggested that these consistent differences in individual behaviour may be adaptive and the term 'animal personalities' has been used to describe them. In many cases, however, a degree of both behavioural plasticity and relative consistency is probable. To understand the possible functions of animal personalities, it is necessary to determine the relative strength of each tendency and this may be achieved by comparison of statistical effect sizes for tests of difference and concordance. Here, we describe a new statistical framework for making such comparisons and investigate cross-situational plasticity and consistency in the duration of startle responses in the European hermit crab Pagurus bernhardus, in the field and the laboratory. The effect sizes of tests for behavioural consistency were greater than for tests of behavioural plasticity, indicating for the first time the presence of animal personalities in a crustacean model.

New insights into evolution of crustacean hyperglycaemic hormone in decapods – first characterization in Anomura

The neuropeptides of the crustacean hyperglycaemic hormone (CHH) family are encoded by a multigene family and are involved in a wide spectrum of essential functions. In order to characterize CHH family peptides in one of the last groups of decapods not yet investigated, CHH was studied in two anomurans: the hermit crab Pagurus bernhardus and the squat lobster Galathea strigosa. Using RT-PCR and 3' and 5' RACE methods, a preproCHH cDNA was cloned from the major neuroendocrine organs (X-organs) of these two species. Hormone precursors deduced from these cDNAs in P. bernhardus and G. strigosa are composed of signal peptides of 29 and 31 amino acids, respectively, and CHH precursor-related peptides (CPRPs) of 50 and 40 amino acids, respectively, followed by a mature hormone of 72 amino acids. The presence of these predicted CHHs and their related CPRPs was confirmed by performing MALDI-TOF mass spectrometry on sinus glands, the main neurohaemal organs of decapods. These analyses also suggest the presence, in sinus glands of both species, of a peptide related to the moult-inhibiting hormone (MIH), another member of the CHH family. Accordingly, immunostaining of the X-organ/sinus gland complex of P. bernhardus with heterologous anti-CHH and anti-MIH sera showed the presence of distinct cells producing CHH and MIH-like proteins. A phylogenetic analysis of CHHs, including anomuran sequences, based on maximum-likelihood methods, was performed. The phylogenetic position of this taxon, as a sister group to Brachyura, is in agreement with previously reported results, and confirms the utility of CHH as a molecular model for understanding inter-taxa relationships. Finally, the paraphyly of penaeid CHHs and the structural diversity of CPRPs are discussed.

Behavioural colour change in the hermit crab Pagurus bernhardus: reduced crypticity when the threat of predation is high

One means of avoiding detection by predators is to employ cryptic colouration. In some cases, individuals can rapidly adjust their colouration, enabling them to remain cryptic in a heterogeneous environment or to vary colouration in response to predation threat. This is often achieved physiologically but in some cases animals are able to adjust their external appearance by behavioural means. Hermit crabs could potentially enhance their crypticity by occupying gastropod shells that match the substrate. However, changing shells is risky and the benefits of crypsis must be balanced against the imminent threat of predation. Here we show that naked hermit crabs initially enter the shell that shows the greatest contrast with the substrate, but may subsequently move into a shell that offers a greater degree of background matching. However, in the presence of a predator cue they tend to remain in the shell that offers low crypticity. This indicates that rapid colour change may be effected by behavioural mechanisms but this is restricted by the need to make a behavioural decision on the basis of a range of information sources.

Inter-sexual contests in the hermit crab Pagurus bernhardus: females fight harder but males win more encounters

Contests often occur between members of the same sex when they compete for access to mates, but inter-sexual contests may occur over access to other essential resources such as food or shelter. Despite the possibility that such contests are common, most studies focus on male fighting, and very few have analysed fights between males and females. Because males and females differ physically and physiologically, fighting ability or resource-holding potential (RHP) may also be subject to inter-sexual variation. In this study, we investigate size-controlled inter-sexual contests over the ownership of empty gastropod shells in the hermit crab Pagurus bernhardus. During these fights, there are two roles, attacker and defender, and we use a fully orthogonal experimental design to compare the performance of males and females in each role, when fighting either a male or female opponent. Although females fight more intensely, male attackers have an advantage when compared to females playing the attacker role, as they are more likely to evict the defender from its shell and thus win the resource. Further, in the defender role, male defenders are subject to shorter attacks than female defenders. The differences in agonistic performance could not be attributed to differences in perceived resource value between the sexes or to differences in body or weapon size. There are clear differences in the agonistic behaviour of males and females, and this possibility should be incorporated into models of contest behaviour. In particular, evolutionarily stable strategies may be expected to vary with sex ratios.

Monoamines and decision making during contests in the hermit crab Pagurus bernhardus

During fights animals are expected to make a series of strategic decisions that involve interactions between information about the contest and the individual's nervous system that produce a change in behaviour. Biogenic monoamines such as serotonin (‘5-HT’) and dopamine are thought to prime decision-making centres for appropriate responses during aggressive interactions in crustaceans, and circulating levels vary both between individuals and during agonistic encounters. Aminergenic systems operate in diverse animal taxa and in this study we assayed circulating levels of 5-HT and dopamine following shell fights in the common European hermit crab, Pagurus bernhardus. The two roles in these fights, attacker and defender, perform different activities but, in both, 5-HT increased and dopamine declined in response to engaging in a fight. In defenders but not attackers, giving up was correlated with low 5-HT and dopamine. In attackers, motivation to initiate a fight was positively correlated with dopamine levels. Circulating monoamines are therefore involved in decision making during these aggressive encounters.

Use of chemical cues during shell fights in the hermit crab Pagurus bernhardus

AbstractChemical communication is likely to play an important role during agonistic encounters in aquatic crustaceans but the use of chemical signals is difficult to observe. An alternative approach to direct observation is to collect water that has contained fighting animals and then expose a focal animal of the same species to the cue water and monitor its behaviour. Here we investigate the possibility of the use of chemical cues during 'shell fights' in the hermit crab Pagurus bernhardus. Focal crabs exposed to the fighting cue spent more time withdrawn into their gastropod shell, less time on locomotion and less time searching for food than did those exposed to cues from non-fighting hermit crabs or those treated with plain sea water. At the end of the observation period we used a novel stimulus to induce a startle response in order to probe the focal crab's motivational state for this exploratory behaviour. Those exposed to the fighting cue water took longer to recover than crabs in the other groups, indicating that their motivation was lower. These findings provide clear evidence that chemical cues are a feature of these contests.

Taxonomy and distribution of the hydrozoan and protozoan epibionts on Pagurus bernhardus (Linnaeus, 1758) (Crustacea, Decapoda) from Scotland

AbstractProtozoan and hydrozoan epibionts on the hermit crab Pagurus bernhardus and its shell, collected near Cumbrae Island (Scotland) were studied. The epibionts found were the following: (1) protozoans: the suctorian ciliates Ephelota plana, Acineta compressa, Conchacineta constricta, Corynophrya anisostyla; the peritrich ciliates Cothurnia mobiusi and Zoothamnium plumula; the chonotrich ciliate Chilodochona quennerstedti; and (2) hydrozoans: the species Leuckartiara sp. and Clytia sp. The morphological characteristics of the epibionts were analysed, as well as their taxonomic position. The distribution of epibionts on the crab surface and its shell was studied, and the density and biomass of epibionts were calculated on each anatomic unit. There was a differential distribution according to the type of epibiont: hydrozoans dominated in biovolume and were present mainly on the shell, meanwhile protozoans represented the highest fraction of density and they were found exclusively on the crab (principally on eyes, antennulae, antennae, maxillipeds, pereopods and uropods). The anterior area of the cephalothorax was the most colonized. On this area, the maxillipeds and second pereopods showed the highest densities. The location of each epibiont species was described. There was a correlation between the length of the crab and the total number of hydrozoans. There was a significant correlation between the right and the left units of the crab, taking into consideration the mean densities of epibionts on each anatomical unit. The shell was colonized by the same species of hydrozoa that appeared on the crab, although in a much higher density (mean 3024.38 per shell; 6.9 per crab). There was a significant difference between both species of hydrozoan epibionts with respect to the mean densities on the different areas of the shell. The zone of the shell more occupied by Clytia sp. was the apical zone of the shell, while the highest densities of Leuckartiara sp. were registered near the aperture of the shell. The hydrozoan and protozoan epibiont species found on P. bernhardus in this study represent the first mention of their presence on this hermit crab.

Influence of occupant microhabitat on the composition of encrusting communities on gastropod shells

The exploitation of microhabitats is widely considered to increase biodiversity in marine ecosystems. Although intertidal hermit crabs and gastropods may inhabit the same shell type and shore level, their microhabitat may differ depending on the state of the tide. On the south coast of Wales the hermit crab Pagurus bernhardus mainly inhabits the shells of Nucella lapillus (84%). Hermit crab shells had a significantly different encrusting community compared with live N. lapillus shells. At low tide the live gastropods were found on exposed rock surfaces whereas hermit crabs were restricted to tidal pools. Communities encrusting live gastropod shells were characterised by lower species richness and abundance compared with shells inhabited by hermit crabs (12 species found in total). A greater abundance and richness of epibionts was recorded from both shell types during the summer compared with winter. Differences in community composition between shell occupant types were attributed to microhabitats used by gastropods and hermit crabs and the associated desiccation pressures, rather than competitive interactions or shell characteristics. This contradicts earlier studies of subtidal shells where biological processes were considered more important than physical factors in controlling species abundance and richness patterns. The use of rockpool microhabitats by hermit crabs increases the biodiversity of rocky shores, as some species commonly found on hermit-crab-inhabited shells were rare in other local habitats.

Demersal fish and epifauna associated with sandbank habitats

A habitat specific survey of the epifauna and fish fauna of sandbanks off the Welsh coastline was undertaken in 2001. Of these, three sandbanks were considered to represent extensions of shallow nearshore soft-sediment communities, while a further six sandbanks were considered to be distinct sandbanks; seabed features clearly defined in comparison with surrounding sediments. Multivariate community analyses revealed that the distinct sandbanks had both fish and epifaunal assemblages that were distinct from those sandbanks considered to be extensions of nearshore sediments. The distinct sandbanks were typified by low species diversity and shared indicator species such as the weever fish Echiichthys vipera, the shrimp Philocheras trispinosus and the hermit crab Pagurus bernhardus. Differences occurred in species composition among the distinct sandbanks, in particular, southern sandbanks were typified by sand sole Solea lascaris and small-eyed ray Raja microocellata. The sandbanks considered as extensions of nearshore sediments shared many similarities with the Pleuronectes platessa– Limanda limanda assemblage, identified by Ellis et al. (Estuar. Coastal Shelf Sci. 51 (2000) 299), which is widespread in the Irish Sea. Sandbanks, as a habitat definition under the EU habitats directive, are likely to incorporate a number of physically and biologically distinct habitats of which two have been described in the present study.

Motivational change during shell fights in the hermit crab Pagurus bernhardus

During agonistic interactions the motivation of each contestant is expected to vary because of increased information and changes in fighting ability. In shell fights between hermit crabs over gastropod shells, attackers rap their shell in a series of bouts against that of the defender whereas defenders remain withdrawn into their shells until the encounter is resolved; either the defender is evicted from its shell or the attacker ‘gives up’ and the defender retains its shell. We assessed the motivational state of attackers for performing rapping by measuring the duration of startle responses elicited by a novel stimulus. We staged fights between pairs of crabs in six different groups defined by the potential gain in shell quality available to attackers (high or low) and by the point at which the novel stimulus was applied (prior to rapping, after one bout or after four bouts). Startle response duration decreased during the first four bouts of fighting and showed a U-shaped relationship with the relative difference in size between the crabs. There was no difference in startle response duration between high- and low-gain groups. Individuals showing short startle responses were likely to be victorious and we conclude that the relationship between the relative size difference of the opponents and startle duration reflects that between size difference and the cost of gaining an eviction.

Damage sustained by epibenthic invertebrates discarded in the Nephrops fishery of the Clyde Sea area, Scotland

The Clyde Sea Nephrops fishery produces ca. 25 000 t y −1 discards with invertebrates accounting for up to 90% of the number of animals discarded. Trawling and handling of the (by-)catch often results in physical injury, the extent of which was previously unknown. Damage sustained by invertebrate discards was assessed following commercial trawling (of 62–270 min duration) and sorting on deck. Brittlestars Ophiura ophiura were most vulnerable with 100% incurring damage, followed by squat lobsters Munida rugosa (57%) and starfish Astropecten irregularis (56%). Harder-shelled species such as hermit crabs Pagurus bernhardus and queen scallops Aequipecten opercularis sustained fewer injuries (14 and 2%, respectively). Shell chipping, loss and damage of limbs were the most frequent types of injury incurred. The severity and frequency of damage was mainly correlated with species-specific morphological and behavioural characteristics. Vessel type, tow duration and animal size had a major influence on damage to the epibenthic invertebrates caught. While damage may potentially be repaired, survival is adversely affected and sublethal effects might significantly impair fitness of frequently trawled individuals and populations.

Survival of decapod crustaceans discarded in the Nephrops fishery of the Clyde Sea area, Scotland

The Clyde Sea Nephrops fishery produces large amounts of invertebrate discards. Of these, as much as 89% are decapod crustaceans, including the swimming crab Liocarcinus depurator (Linnaeus, 1758), the squat lobster Munida rugosa (Fabricius, 1775) and the hermit crab Pagurus bernhardus (Linnaeus, 1758). The short-term mortality of these species was assessed following trawling and periods of aerial exposure on deck (16–90 min), and ranged from 2–25%, with Pagurus bernhardus showing the lowest mortality. Two experiments were performed to determine the longer-term survival of trawled decapods compared to those with experimentally ablated appendages. Deliberately damaged decapods had a significantly lower longer-term survival (ca. 30%) than controls (72–83%). Survival of trawled Liocarcinus depurator that had been induced to autotomize two appendages was slightly lower (74%) compared with intact creel-caught animals (92%). Mortality rates stabilised about 10 d after trawling. Our results suggest that post-trawling mortality of discarded decapod crustaceans has been underestimated in the past, owing to inadequate monitoring periods.

Less choosy or different preference? Impact of hypoxia on hermit crab shell assessment and selection

Hermit crabs that rely on gastropod shells for protection have to assess a number of shell features, each of which can bring different, and sometimes conflicting, advantages to their bearer. We examined how environmentally induced stress, in the form of hypoxia, can alter the relative benefits of different shell features and result in the selection of different shells by the hermit crabPagurus bernhardus. Hermit crabs under hypoxic conditions spent significantly less time investigating shells before entering them. Despite this apparently superficial assessment, they chose shells that were well suited to hypoxic conditions. After 24h, they were found in shells that were significantly lighter than those chosen by hermit crabs under normal oxygen. This shift in preference was achieved at the expense of the internal spaciousness of the shell, which may have deleterious implications for predation and reproduction. This cost was more evident for larger hermit crabs since there was no relationship between hermit crab size and shell characteristics for hermit crabs in hypoxia. Under oxygen stress, hermit crabs therefore alter their shell preference in favour of lighter, and thus smaller, shells, probably reflecting a greater concern for energy minimization than protection from predation or reproduction.

Analysis of repeated signals during shell fights in the hermit crab Pagurus bernhardus

Shell exchanges between hermit crabs may occur 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 non-initiator or defender, in a series of bouts. There are two opposing models of hermit crab shell exchange and the function of shell rapping. The negotiation model views shell exchange as a mutualistic activity, in which the initiator supplies information about the quality of its shell via the fundamental frequency of the rapping sound. The aggression model views shell rapping as either detrimental to the defending crab, or as providing it with information about the initiator's ability or motivation to continue, or both. The negotiation model makes no predictions about the temporal pattern of rapping, but under the aggression model it would be expected that crabs that rapped more vigorously would be more likely to effect an exchange. Repeating the signal could be expected under either model. Crabs that achieve an exchange rap more vigorously, rapping is more persistent when a clear gain in shell quality may be achieved, and the vigour is greater when the relative resource-holding potential (or 'fighting ability') is high. These findings support the aggression model rather than the negotiation model. Contrary to the predictions of game theory, crabs that do not effect an exchange appear to signal that they are about to give up. The data suggest that rapping is performed repeatedly because the accumulation of all of the performances acts as a signal of stamina.

Responses of benthic scavengers to fishing disturbance by towed gears in different habitats

The aggregation and feeding behaviour of invertebrate scavengers in areas disturbed by trawling was investigated at three different localities. At each site a fishing disturbance was created using a commercial 4 m beam trawl and scavenger density was quantified using a light beam trawl. At one site two diver surveys were also carried out; along a line fished with a scallop dredge or a beam trawl on two separate occasions. For all experiments the fished and adjacent unfished control areas were sampled before, and at intervals after, the initial fishing disturbance. Sampling with the light beam trawl revealed that hermit crabs Pagurus bernhardus moved into areas which had been fished with a 4 m beam trawl at an experimental site near Anglesey. The density of these hermit crabs increased significantly in the fished area after fishing had taken place, but no change in density occurred in the adjacent control (unfished) area. At two other sites (Red Wharf Bay, Anglesey and a site offshore from Walney Island) there were no detectable increases in scavenger numbers in the fished areas. Furthermore, at the site near Walney Island, numbers of hermit crabs P. bernhardus, swimming crabs Liocarcinus depurator and starfish Asterias rubens actually decreased after fishing. Thus the responses of scavengers to towed fishing gears varied considerably between different communities. At Red Wharf Bay, divers observed similar responses of scavengers to both beam trawl and scallop dredge disturbance. Four predatory species were observed feeding in the fished area; starfish A. rubens, hermit crabs P. bernhardus, brittlestars Ophiura ophiura and whelks Buccinum undatum. These predators fed on damaged bivalves, echinoderms, crustaceans, whelks and polychaetes. The proportion of starfish feeding in the fished area was significantly higher after fishing had taken place. Demersal fishing activities provide food for scavengers in the form of damaged animals which are left in the tracks of the trawl or dredge. The responses of scavengers to fishing disturbance are not always manifested as a large increase in their abundance. It is clear that the magnitude of response varies between species and between habitat types.