Cardisoma Hirtipes Research Articles

Erratum to: Characterization of microsatellite markers from the commodity species Cardisoma guanhumi Latreille and the Christmas Island blue crab (Discoplax celeste)

Erratum to: Characterization of microsatellite markers from the commodity species Cardisoma guanhumi Latreille and the Christmas Island blue crab (Discoplax celeste)

Characterization of microsatellite markers from the commodity species Cardisoma guanhumi Latreille and the Christmas Island blue crab (Discoplax celeste)

Cardisoma guanhumi Latreille, the blue land crab, is overharvested throughout its range, resulting in harvesting regulations in multiple countries/protectorates. A lack of polymorphic markers hampers genetic-based conservation for the species. Here, we present 13 loci, eight of which are polymorphic in the heavily collected popu- lations of C. guanhumi on Andros Island, The Bahamas. Overharvesting of Androsian crabs may have reduced diversity, so both monomorphic and polymorphic loci are presented. Five of the loci were found to be polymorphic in Discoplax celeste, the Christmas Island blue crab.

Roles of crustacean hyperglycaemic hormone in ionic and metabolic homeostasis in the Christmas Island Blue crabDiscoplax celeste

There is a growing body of evidence implicating the involvement of crustacean hyperglycaemic hormone (CHH) in ionic homeostasis in decapod crustaceans. However, little is known regarding hormonally influenced osmoregulatory processes in terrestrial decapods. As many terrestrial decapods experience opposing seasonal demands upon ionoregulatory physiologies, we reasoned that these would make interesting models in which to study the effect of CHH upon these phenomena. In particular, those (tropical) species that also undergo seasonal migrations might be especially informative, as we know relatively little regarding the nature of CHHs in terrestrial decapods, and hormonally mediated responses to seasonal changes in metabolic demands might also be superimposed or otherwise integrated with those associated with ionic homeostasis. Using Discoplax celeste as a model crab that experiences seasonal extremes in water availability, and exhibits diurnal and migratory activity patterns, we identified two CHHs in the sinus gland. We biochemically characterised (cDNA cloning) one CHH and functionally characterised (in terms of dose-dependent hyperglycaemic responses and glucose-dependent negative feedback loops) both CHHs. Whole-animal in situ branchial chamber (22)NaCl perfusion experiments showed that injection of both CHHs increased gill Na(+) uptake in a seasonally dependent manner, and (51)Cr-EDTA clearance experiments demonstrated that CHH increased urine production by the antennal gland. Seasonal and salinity-dependent differences in haemolymph CHH titre further implicated CHH in osmoregulatory processes. Intriguingly, CHH appeared to have no effect on gill Na(+)/K(+)-ATPase or V-ATPase activity, suggesting unknown mechanisms of this hormone's action on Na(+) transport across gill epithelia.

Population Structure of the Christmas Island Blue Crab, Discoplax hirtipes (Decapoda: Brachyura: Gecarcinidae) on Christmas Island, Indian Ocean

The population structure of the freshwater land crab Discoplax hirtipes (Gecarcinidae) was studied on Christmas Island, Indian Ocean, to which this species is endemic in its blue colour form. Despite previous overexploitation of this crab, this is the first such study to take place for this species on Christmas Island. Surveys were conducted in the dry (non-migration) season, at Ross Hill Gardens, which is one of several permanent ‘residential areas’ inhabited by D. hirtipes. The sex ratio was found to be skewed in favour of males 2:1. Similarly to other gecarcinid species, male crabs were found to grow larger than females in terms of body weight, carapace width and chelae size (length and width). During the survey, few juveniles were found, which could suggest an ageing population. Despite being protected by law on Christmas Island, this is potentially worrying for a species that due to its restricted distribution continues to be especially vulnerable to outside threats, including that of aggressive invasive species and long term habitat destruction.

Functional morphology of the gastric mills of carnivorous, omnivorous, and herbivorous land crabs

Terrestrial decapods consume a wide variety of plant and animal material. The potential adaptations of carnivorous, omnivorous, and herbivorous terrestrial crustaceans were studied by examining the functional morphology of the gastric mill. Two closely related species from each feeding preference group were examined to identify which features of the mill were due to phylogeny and which were due to adaptation. The morphology of the gastric mill matched the diet well; the gastric mills of the carnivorous species (Geograpsus grayi and Geograpsus crinipes) possessed a blunt, rounded medial tooth and flattened lateral teeth with a longitudinal grinding groove. These features make them well suited to a carnivorous diet of soft animal tissue as well as hard material, such as arthropod exoskeleton. In contrast, the mill of the herbivorous gecarcinids (Gecarcoidea natalis and Discoplax hirtipes) consisted of a medial tooth with sharp transverse ridges and lateral teeth with sharp interlocking cusps and ridges and no grinding surface. These features would efficiently shred fibrous plant material. The morphology of the mill of the omnivorous coenobitids (Coenobita perlatus and Birgus latro) was more generalized toward a mixed diet. However, the mill of B. latro was more adapted to deal with highly nutritious food items, such as nuts and heavily calcified decapods. Its mill possessed lateral teeth with extended ridges, which sat close to the calcified cardiopyloric valve to form a flattened floor. Hard items trapped in the mill would be crushed against this surface by the medial tooth.

A role for CHH in the regulation of kidney-like function in freshwater land-crabs: A study of the Christmas Island blue crab, Discoplax hirtipes

A role for CHH in the regulation of kidney-like function in freshwater land-crabs: A study of the Christmas Island blue crab, Discoplax hirtipes

Endogenous production of endo-β-1,4-glucanase by decapod crustaceans

The potential ability to produce cellulase enzymes endogenously was examined in decapods crustaceans including the herbivorous gecarcinid land crabs Gecarcoidea natalis and Discoplax hirtipes, the amphibious freshwater crab Austrothelphusa transversa, the terrestrial hermit crab, Coenobita variabilis the parastacid crayfish Euastacus, and the crayfish Cherax destructor. The midgut gland of both G. natalis and D. hirtipes contained substantial total cellulase activities and activities of the cellulase enzymes endo-beta-1,4-glucanase and beta-glucosidase. With the exception of total cellulase and beta-glucosidase from D. hirtipes, the enzyme activities within the midgut gland were higher than those within the digestive juice. Hence, the enzyme activities appear to reside predominantly within midgut gland, providing indirect evidence for endogenous synthesis of cellulase enzymes by this tissue. A 900 bp cDNA fragment encoding a portion of the endo-beta-1,4-glucanase amino acid sequence was amplified by RT-PCR using RNA isolated from the midgut gland of C. destructor, Euastacus, A. transversa and C. variabilis. This provided direct evidence for the endogenous production of endo-beta-1,4-glucanase. The 900 bp fragment was also amplified from genomic DNA isolated from the skeletal muscle of G. natalis and D. hirtipes, clearly indicating that the gene encoding endo-beta-1,4-glucanase is also present in these two species. As this group of evolutionary diverse crustacean species possesses and expresses the endo-beta-1,4-glucanase gene it is likely that decapod crustaceans generally produce cellulases endogenously and are able to digest cellulose.

Respiratory and acid–base responses during migration and to exercise by the terrestrial crabDiscoplax (Cardisoma) hirtipes, with regard to season, humidity and behaviour

The terrestrial crab Discoplax hirtipes (formerly Cardisoma hirtipes) exhibits a seasonally dichotomous activity pattern governed by the seasonal rainfall on Christmas Island, with a breeding migration in the wet season. Greater activity in the wet season reflects a release of constraints on ion and water balance independent of changes in exercise physiology. The respiratory responses to walking exercise by D. hirtipes were assessed with regard to humidity and season. In the laboratory, crabs walked 38% faster when humidity was high, while the O(2) uptake across the lung became diffusion limited despite a Ca(2+)-induced increase in O(2) affinity of the haemocyanin. Crabs walking in 90% relative humidity exhibited a larger metabolic acidosis while re-oxidation of l-lactate was only 0.49 mmol l(-1) h(-1). The wet-season crabs were more active and exhibited a respiratory acidosis compared with the quiescent dry-season crabs. The migration was close to the limit of the aerobic scope of the crabs, and the pulmonary oxygen partial pressure (P(O(2))) was depressed, the O(2) uptake diffusion limited and the arterial-venous P(O(2)) difference diminished. Additional, enforced exercise induced a metabolic acidosis. The optimum strategy for migration would be walking continuously but at a speed within the aerobic scope. D. hirtipes is influenced by seasonal rain and responds to lower ambient humidity by limiting exercise. The behavioural response is paramount since the changes in respiratory status were determined primarily by the differences in commitment to, and investment in, walking and not by direct effects of humidity on respiratory physiology.

Larval Morphology and Salinity Tolerance of a Land Crab from West Africa, Cardisoma Armatum (Brachyura: Grapsoidea: Gecarcinidae)

The complete larval development of a terrestrial crab from West Africa, Cardisoma armatum Herklots, 1851, was studied in laboratory rearing experiments carried out at various salinities ranging from 0.2& to 45&. Six zoeal stages and one megalopa are described and illustrated. Our experimental results showed that zoeal stages of C. armatum are fairly euryhaline, zoea I to IV tolerating a salinity range of 15–45&, and 15–35& during later development. However, salinity 15& tended to cause higher mortality and a significantly delayed development in most stages, while 25& allowed for maximum survival through metamorphosis. These observations suggest that C. armatum follows a limited export strategy, where the adults may live in brackish or even freshwater habitats, while a successful larval development is possible only in estuarine or coastal waters with higher salinities, presumbly with an optimum in the lower parts of estuaries with 25&. Before this study, only an incomplete description of the first zoeal stage of C. armatum was available, and complete larval development had been known only for C. carnifex and C. guanhumi. In the present paper, the larval morphologies of these three congeneric species are compared. Within the Gecarcinidae, the complete larval development has been described also for Discoplax hirtipes and Gecarcinus lateralis, while only data for the morphology of the first zoeal stage are available for the other two genera of this family, Epigrapsus and Gecarcoidea. Hence, there are at present no sufficient data, in particular on megalopal morphology, to allow for conclusive intergeneric comparison and identification of familial characters. Gecarcinid zoeal morphology, as far as this is known, is briefly discussed in relation to that in other grapsoid families.

Presence and properties of cellulase and hemicellulase enzymes of the gecarcinid land crabs Gecarcoidea natalis and Discoplax hirtipes

Digestive juice from the herbivorous gecarcinid land crabs Gecarcoidea natalis and Discoplax hirtipes exhibited total cellulase activity and activities of two cellulase enzymes; endo-beta-1,4-glucanase and beta-1,4-glucosidase. These enzymes hydrolysed native cellulose to glucose. The digestive juice of both species also contained laminarinase, licheninase and xylanase, which hydrolysed laminarin, lichenin and xylan, respectively, to component sugars. The pH optima of beta-1,4-glucosidase, endo-beta-1,4-glucanase and total cellulase from G. natalis were 4-5.5, 5.5 and 5.5-7, respectively. In the digestive juice from D. hirtipes, the corresponding values were 4-7, 5.5-7 and 4-9, respectively. The pH of the digestive juice was 6.69+/-0.03 for G. natalis and 6.03+/-0.04 for D. hirtipes and it is likely that the cellulases operate near maximally in vivo. In G. natalis, total cellulase activity and endo-beta-1,4-glucanase activity were higher than in D. hirtipes, and the former species can thus hydrolyse cellulose more rapidly. beta-1,4-glucosidase from G. natalis was inhibited less by glucono-d-lactone (K(i)=11.12 mmol l(-1)) than was the beta-1,4-glucosidase from D. hirtipes (K(i)=4.53 mmol l(-1)). The greater resistance to inhibition by the beta-1,4-glucosidase from G. natalis may contribute to the efficiency of the cellulase system in vivo by counteracting the effects of product inhibition and possibly dietary tannins. The activity of beta-1,4-glucosidase in the digestive juice of D. hirtipes was higher than that of G. natalis.

Locomotion, respiratory physiology, and energetics of amphibious and terrestrial crabs.

The transition from breathing air to breathing water requires physiological and morphological adaptations. The study of crustaceans in transitional habitats provides important information as to the nature of these adaptations. This article addresses the physiology of air breathing in amphibious and terrestrial crabs and their relative locomotor abilities. Potamonautes warreni is an apparently amphibious freshwater crab from southern Africa, Cardisoma hirtipes is an air-breathing gecarcinid crab with some dependency on freshwater, and Gecarcoidea natalis is an obligate air-breathing gecarcinid endemic to Christmas Island in the Indian Ocean. All three species have well-developed lungs but retain gills and show seasonally different activity patterns that, in the gercarcinids, especially G. natalis, include long-distance breeding migrations. The three species were better at breathing air than water, but P. warreni was the best at breathing water. Cardisoma hirtipes is essentially an obligate air breather and appears to experience facultative hypometabolism during immersion. Cardisoma hirtipes has a haemocyanin with a high affinity for O(2) that facilitates loading from air but makes 30% of the Hc bound O(2) inaccessible. The gecarcinids but not P. warreni show increased diffusion limitation for O(2) over the lung during exercise. Gecarcoidea natalis outperforms C. hirtipes by virtue of a unique haemolymph shunt from the lung into the gills. Paradoxically, it is modifications of the gills for aerial O(2) uptake in G. natalis that allow for relatively greater haemolymph oxygenation. Despite showing decreased arterial-venous DeltaPo(2), P. warreni increased the arterial-venous Delta[O(2)] with no recourse to anaerobiosis during 5 min exercise. In the short term, P. warreni is more adept at walking than C. hirtipes. The breeding migrations of C. hirtipes and G. natalis were completely aerobic, but G. natalis walk farther and probably faster. Seasonal changes in underlying metabolism of G. natalis are strongly implied, including variations in hyperglycaemic hormone, variable basal metabolic rates, and a diel alkalosis present only in migrating crabs. The persistent dependence on water for reproduction is a determining factor in the biology of air-breathing crabs. The annual migrations include costs other than locomotion, for example, burrow construction and intermale competition. Estimates of costs that consider walking alone will underestimate the metabolic and stored fuel requirements for successful reproduction.

Digestive strategies in two species of leaf-eating land crabs (Brachyura: Gecarcinidae) in a rain forest.

Two species of herbivorous land crabs from Christmas Island, Cardisoma hirtipes and Gecarcoidea natalis, overlap in both diet and distribution. This study compared the dietary preferences and digestive capabilities of these two species on a diet of leaf litter to establish the digestive strategies each adopts and the likely degree of competition for food. C. hirtipes preferred green to yellow or brown leaves of Ficus macrophylla in short-term food-choice experiments. Brown leaves were least favoured. G. natalis showed no preference for the different leaf types and in the field ate chiefly brown and decomposing leaf litter. When fed green leaves, C. hirtipes had a low food intake (4.5+/-0.36 g kg-1 d-1) and a short retention time for food, and the readily digestible components of the diet constituted greater than 84% of the dry matter assimilated. When fed brown leaves, the intake was increased 3.3 times, but retention time remained short, and assimilation coefficients for all nutrients were low. The readily digestible fraction of the diet made the chief contribution to dry matter assimilation (69%), and hemicellulose (19%) and cellulose (21%) were also significantly used. This pattern of food intake and assimilation contrasts with that for G. natalis, which had a low intake of brown leaves and a longer retention time associated with higher nutrient assimilation, particularly of complex polysaccharides. It is suggested that through their feeding preferences and habits, these two sympatric species use opposite ends of the leaf litter quality spectrum on Christmas Island.

Water and ion balance and nitrogenous excretion as limitations to terrestrial excursion in the Christmas Island blue crab,Cardisoma hirtipes (Dana)

Cardisoma hirtipes appears from the species distribution to be dependent on fresh water. The ability of C. hirtipes to maintain ion and water balance and nitrogenous excretion in the absence of free water (water in which the crab can immerse itself) was assessed in the laboratory and in the field during both the wet and dry seasons. During enforced exposure to air for 9 days (only drinking water provided), the osmotic pressure and composition of both the haemolymph and urine remained constant, although the urine differed in composition to the haemolymph. The antennal gland reabsorbed Ca and Mg from the urine. The final excretory product (P) was dilute, containing only 10% of the concentration of ions measured in the haemolymph. Water loss to air was minimised by reduced P flow, but drinking was insufficient to prevent dehydration. Therefore, C. hirtipes might require periodic immersion to maintain long-term water balance. Nitrogen excretion to air was negligible compared to excretion to water, and after 9 days in air C. hirtipes excreted N at an elevated rate within the first 2 min of submersion. In the field, crabs restricted from access to water had urine and haemolymph osmotic pressure and composition similar to unrestricted, free-ranging crabs. The osmotic pressure was highest in crabs sampled in the wet season, although nitrogenous excretion rates were similar during the wet and dry season for both free-ranging and restricted crabs. The distribution of C. hirtipes is dependent on water availability, but under humid conditions water from drinking and food might balance short-term losses. The extent of terrestrial excursions by C. hirtipes is limited by dependency on water for nitrogen excretion. J. Exp. Zool. 279:537–548, 1997.© 1997 Wiley-Liss, Inc.

Water and ion balance and nitrogenous excretion as limitations to terrestrial excursion in the Christmas Island blue crab, Cardisoma hirtipes (Dana)

Water and ion balance and nitrogenous excretion as limitations to terrestrial excursion in the Christmas Island blue crab, Cardisoma hirtipes (Dana)

Respiratory, Acid-Base, and Metabolic Responses of the Christmas Island Blue Crab, Cardisoma hirtipes (Dana), during Simulated Environmental Conditions

The dependency of the Christmas Island blue crab, Cardisoma hirtipes, on fresh water for respiratory gas exchange and transport was investigated in laboratory simulations. The gas exchange rates of air-breathing C. hirtipes were similar to those of other land crabs but decreased to 20% in submerged crabs. Crabs with access to air maintained arterial and pulmonary O2 content (CO2) and partial pressure (PO2), while in submerged crabs the PO2 and CO2 rapidly decreased (by 50%). There was no anaerobiosis, but haemolymph glucose concentration and cardiac output decreased when crabs were submersed, which suggests a hypometabolic state. Submersion induced a metabolic rather than a respiratory alkalosis, and since respiratory gas exchange was low, CO2 excretion to water was unimportant. Cardisoma hirtipes haemocyanin (Hc) has high O2 affinity but low pH sensitivity, which facilitates O2 uptake from hypoxic environments. The high Hc-O2 affinity supports O2 loading but may prevent access to a venous O2 reserve. Calcium, magnesium, and urate, but not L-lactate, were effectors of Hc-O2 affinity. In submerged crabs increased circulating urate maintained haemolymph O2 content. The CO2 capacitance and nonbicarbonate buffering of the haemolymph were relatively low. A significant Haldane effect seemed important for CO2 excretion but would require CO2 and O2 exchange to occur at the same organ (gills or lungs). Submersion interferes with respiration and is not needed for haemolymph acid-base balance; thus; C. hirtipes is an air-breathing crab.

The Respiratory Gas Transport, Acid-Base State, Ion and Metabolite Status of the Christmas Island Blue Crab,Cardisoma hirtipes(Dana) Assessed in Situ with Respect to Immersion

Christmas Island blue crabs, Cardisoma hirtipes, were sampled in the field during two different seasons (November 1993 and June 1994) to assess the ability of this species to maintain gas exchange in air and water. Hemolymph samples from the pulmonary vessel, pericardial cavity, and infrabranchial sinuses were taken from crabs breathing air and after 30 min of immersion. The pulmonary partial pressure of O₂ (Ppo2) decreased from >90 Torr in air-breathing crabs to <15 Torr after 30 min of immersion but there was no increase in L-lactate in the hemolymph or the muscle tissue. Hemocyanin (Hc) in the pulmonary hemolymph was 100% saturated in air-breathing crabs but O₂ content and saturation were quite variable in the immersed crabs between seasons. The variability of hemolymph O₂ content in immersed animals was partially attributed to changes in He affinity, which in turn were brought about by different conditions of the spring water that the crabs were immersed in during the two sampling seasons. The spring water supplying the habitat was variably CaCO₃-enriched and hypercapnic. Blue crabs immersed in this water exhibited a marked metabolic alkalosis rather than a respiratory alkalosis that might result from hyperventilation in water. It is hypothesized that C. hirtipes trap air in their branchial chambers during natural submergence, which compromises gas exchange, but that net base loading from the water may occur across the gills. In the field, C. hirtipes is clearly not dependent on water for respiratory or acid-base regulation, exhibiting characteristics of an obligate air breather. The hemolymph osmotic pressure of C. hirtipes was low, ∼530 mOsmol · kg⁻¹, thus reducing the gradient for ion loss into the fresh water that these crabs inhabit. The requirement on water for osmotic and ionic regulation as well as nitrogen excretion requires investigation.

CALCIUM AND MAGNESIUM BALANCE DURING MOLTING IN LAND CRABS

ABSTRACT Calcium and magnesium contents were measured in the terrestrial crabs Cardisoma hirtipes, Gecarcoidea natalis, Geograpsus grayi, and Ocypode cordimana in relation to the intermolt cycle. Contents of these elements were of a similar order to those of marine decapod crustaceans with the exception of the Ca:Mg ratio in Geograpsus grayi (13:2) which was higher than in the other species. Regression equations relating Ca and Mg content to body size are supplied for each species. Behavioral adaptations allowed essentially all calcium and magnesium to be retained through the molt. Crabs molted in burrows (gecarcinids and Ocypode) or other safe retreats (Geograpsus) where they ate the cast exuviae and utilized the contained minerals before reemergence. Physiological adaptations for retention of Ca and Mg contribute significantly to storage in Gecarcoidea natalis, allowing retention of 14.2 ± 4.4% Ca and 19.5 ± 7.2% Mg by the soft crab of which 8.5 ± 3.4% and 5.5 ± 2.7%, respectively, were in the gastroliths. In Ocypode cordimana, storage occurred in the hemolymph and digestive gland. Physiological retention of calcium was much lower in Cardisoma hirtipes (4.5 ± 1.36%) and Geograpsus grayi (5.1 ± 2.1%), but all species retained relatively high proportions of their magnesium.

Morphology and ultrastructure of the gills of terrestrial crabs (Crustacea, Gecarcinidae and Grapsidae): Adaptations for air-breathing

The terrestrial crabsGeograpsus grayi, Geograpsus crinipes, Cardisoma hirtipes andGecarcoidea natalis have a reduced number of gills and show a reduced planar gill surface (SA) compared to aquatic species. Gill lamellae are stiffened and thickened (increasing blood/gas (BG) diffusion distances) and nodules maintain wide spacing between lamellae. Haemolymph is directed through the gill lamellae by rows of pillar cells and in the afferent region an intralamellar septum splits the haemolymph into two parallel networks. Gaps in the lines of pillar cells allow movement of haemolymph between adjacent channels. The afferent vessel distributes haemolymph to the lamella via a number of direct channels including the marginal canal and in large gills with the aid of a long, forked sinus which supplies the ventral and central regions of the lamellae. The marginal canal functions in both distribution and collection of haemolymph; the role varies with species. Potential flow-control sites were identified at the junctions between afferent and efferent areas and where the efferent channels enter the efferent branchial vessel. Each gill receives a branch from the sternal artery which supplies all the lamellae. Transport epithelia is the principal cell type in the gills of all species examined though its location varies between species, either being confined to certain gills or specific parts of the lamellae. The gill lamellae of air-breathing crabs are clearly modified to breathe air (stiffening and presence of nodules), though the overall contribution of the gills to gas exchange has been reduced (smaller SA and longer BG diffusion distances). The role of the gills in air-breathing crabs thus appears to have switched from one of an efficient aquatic gas-exchanger (thin with large surface area) and transport tissue, to one that is predominantly set up for ion-regulation.

Sodium Balance and Adaptation to Fresh Water in the Amphibious CrabCardisoma hirtipes

Cardisoma hirtipes can maintain sodium balance in media containing only 0.12 mmol · L⁻¹ Na and survives indefinitely in sodium concentrations of 0.5 mmol · L⁻¹. The crab has a reduced hemolymph concentration and permeability to ions and water compared to marine species, but permeability remains greater than in freshwater crustaceans. The sodium uptake mechanism has a high affinity for sodium ions (Km = 0.264 mmol. L⁻¹) and a moderate Jmax, of 1.67μmol · g⁻¹ · h⁻¹. The rate of transport is doubled in depleted crabs. Sodium loss (1.609 μmol · g⁻¹ · h⁻¹) is 20 times higher than in freshwater decapods, principally because of the high rate of production (8.59% body weight · d⁻¹) of isosmotic urine. The animal lives close to the limit of its ability to regulate sodium in fresh water but is free to leave unsuitably dilute media.