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Estrutura populacional e utilização de conchas pelo caranguejo Ermitão Calcinus tibicen (Herbst, 1791) (Crustacea, Decapoda, Diogenidae)

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RESUMO O objetivo deste estudo foi investigar a estrutura populacional e a utilização de conchas pelo caranguejo ermitão Calcinus tibicen (Herbst, 1791) (Crustacea, Decapoda, Diogenidae) do Parque Municipal Marinho de Paripueira, localizado na costa norte do estado de Alagoas entre as coordenadas 09º22'50''-09º30'00'' S e 35º36'14''-35º30'00'' W. A amostragem foi aleatória, realizada mensalmente, durante a baixamar, no período de junho/1998 a maio/1999. No laboratório, as conchas foram identificadas e os caranguejos foram retirados, identificados, avaliados quanto ao sexo e mensurados o comprimento dos escudos cefalotorácicos (CEC). Do total de 1.042 conchas de Gastropoda que foram coletadas, constatou-se que 67 estavam vazias, 9 com Mollusca e 966 habitadas por caranguejos ermitões. Dentre as oito espécies de caranguejos ermitãos registradas para o Parque, foram amostrados 359 indivíduos de C. tibicen (287 machos, 59 fêmeas não ovígeras e 13 fêmeas ovígeras). Os machos apresentaram o comprimento médio do escudo cefalotorácico de 5,90±1,30 mm (CEC mín .: 2,30 mm; CEC máx. : 8,80 mm), enquanto o das fêmeas foi, em média, de 5,09±1,08 mm (CEC mín .: 3,00 mm; CEC máx. : 8,10 mm). Assim pôde-se inferir que os machos são em média maiores 0,81 mm que as fêmeas [t= 4,86; g.l.= 358; p<0,01]; a disparidade na proporção total de macho:fêmea (4,0:1), diferiu significantemente da taxa esperada de 1:1 [χ 2 = 67,28; g.l.= 11; p<0,01]. Calcinus tibicen utiliza 12 espécies de conchas de Gastropoda, todavia 63,33% dos caranguejos ocupam, preferencialmente, as conchas de Astraea tecta olfersii (Phillipi, 1846). A porcentagem de machos, fêmeas não ovígeras e fêmeas ovígeras que utilizam conchas de A. tecta olfersii é de 76,35%, 70,59% e 81,82%, respectivamente. Palavras-Chave: Calcinus tibicen, estrutura populacional, utilização de conchas, Alagoas, Brasil.

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Field studies have suggested that the intertidal hermit crabs of the San Juan Islands of Washington normally occupy snail shells smaller than preferred. In this study the effects of shell size on protection from predation and on hermit crab shell fighting were studied in the laboratory. A predator (Cancer) presented with two hermit crabs (Pagurus granosimanus), identical except in size of occupied shell, preyed upon the hermit in the smaller shell first in 15 out of 16 trials. This results suggests that large shell size confers a selective advantage on the occupying crab. Shell fights involving two hermit crabs (P. hirsutiusculus) of unequal size were observed in which replicates differed only in the shell size of the larger crab. The probability of the larger crab effecting a shell exchange through fighting was shown to increase as the size of its shell decreased. However, shell size was shown to have no effect on the level of aggressiveness as measured by four criteria. The mechanism underlying the former result thus appears to involve a continual high level of general aggressiveness together with an increased tendency associated with occupancy of an inadequate shell by the dominant crab for that crab to evoke a shell exchange during an aggressive interaction.
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We predicted that measurable numbers of new snail shells are transferred daily to hermit crabs in habitats where gastropods frequently prey upon other gastropods. The rate of new shell acquisition by hermit crabs, Pagurus longicarpus, was monitored daily in northeastern Gulf of Mexico salt marshes where crown conchs, Melongena corona, prey heavily upon marsh periwinkles, Littorina irrorata. Periwinkle shells, marked while housing live snails, appeared on P. longicarpus at daily rates ranging from 1 to >20 for selected areas of approximately 60 m2 in three marshes. The maximum number (22.8) of new periwinkle shells appearing among P. longicarpus in the immediate are (300 m2) represented 16.5% of crabs present there each day.
Article
During monthly intervals over a 1-year period, 12,000 empty snail shells were added to a small, isolated, rocky intertidal reef in the San Juan Islands of Washington. The shells added were species normally used by the high intertidal hermit crab, Pagurus hirsutiusculus, and were placed in locations accessible to that species. The shell additions resulted in an increase in density of P. hirsutiusculus at the experimental reef, whereas no density change occurred at a nearby control reef, indicating the importance of shells as a limiting resource. To establish the generality of shell limitation, the hermit crab populations of four unmolested rocky intertidal sites (three of which are typical hermit crab habitats) were quantitatively samples to obtain species compositions and size distributions of hermit crabs, their shells, and unoccupied shells. Shell preference experiments determined the preferred shell sizes and species for each hermit crab species. Except for small size classes, empty shells were rate at the three typical areas. In addition, hermit crab size distributions followed shell size distributions, and all but small hermit crabs of three species occupied shells smaller than the preferred size. These results support the conclusion that empty shells are a limiting resource for these hermit crabs. Since shells constitute a common, necessary resource in short supply, these hermit crabs are in competition for available shells. The fourth area, chosen for its unusual shell-availability characteristics, exhibited a different pattern of shell utilization not suggesting shell limitation. Shell occupancy at the three representative intertidal sites was examined to determine the strength of the relationship between hermit crab species composition and resource availability. Though resource partitioning was demonstrated, the presence and numbers of each hermit crab species and its preferred shell types were poorly correlated. Differences in hermit crab species composition are explained by differences in the physical habitat, and collections from other areas show that the same shell species can support different hermit crab species in different but adjacent habitat types. Thus, the mechanism allowing coexistence apparently involves both resource and habitat partitioning.
Article
A typical hermit crab protects its soft parts by enclosing them in a gastropod shell. Empty shells are often durable enough that one could provide protection for a crab's entire lifetime. However, crabs choose shells that fit their bodies closely, and crabs cannot continue to grow unless they have a continuous supply of shells [except Pagurus prideauxi (Pike and Williamson, 1959) P. bernhardus (Jensen, 1975), and numerous other species (Nyblade, 1974) whose shells support colonial organisms that grow continuously forward from the lip of the shell]. If hermit crabs require a continuous supply of shells, then the shell supply rate may influence crab numbers. An opportunity to test this hypothesis arose during long-term studies of snail populations on a rocky shore area, Shady Cove, 0.5 mile north of Friday Harbor Laboratories, San Juan Island, Washington. Between August 1967 and August 1970, 4272 specimens of Thais lainellosa and 582 of T. eniarginata from the 200 m2 study area were given individually num bered tags (Spight 1974) . About 40% of the snails died each year, and as snails died, their tagged shells were acquired by the hermit crabs of the vicinity. The first crab with a tagged shell was found during May, 1968, and progressively more were found in succeeding months. Since the crabs used many of the tagged shells, the crabs provided a valuable means to verify snail deaths, and deliberate censuses of tagged crabs were undertaken. These census data will be examined here for correlations between changes in the rate of shell supply and changes in the portion of the crab population using shells of Thais.
Article
Hermit crabs are obligate users of gastropod shells. Shell availability is often the limiting factor for crab population size. Crabs have an extensive behavioral repertoire for obtaining shells. Here we extend our studies of the chemical ability of crabs to locate the shells of dead and dying gastropods from a distance. We show that peptide cues generated by the action of specific proteases on specific substrates attract crabs. The specificity of the crab response is dependent upon the type of substrate as well as the suit of enzymes attacking the substrate. Single specific enzymes are not as effective as mixtures of enzymes in generating cues from pure (and totally foreign) substrates such as ovalbumin. However, the activation of trypsinogen by enterokinase yields only a single hexapeptide and results in potent crab attraction. We conclude that the specific sequence of the peptide determines attraction. Thus, the key to crab attraction is the presence of a particular sequence in a substrate and the ability of enzymes or mixtures of enzymes to release that sequence.
Article
Field studies with three common local species of hermit crabs,Clibanarius vittatus, Pagurus longicarpus, andPagurus pollicaris, showed that these crabs responded behaviorally to chemicals originating from crushed conspecifics. Hermit crabs are attracted specifically and in a manner similar to previously reported crab responses to odors from dead gastropods. Responses byC. vittatus to both kinds of odor are of three types: (1) aggregation/shell investigation responses (previously reported for odors from dead gastropods), characterized by increased locomotor activity, investigation of shells in the vicinity, and switching into empty shells; (2) alarm responses, in which crabs flee the area; and (3) withdrawal responses, in which crabs pull into their shells and do not come out. Studies withC. vittatus showed that the stimulatory chemicals originate from hemolymph, are less than 500 D, adsorb to octadecyl silica, and are recovered by elution with 20% methanol. Responses ofC. vittatus are dependent upon crab size, type of shell occupied, and shell fit. Chemicals originating from dead conspecifics provide a forum for shell acquisition by crabs in relatively small shells and alarm by crabs in relatively large shells.
Article
The availability of gastropod shells to hermit crabs in the Newport River Estuary, Beaufort, N.C. has been assessed by determining the numbers of usuable shells occurring in characteristic subtidal habitats and by measuring shell size adequacy. The proportion of useable shells occupied by hermit crabs ranged from 58–99 % and many of the shells not used by hermit crabs were judged unavailable because they were occupied by sipunculids or only uncovered by the dredge. The shell adequacy index (shell size occupied/shell size preferred) was significantly below 1.0 for the largest species (Pagurus pollicaris Say) in the one location where sufficient numbers were collected and for the next largest species (P. longicarpus Say) in three of the four locations where it was collected. The shell size adequacy index for the smallest species (P. annulipes Stimpson) did not differ significantly from 1.0 in either of the two locations in which it was found. These observations suggest that the availability of gastropod shells plays a significant rôle in limiting the abundance of at least the larger hermit crabs.
Article
Pagurus longicarpus from two geographiclocations were raised in the same en vironment in three species of gastropod shell. These shell species differed in shape and maximum size. Crabs in small, high-spired shells attained smaller sizes than those in large, low-spired shells. Further, the relative growth rates of male crabs showed differences related to shell differences. Males in small, high-spired shells pro duced relatively longer claws and greater right/left claw asymmetry than males in large, low-spired shells. These results show the close interaction between hermit crabs and utilized shells and may explain the geographic variation ofP. longicarpus. Along the Atlantic coast, southern crabs are smaller and have relatively longer claws and greater right/left claw asymmetry than northern crabs. Southern crabs utilize small, high-spired shells almost entirely, whereas northern crabs utilize a high proportion oflarge, low-spired shells. Size and shape differences between geographic populations of P. longicarpus thus may be due to differences in inhabited shells.
Article
Discorsopagurus schmitti is a hermit crab that inhabits empty polychaete tubes in the North Pacific. Here we describe some aspects of its life history (relative growth, population structure, reproductive biology, and incidence of parasitism) and discuss the relationships among them. Unlike most hermits, the two sexes of this species have similar size distributions. In both sexes, larger body size is accompanied by a higher reproductive output (larger clutch size in females and more intrasex competitive po- tential in males). The energy the females expend in egg production might be equaled in this species by the energy the males expend in supporting parasites. In fact, the ex- tent of infestation by two rhizocephalans (Peltogaster boschmae and Thilacoplethus (= Thompsonia) reinhardi) is more pronounced in males, especially those in the larger size classes. However, rhizocephalans have little effect on their hosts; growth and secondary sexual characters are not influenced. The only morphological modification is the more frequent loss of the second pleopod. Infected hermits also showed a mock parental behavior, fanning the externae with the pleopods as ovigerous females fan their eggs. Larvae are released in sequential bursts, and hatching occurs exclusively at night, possibly to minimize predation by diurnal fishes. Hatching is also synchronized with neap tides, which might keep the larvae from being flushed out into open waters. In a species whose habitat (sabellarian bioherms) is rare and quite unpredictable, it is beneficial to retain larvae near the parental population.
Article
The supply and quality of empty gastropod shells may play important roles in the ecology and evo- lution of hermit crabs. We compare the life histories of three subtidal hermit crabs in Nantucket Harbor, Mas- sachusetts: Pagurus annulipes, P. longicarpus, and P. pol- licaris. Specifically, we examine seasonal patterns of re- production in females, male and female size structure, reproductive effort, and temporal patterns of larval abun- dance. We also compare shell size among the three species. Life-history features vary with size among the three spe- cies. The smallest species (P. annulipes) reproduce soon after metamorphosis and have a high reproductive effort. The two larger species (P. longicarpus and P. pollicaris) delayed reproduction to an intermediate size, and have lower reproductive efforts than P. annulipes. There is no effect of body size on reproduction in P. annulipes, but there is a strong positive effect in P. longicarpus and P. pollicaris. Seasonal patterns of early stage larvae correlated with seasonal patterns of ovigery in all three species, with highest larval densities sampled in P. annulipes and P. longicarpus. Size differences among species were related to patterns of shell usage. Male and female P. annulipes were always found in large shells relative to body size. In comparison, male and female P. longicarpus and P. pol- licaris were found in small shells compared to body size. We suggest that early maturity and high reproductive ef- fort have evolved in response to a high risk of mortality associated with small shells. Delayed maturity and low reproductive effort are favored in species that reach a size refuge from shell-crushing predators. Effects of shell lim-
Article
Das Verhältnis der Geschlechter verändert sich bei Copepoda mit zunehmender Wassertiefe zu Gunsten des weiblichen Geschlechtes. Bei knappen Futterverhältnissen erhöht diese Erscheinung die Fruchtbarkeit der Art.
Article
SYNOPSIS. AS an ecotone, the littoral environment is often complex and is generally rich in numbers and species of organisms. The disadvantages of the biotope in terms of exposure to physical factors of both the marine and terrestrial environments are patent, but the advantages are not so evident. The continual replenishment of food brought from the sea, particularly for detritus-feeding animals such as hermit crabs, coupled with the possibility and ability to establish microhabitatswith microclimatic conditions may constitute the principal advantage. Escape from specialized predators may also be important. Hermit crabs have successfully exploited most intertidal environments. As members of the "benthic detritus-feeding guild" food is abundant, and by utilizing their shells in conjunction with movements within the littoral zone they have met successfully most of the rigors of the environment. The shell also provides some protection from predation, particularly from non-specialized predators.Indeed, the behavioral patterns associated with living in shells which permit the shell to serve as a microhabitat constitute the major adaptation enabling the hermit crabs to exploit the intertidal environment so successfully.
Article
Clibanarius digueti shows strong sexual dimorphism with respect to size, with almost no overlap between adult males and females. Both sexes gain in fitness-related parameters with increasing body size. Courting males average 35% heavier than noncourting males; males in the largest-size classes, which make up <1% of the total male population, accounted for 12% of reproductive activity. Female mating success apparently is no affected by body size, since breeding frequencies did not vary with size. Courting pairs are formed non-assortatively, indicating that males are not choosing females on the basis of size. Females did show an increase in clutch size with body size, but the rate of increase is among the lowest recorded for decapod crustaceans. If female fecundity in C. digueti increased isometrically with body size, as is typical in decapod crustaceans, then female fitness would actually increase more rapidly than male fitness with body size. This modest size-related fecundity gain in females is unexplained (possibly resulting from increased shell limitations on larger crabs), but it leads to the conclusion that selection for large size is stronger in males, a necessary condition for sexual differences in selection to have a role in sexual size dimorphism. -from Author
Article
The importance of differential mortality between sexes of a dioecious population is discussed. From pertinent literature and a simple theoretical treatment I conclude that potential rate of evolution may be greater than existing theory suggests in species in which males suffer higher mortality than females. Species with this type of selection structure should be better able to track short-term changes in their environment genetically, should have greater niche breadths, and would be more efficient colonizers of new environments than are species for which selection intensities are the same in males and females.
Article
Shell preferences, as shown by laboratory choice experiments, are important determinants of shell utilization under natural conditions. Size and shell species preferences of the hermit crab Calcinus tibicen were determined for the three most occupied [Stramonita haemastoma (Linnaeus, 1767), Leucozonia nassa (Gmelin, 1791) and Pisania auritula (Link, 1807)] shell species along the rocky shore of Grande beach, Ubatuba, Brazil, taking into account the sexual condition of the individuals. All experiments were conducted under laboratory conditions using a glass aquarium where the hermit crabs (independent on their sex condition) were placed naked with a large number of shells of appropriate sizes. The chosen shells were determined after 72 h. The preferred shell species and size were determined by regression analysis. C. tibicen showed no significant choice among the three gastropod shell species. Shell size experiments revealed that the preference of hermit crabs was strongly associated with shell weight and internal volume. The shell adequacy index (SAI) decreased with increasing crab size and showed that the population was occupying relatively adequate shells (SAI=0.99±0.19). The present data lead us to conclude that shell selection by hermit crabs involves individual and sexual preferences taking into account the shell features that best provide protection and survival, principally in the rocky intertidal studied area, characterized by intense wave action.
Article
Hermit crabs respond to odors signaling potential shell availability by (1) withdrawing if they are in relatively large shells; (2) fleeing if the shells are ones they would occupy if given choices; (3) investigating if the shells occupied are relatively small. We used these behavioral responses as measures of shell fit to assess shell resources of Clibanarius vittatus (Bosc). From analysis of responses we conclude shell resources are dynamic. Behavioral tests suggest many crabs occupied relatively large shells in the spring and relatively small shells in the fall. Crabs in shells in which they would remain when presented with excess shells never comprised more than 30% of the population at any time of the year. Behavior of subpopulations of crabs from sand/mud and oyster reef habitats and crabs on land or in water at low tide was determined. In the fall, crabs whose behavior indicated they occupied relatively small shells for their size were found mainly in sand/mud habitats and remained in the water at low tide. Crabs whose behavior suggested shells they occupied that fit well were rare. The few that were found were found mainly in sand/mud habitats and were equally distributed on land and water. Crabs behaving as if shells were large for their size were found distributed evenly throughout oyster reef and sand/mud habitats and on both land and in water at low tide. Distributional results could not be explained by reduced mobility. Movement studies showed that even crabs in weighted shells should not be trapped by a receding tide. We postulate crab habitat choice is a behavioral adjustment that compensates for imperfect shell fit.
Article
Two species of Mediterranean hermit crabs, Calcinus ornatus (Roux) and Clibanarius erythropus (Latreille) were studied in the laboratory to examine some aspects of the “coexistence problem” (Hazlett, 1981). Evidence suggests that no competition exists between these sympatric species. First, although they both use the same type and size of shells, the two species occupy shells which differ in detail, Calcinus preferring epibiotic-covered shells. Second, the two species selected different microhabitats and showed different physiological resistance to physical stress: Clibanarius could resist dehydration and extremes of temperature and salinity better than Calcinus. Third, from the behavioural point of view, Clibanarius was more mobile than Calcinus, which resulted in faster exploitation of empty shells, and exhibited a greater tendency to aggregate. In turn, clustering may enhance the possibility of beneficial intraspecific shell exchange by triggering off a chain reaction; such an event, however, is rare. Conversely, neither interspecific shell switching nor dominance-subordinance relationships existed, although the two species seem to speak the same “language”.
Article
It has been proposed in the literature that intraspecific competition in hermit crabs, mediated by a succession of shell exchanges, would lead to members of a given size class experiencing approximately the same level of shell adequacy. This hypothesis was modified and extended to predict that intraspecific competition should result in the maximization of the correlation between hermit crab size and shell size, regardless of the level of shell adequacy.The prediction has been tested by establishing laboratory populations of the hermit crab Paguruslongicarpus Say, and simulating these populations using a computer program which assumed constant motivational states and dominance relationships. The populations at the beginning of the experiment consisted of 19–21 individuals inhabiting shells as a result of a process that did not allow actual shell selection. The populations were divided among three treatments based on the availability of 0, 10, or 20 shells in addition to those inhabited initially.At the end of the first week, all populations displayed an increased correlation between hermit crab weight and shell weight, and these values were similar to those generated by the computer simulation. The values at the end of the second week, however, showed a noticeable decline in the populations with no empty shells available. In addition, these populations had the largest number of injuries, which could only be the result of aggressive encounters between hermit crabs.The results of these experiments are used to formulate a general model of hermit crab behavior under different levels of shell availability and shell adequacy.