Effects of shell utilization on reproductive patterns in tropical hermit crabs

Dittoral and sublittoral hermit crabs (Coenobita clypeatus, Clibanarius tricolor, Calcinus dibicen, Petrochirus diogenes, Paguristes grayi, Pagurus miamensis, Paguristes tortugae, Paguristes cadenati and Pagurus sp.) were studied on Lighthouse Atoll, Belize. The Clibanarius tricolor population differed markedly in mean clutch size from congeneric populations at temperate latitudes and from conspecific populations in the Florida Keys. These differences can be attributed primarily to variation in shell utilization pattern, overlap with competitors, and breeding season. Regression analyses indicate that shell weight but not internal shell volume affects the clutch size of C. tricolor in Belize, probably due to selection for optimum volume resulting in the use of broken and encrusted shells with high weight: volume ratios. Both egg size and clutch size differed significantly among egg developmental stages in C. tricolor, Calcinus tibicen, and Pagurus miamensis.     

Richness,abundance and shell use of subarctic and arctic hermit crabs

Hermit crabs are an obvious, common and abundant feature of global shallow water environments but almost nothing is known of their ecology at their extreme latitudinal ranges, the Arctic and southern South America. In this study, we report the first investigation on hermit crabs and their use of a key resource, gastropod shells, in a subpolar and a polar environment—amongst the most rapidly changing places on earth. Hypothesised low levels of richness were confirmed by surveys—only Pagurus pubescens was found in western Spitsbergen and only three pagurids were found in northern Norway. At the northern-most of their extent, hermit crabs were fairly common but Arctic abundances (1–5 m⁻²) were an order of magnitude lower than in many warm temperate or tropical localities. Along the open coast of Spitsbergen, the occurrence of P. pubescens was infrequent and very patchy, but it was more abundant in the fjords. In Isfjorden, the largest studied fjord, the population of P. pubescens was mainly represented by small individuals. Spitsbergen P. pubescens used few shell types and >87% just occurred in Margarites or Buccinum shells. The proportion of the gastropod shells, used by P. pubescens, which were damaged, was high and increased with shell size. These hermit crabs are at the edge of the range for both their species and Anomura. The extremes of their location are reflected by: They probably represent the least rich assemblage, with the lowest and most patchy typical abundances reported to date and are amongst the smallest individuals using the least diverse and most damaged gastropod shells.     

Binary individual recognition in hermit crabs

One mechanism that permits the maintenance of dominance hierarchies is individual recognition, defined as the ability of an animal to recognize a conspecific on the basis of one or more identifying cues, and to associate it with experiences of victories or defeats that the animal has gained from preceding encounters with that particular individual. We examined whether the long-clawed hermit crab, Pagurus longicarpus, could differentiate between unfamiliar and familiar opponents. The experimental protocol was designed to control in pairs of interacting individuals several factors together, such as status and relative size of the opponent, as well as species, quality, and fit of the inhabited shell. The hermit crabs were more reactive and their agonistic level was higher in unfamiliar than in familiar pairs; in addition, betas were more prone to initiate an interaction with unfamiliar than with familiar alphas. The alternative explanation—that the ability to discriminate between familiar and novel shells can explain our results per se— was tested following, in part, Jackson and Elwoods (1989) protocol for Pagurus bernhardus and was, at least for this species, rejected. This study did not determine whether a true individual recognition occurs, but demonstrated that P. longicarpus categorizes the individuals into two heterogeneous subgroups, thus being capable of a binary discrimination among opponents.Communicated by T. Czeschlik     

Temporal and spatial settlement patterns of sympatric hermit crabs and the influence of shell resource availability

Larvae of marine organisms often need specific resources or environments at settlement, and their success at settlement might be strongly influenced by the abundance and distribution of such specific resources. The larvae of hermit crabs need small shells to settle, so it is thought that the distribution and abundance of small shells influence the settlement pattern of hermit crabs. To investigate the influence of small shell distribution on the settlement of pagurid hermit crab larvae, we conducted a field experiment at an intertidal rocky shore in Hakodate Bay, Japan. From the line-transect sampling in the field, we found that Pagurus middendorffii settled extensively in the offshore side of the intertidal zone while P. nigrofascia settled in the uppermost area of the intertidal zone. Small shells were most abundant in a narrow shallow trough, slightly offshore from the uppermost area of the intertidal zone. For both species, settler abundance was high where adults were abundant, but settler abundance did not appear to be related to shells abundance. An experiment to clarify settlement patterns showed that larval recruits tended to be similar to those in the line-transect sampling of settlers. Thus shells may not be a primary factor affecting settlement patterns at relatively large scale within the intertidal flat. However, when we analyzed the relationship of settlers and shells separately within each transect, the distribution of settlers was well explained by shell resource availability. Therefore on a smaller scale, shell availability may influence the number of settlers. Settlement periods of P. middendorffii and P. nigrofascia fully overlapped, so their larvae probably were affected by similar transport factors, such as current and tidal movement. Nevertheless they showed different spatial patterns of settlement.Communicated by T. Ikeda, Hakodate     

Metabolic consequences of shell choice in Pagurus bernhardus: do hermit crabs prefer cryptic or portable shells?

Hermit crabs are unique among crustaceans in that they choose their shell and can, therefore, be used to investigate apparent preferences for the presence of epizoic fauna. These may be beneficial due to increased protection from predators via enhanced crypsis but may also make the shell more difficult to carry. The effects of encrusting fauna on the physical properties of empty gastropod shells, the shell preferences of hermit crabs and the physiological costs of shell carrying were examined in the present laboratory study. Heavily encrusted shells weighed more than shells of the same internal volume that were free of epizoic fauna, hermit crabs showed a clear preference for un-encrusted shells and those that occupied encrusted shells had elevated haemolymph lactate in comparison to those supplied with un-encrusted shells. Under laboratory conditions, any benefit from increased crypsis is, therefore, outbalanced by the increased costs of carrying encrusted shells.     

Communication and mutual resource exchange in north Florida hermit crabs

Summary The patterns of shell exchange in three species of hermit crabs which overlap in distribution and shell use were observed in the laboratory. Crabs showed no tendency to initiate more exchanges with conspecifics as compared with nonconspecific individuals and there were no specific size dominance effects. Lack of common communicatory patterns betweenClibararius vittatus andPagurus pollicaris was correlated with minimal actual exchange, whilePagurus impressus exchanged with both species and executed patterns in common with both. The pattern of shell exchanges and preferences indicated that, in some cases, both individuals may gain in interspecific exchanges.     

Evaluation of hermit crab shell indices

A study on the alimentary ethology of conger eels was carried out over a period of four years. Individuals were captured at a depth ranging from 10 to 800 m. The parameters analysed lead to the following observations: (a) in the Central Mediterranean basin the feeding of Conger conger (L.) populations was mainly based on Osteichthyes, Crustacea and Cephalopoda; (b) the neritic population fed on a higher number of species than the epimesobathyal. The high percentage of empty stomachs in the bathyal population was due to the fact that the neritic females, at the end of trophic phase, set out on a reproductive migration towards the bathyal level.     

Influence of size,species and damage on shell selection by the hermit crabPagurus longicarpus

Shell preferences were examined inPagurus longicarpus Say, collected from Wakulla Beach, Florida, USA in 1987. Relative shell size was a more important shell characteristic in shell selection than either shell species or shell damage. Hermit crabs rarely selected relatively large shells but often selected relatively small shells over damaged shells. Preferences for a particular shell species were offset by varying the relative size or condition of the preferred shell species. Because specific environmental pressures are linked to particular shell characteristics, an assessment of the importance of various shell features may indicate which environmental pressures are ameliorated via the gastropod shell. Predation and desiccation are linked to relatively small shells and particular shell species; these stresses may be minimized by alternative behavioral mechanisms.     

Ecology of subtropical hermit crabs in SW Madagascar: short-range migrations

Many mobile animals migrate because of the different benefits provided by different localities in time and space. For hermit crabs, such benefits include resource (shell, water, food) acquisition and gamete release. One of the more successful crustacean land-invaders, Coenobita hermit crabs, undertake complex short-range migrations in SW Madagascar. Number of active hermit crabs was inversely related to wind strength and positively related to tidal range, emphasising that movement would conserve water. A circadian component was also recorded in the locomotory activity of Coenobita pseudorugosus and C. rugosus. Path linearity varied with many of the same parameters, but also with beach slope. Movement was primarily perpendicular to shore in small individuals, but the parallel proportion increased with hermit crab size and tidal range, probably driven mostly by shell and food searching. Despite the costs of movement and shell carriage in the terrestrial environment, C. pseudorugosus and C. rugosus were as fast as their marine counterparts. Their speeds varied principally with individual size and were approximately 20% faster without shells and about 20% slower when climbing up a 20° slope, compared to horizontal or downhill travel. Hermit crabs, which are highly numerous and speciose in SW Madagascar, do not seem to partition niches by differential movement patterns. Aside from provision of shells in middens and capturing large adults for bait or pets, human activity may have a profound effect on hermit crab movement: observations at rare uninhabited marine reserves like Nosy Ve show that considerable diurnal activity may take place despite the apparent hostility of the environment to an essentially marine animal.     

The breeding biology of two sympatric species of tropical intertidal hermit crabs,Clibanarius chapini and C. senegalensis

A one-year study of breeding in the two intertidal hermit crabs Clibanarius chapini Schmitt and C. senegalensis Chevreux and Bouvier showed that both species maintain a high reproductive activity throughout the year. Brief low reproductive activities, found in both species, occurred in different months: C. chapini in November, C. senegalensis in May. While these drops cannot be attributed to any recognisable environmental factor, it is suggested that such pattern may result from competition between the two species. Sex-ratio studies indicated slightly more females than males in both species. The maximal size attained by males of both species is considerably greater than that of the females; in C. senegalensis this is very marked. It is suggested that it may be selectively advantageous for a female to attain a smaller maximal size since her brood must also be accomodated within the shell. As expected for continuously breeding species, recruitment of young into the population is also continuous.     

Consistent crustaceans: the identification of stable behavioural syndromes in hermit crabs

Consistent individual variation in behaviour has been termed ‘animal personality’ and has been identified across a range of behavioural contexts including aggression, boldness in response to a threatening stimulus and exploration. When behaviours are correlated across multiple functional behavioural categories or ‘contexts’, ‘behavioural syndromes’ are said to be present. It is possible, however, that behavioural syndromes may also show consistencies. Here we investigated the presence of behavioural syndromes linking startle responses, exploration and aggression in hermit crabs and assessed their stability across two situations (low versus high predation risk). Correlation analyses detected behavioural syndromes between startle responses, a measure of ‘boldness’, and the latency to investigate a novel object, as well as the latency to attack an opponent in an aggressive context. The startle response–investigation and startle response–aggression syndromes were stable between situations, whilst there was a lack of relationship between investigation and aggression in each situation. Here we propose that these consistent individual differences in the expression of behavioural syndromes reveal the presence of animal personality, manifesting in not just one, but a suite of interacting traits.     

Mating success on white-bearded manakin (Manacus manacus) leks: male characteristics and relatedness

Morphological, territorial, and behavioural characteristics were measured on white-bearded manakin (Manacus manacus) males from two leks in two consecutive years. These data were combined with data on marker-inferred relatedness to study possible co-variation with mating success. In one year, male size and male condition were correlated with mating success. In both years, males holding courts nearer the lek centre gained more matings. No observed male display behaviour appeared to be an independently important factor in explaining variance in male mating success. Successful males made more aggressive displays than non-successful males and more displays were between close relatives. Number of aggressive displays increased as the distance between male courts decreased. Mating success in the white-bearded manakin is most likely mediated by a combination of morphological and behavioural characteristics, influencing both male-male competition and female choice. Females could potentially use centrality on the lek as an indicator of male characteristics. However, levels of relatedness may influence spatial arrangement of males on a lek thereby affecting male-male interactions and ultimately influencing patterns of mating success.     

The past ownership of a resource affects the agonistic behavior of hermit crabs

Resource value is often considered the most important nonstrategic variable in the fighting behavior of invertebrates. In our study, we tested whether the experience of shells of a given quality, occupied in the recent past, might affect the agonistic behavior of the hermit crab Pagurus longicarpus. We analyzed the fights battled by 84 test crabs against size-matched unknown rivals before (premanipulation phase) and after (postmanipulation phase) having modified the quality of the domicile shell of the contestants. Specifically, we compared the behavior of crabs that had been subject to either a worsening or an improvement in the quality of their shell with crabs that, although being similarly subject to a shell manipulation, occupied a shell of the same quality as in the premanipulation phase. We found that the crabs subject to a worsening in the quality of their shell were more aggressive than those subject to its improvement and that the former were even more aggressive than those that occupied a bad quality shell also in the premanipulation phase. Crabs seemed not to gather information about the opponent’s shell during fights or not to use this information, most often behaving in accordance with the quality of the domicile shell. These results are clear in showing the role played by the experience of a previously occupied shell, also confirming that the agonistic behavior of P. longicarpus is mainly based on decision rules of the type “own resource value dependency.”     

Variable transfer of detoxified metals from snails to hermit crabs in marine food chains

In any polluted marine environment, different invertebrate species contain markedly different concentrations of heavy metals. Primary producers take metals from seawater, but animals take additional metals from diets of animals, plants and detritus. Metals in a dietary organism of a food chain have varying reactivities and they follow different biochemical pathways. Excess metals are bound by ligands to form insoluble compounds within cytological compartments. These metabolic systems prevent the disruption of normal biochemical reactions by metals. The present work on Mediterranean invertebrates, initiated in Greece in 1993, used digestive glands from three species of marine snail,Monodonta mutabilis (Philippi),Cerithium vulgatum (Bruguière), andMurex trunculus (Linnaeus) as prey tissue, and hermit crabsClibanarius erythropus (Latreille) as predators; the digestive glands and faecal pellets from all animals were analysed by atomic absorption spectroscopy and x-ray microanalysis. Most metals detoxified by the snails are unavailable to the crabs and they pass straight through the gut and appear in the faecal pellets. This applies to significant proportions of the manganese, nickel, copper, zinc and silver which are bound electrostatically to phosphate or covalently to sulphur within membrane-bound intracellular compartments. Cadmium and chromium are transferred to the crabs. In digestive glands of snails, cadmium is bound to soluble highsulphur protein in the cytosol; the cytology of chromium in these animals is not known.     

Ecology of subtropical hermit crabs in S.W. Madagascar: cluster structure and function

The Madagascar coast (both) has a higher density and diversity of hermit crabs than is known from any other locality in the western Indian Ocean. Of the 20 species occurring at Anakao (S.W. Madagascar), 11 aggregated into clusters, including all but one of the species above the subtidal zone. The mean number of hermit crabs and species in clusters varied with several spatial parameters and time. Over 80% of the community clustered in certain habitats in particular tidal zones, whilst as low as 3% clustered in others. The highest intensity of clustering with shore zone was coincident with peak numbers of hermit crabs. The initiation and duration of clusters of hermit crabs above the eulittoral was driven by circadian rhythms, whilst those in the eulittoral were governed by tidal state. Clusters above and below the eulittoral were longer in duration, and those in the subtidal were more temporally variable than those above it. Certain pairs of species showed positive correlations of occurrence and (more rarely) of abundance, and all the correlations (of occurrence) of one, Clibanarius eurysternus, were negative. Positive correlations of occurrence were related to the degree of shell-use commonality between species pairs. Eulittoral species clustered with other individuals of approximately similar size and exchanged shells upon cluster disintegration. There was evidence of a dehydration-reduction function to shell clustering in addition to shell-exchange facilitation. The highly variable species-specific strategies of clustering may be important in alleviating both intra- and interspecific competition in assemblages of similar and highly abundant species.     

Incidence,reproduction and feeding of Stylochus zebra,a polyclad turbellarian symbiont of hermit crabs

The hermit crab Pagurus pollicaris is the common host for the polyclad turbellarian Stylochus zebra in the Atlantic coastal waters from Massachusetts to North Carolina, USA. S. zebra is reported for the first time from two other hermit crabs, Pagurus impressus and Petrochirus diogenes. It was not found with Clibanarius vittatus or Pagurus longicarpus, although the latter serves as a host along the Gulf coast of Florida. The incidence of the polyclad with P. pollicaris in Massachusetts is more than twice that in populations to the south. Multiple infestations (up to 7 worms/crab) occur in over 50% of the infested crabs from Massachusetts, but they are rare elsewhere. Worms living in clear plastic shells with crabs orient in the body whorl dorsal to the host. Egg masses of worms are cemented in the same position within gastropod shells harboring the crabs. In the laboratory, the worm feeds on the gastropod Crepidula plana, a common inhabitant of shells occupied by P. pollicaris. Its feeding behavior is described. The relationship between S. zebra and P. pollicaris appears to be generally commensalistic, but it could be more complicated if the predation of crab embryos observed in the laboratory is confirmed under natural conditions.Contribution No. 755 from the Virginia Institute of Marine Science, Gloucester Point, Virginia, USA.     

Fighting behavior in hermit crabs: the combined effect of resource-holding potential and resource value in Pagurus longicarpus

A study was conducted to determine whether asymmetries in both resource-holding potential (RHP) and resource value (RV) influence dominance and fighting behavior in the hermit crab Pagurus longicarpus. A total of 120 groups of three crabs were observed for 10 min in four experiments that tested all diverse combinations of equal/different RHP (i.e. ‘body size’) and equal/different RV (i.e. ‘shell size’ and ‘shell quality’). In a fifth experiment, dominant and subordinate individuals of the same size category (26 groups) were forced to enter shells of opposite quality than those previously occupied, and then the behavior of the reconstituted original groups was observed for additional 10 min. As expected, crabs in lower quality shells were more willing to initiate and to escalate fights. However, their attacks were directed to any crab of the group, independently of the defender's shell quality, and the fight duration did not vary with the different value of the resources at stake. This may indicate that P. longicarpus is unable to assess the quality of the shells available in its social environment but bases its tactical decisions during fights solely on its own resource. This suggestion was confirmed by the change in the fighting behavior of crabs whose shell quality was experimentally altered. This manipulation induced an overall increase in the intensity of aggression, drastic modification of crab behavior, and inversion of the hierarchy even though these crabs have had previous experiences of wins/losses and were familiar to the other members of the group. In this species, large crab size and/or the occupancy of adequate (and oversized) shells appeared to be the most likely determinant of contest resolution. Individuals seemed to retain a memory of the previously held resource and behaved accordingly.     

GC-EAG-analysis of volatiles from Brussels sprouts plants damaged by two species of Pieris caterpillars: olfactory receptive range of a specialist and a generalist parasitoid wasp species

Summary. Feeding by Pieris brassicae or P. rapae caterpillars on Brussels sprouts plants induces the emission of synomones that attract natural enemies of the caterpillars, Cotesia glomerata, a generalist parasitoid, and C. rubecula, a specialist on P. rapae. Previous research on this tritrophic system has identified a large number of volatiles in the headspace of herbivore-damaged Brussels sprouts plants, and this paper addresses the question which of these volatiles are perceived by the two parasitoid species. Headspace odors from both P. brassicae- and P. rapae-damaged Brussels sprouts plants were analyzed by coupled gas chromatography electro- antennogram (GC-EAG) detection. Twenty volatiles evoked consistent EAG reactions in the antennae of both species and nineteen of these volatiles could be identified with GC-MS. One component that could not be identified due to its low concentration, evoked EAG responses in antennae of C. rubecula only. Possible consequences for searching behavior of the two parasitoid species are discussed.     

Consequences of shell-species preferences for female reproductive success in the hermit crab Pagurus bernhardus

Littoral hermit crabs, Pagurus bernhardus, show a strong preference for Littorina obtusata shells rather than those of Gibbula species. The fitness consequences, in terms of fecundity, for this shell preference is examined for female crabs. Females in the preferred species produced eggs earlier in the season, produced more eggs in the first brood, and produced a second brood more often than did females in the less preferred species. The smaller brood for Gibbula spp. was not a consequence of egg loss from the pleopods due to an unfavourable shape of shell, but rather reflected lower egg production. It is not clear, however, if this differential reproduction is due to direct costs of carrying an unfavourable shell, i.e. the shell impedes reproduction, or whether crabs compete aggressively for favoured shells so that only crabs of low quality inhabit lowquality shells.