Land Crab Research Articles

Morphological and molecular identification of two Paragonimus spp., of which metacercariae concurrently found in a land crab, Potamiscus tannanti, collected in Yenbai Province, Vietnam

Paragonimosis is an important food-borne zoonosis especially in Asian countries. Among Paragonimus species, Paragonimus westermani followed by P. skrjabini complex are the major pathogens for human paragonimosis in Asia. In addition, P. heterotremus is an important pathogen in southern China and the Indochina Peninsula and is the only proven species to cause human paragonimosis in Vietnam. During a recent survey in Yenbai Province in northern Vietnam, we found small and large types of Paragonimus metacercariae often concurrently in mountainous crabs, Potamiscus tannanti. Adult worms from those small and large metacercariae were obtained separately by experimental infection in dogs and cats. Morphological and molecular phylogenetic study based on sequences of ITS2 and a part of CO1 genes were performed for the identification of small and large metacercariae and their adults. The results showed that small metacercariae and their adults are completely identical with P. heterotremus in morphology and molecular genetic profiles. In contrast, large metacercariae and their adults have some morphological similarities with P. skrjabini and P. harinasutai, but are unidentifiable from each other by morphology alone. Molecular phylogenetic tree analyses on ITS2 and CO1 genes revealed that large metacercariae and their adults were grouped in the same clade and different from any known Paragonimus species. Although they share the same ancestor with P. skrjabini complex, their genetic distance was considerably different from two other known subspecies, P. skrjabini skrjabini and P. skrjabini miyazakii. Our results provide a new insight on the phylogeny of the genus Paragonimus.

The first record of the land crab, Discoplax rotunda (Quoy & Gaymard, 1824) (Decapoda, Brachyura, Gecarcinidae) from East Africa: the problem of the island species

A mature male Discoplax rotunda (Quoy & Gaymard, 1824) (carapace width 50 mm, length 40 mm) was collected by Mrs. Valentina Vigiani in September 2000, at the edge of the swimming pool of the Reef Hotel, Mombasa, Kenya. The specimen was compared with material from the Aldabra Islands preserved in the Zoological Museum “La Specola”, Florence, Italy, where it has been deposited (MZUF 2611) (fig. 1). Discoplax rotunda is a land crab inhabiting islands in the Indo-West Pacific oceans, from Aldabra and Mauritius to the Ryukyu Islands, Hawaii, and French Polynesia (Turkay, 1974; Yaldwyn & Wodzicki, 1979; Ng & Guinot, 2001). It commonly lives in the supralittoral or in inland habitats. The Gecarcinidae, a circumtropical family, are successful in invading terrestrial habitats, with many species colonizing islands (Turkay, 1974; Hartnoll & Clark, 2006). There are several decapods commonly distributed on Indo-Pacific islands but unknown from continental coasts, such as the coconut crab, Birgus latro (L., 1767) (cf. Burggren & McMahon, 1988), the land hermit crabs, Coenobita perlatus H. Milne Edwards, 1837 and C. brevimanus Dana, 1852 (Anomura, Coenobitidae: Forest, 1954; Haig, 1984; Burggren & McMahon, 1988), the grapsid crabs, Geograpsus crinipes (Dana, 1852), G. grayi (H. Milne Edwards, 1853) (cf. Hartnoll, 1975; Holthuis, 1977), and Metasesarma obesum (Dana, 1851) (cf. Ng & Schubart, 2003). There is no satisfactory explanation for such restricted geographical distribution. The larvae, when released, probably do not migrate nor drift far, and thus settle

Reproduction of the Black Land Crab, Gecarcinus Ruricola, in the San Andres Archipelago, Western Caribbean

Abstract Reproductive biology of the black land crab, Gecarcinus ruricola (Linnaeus, 1758), has been studied in the San Andres Archipelago in the Western Caribbean, on the islands of San Andres and Old Providence. Both sexes become mature at about 50 mm maximum carapace width, and very few specimens below this size take part in the annual breeding migration. In females the ovaries mature progressively from January to April, and laying occurs from May to July. There is no evidence that individual females lay more that once in a year. The breeding migrations were monitored in 2003 and 2004 by recording specimens crossing the coast road (running 50-100 m from the upper shore). On both San Andres and Old Providence migration was limited to specific stretches of the western shores. On both islands migration occurred from late April to July, intensity varying with time. Migration peaks were not consistent between islands or years, and could not be clearly linked to environmental factors. Migrating crabs were mo...

The development of management options for the black land crab ( Gecarcinus ruricola) catchery in the San Andres Archipelago, Colombia

Black land crab ( Gecarcinus ruricola) populations and their dependent catchery in the San Andres Archipelago, Colombia, are under threat from overexploitation, habitat loss and degradation, and road-kill during annual spawning migrations to the sea. This article discusses the participatory approach used to define management of the species and describes the extensive involvement of local communities, particularly catchers and processors, in research and assessment of management options. Many options were considered. General support exists for continued use of closed areas and seasons in species management, in combination with the introduction of a new minimum size limit of 70 mm carapace width. Licensing receives some support, but the use of total allowable catches or quotas is universally rejected. Establishing a legally defined community-driven body, known as the Black Crab Conservation Unit, is seen as a crucial step in the management of the resource and has widespread support.

The Complete Larval Development of Johngarthia Planatus (Brachyura: Grapsoidea: Gecarcinidae) Described from Laboratory Reared Material, with Notes on the Affinity of Gecarcinus and Johngarthia

Abstract The land crab Johngarthia planatus is an eastern tropical Pacific species with a known distribution from Mexico to Colombia. Complete larval development of the species is fully described and illustrated from laboratory-reared material. The five zoeal stages and the megalopa are compared with those of Gecarcinus lateralis lateralis from the Atlantic coast. Main differences for zoeal stages are observed in the carapace and telson lateral spines while minor differences are observed in the mouthparts setation. For the megalopa stage a difference in size of the third maxilliped exopod supports the separation of Johngarthia from Gecarcinus. A brief comparison of all known zoea I and megalopa stages of species of the Gecarcinidae is made, taking into account recent new descriptions.

Molt-inhibiting hormone from the tropical land crab, Gecarcinus lateralis: Cloning, tissue expression, and expression of biologically active recombinant peptide in yeast

Molt-inhibiting hormone (MIH), a member of the crustacean hyperglycemic neuropeptide hormone family, inhibits ecdysteroidogenesis in the molting gland or Y-organ (YO). A cDNA encoding MIH of the land crab (Gel-MIH) was cloned from eyestalk ganglia (EG) by a combination of reverse transcriptase polymerase chain reaction (RT-PCR) and 3′- and 5′-rapid amplification of cDNA ends (RACE). The cDNA (1.4 kb) encoded MIH prohormone containing a 35 amino acid signal peptide and a 78 amino acid mature peptide. The mature peptide had the six cysteines, one glycine, two arginines, one aspartate, one phenylalanine, and one asparagine in identical positions in the highly conserved sequence characteristic of other crustacean MIHs. Gel-MIH was expressed only in the EG, as determined by RT-PCR; it was not detected in Y-organ, heart, integument, gill, testis, ovary, hepatopancreas, thoracic ganglion, or skeletal muscle. A cDNA encoding the mature peptide was used to express recombinant MIH (rMIH) using a yeast ( Pichia pastoris) expression system. Two constructs were designed to yield either a mature MIH fusion protein with a c-myc epitope and histidine (His) tag at the carboxyl terminus or an untagged mature protein without the c-myc and His sequences. Immunoreactive peptides were detected in Western blots of the cell culture media with both MIH constructs, indicating secretion of the processed rMIH into the medium. Culture media containing the untagged mature peptide significantly inhibited ecdysteroid secretion by YOs from land crab and green crab ( Carcinus maenas) cultured in vitro, indicating that the Gel-rMIH was biologically active.

Proteomics and signal transduction in the crustacean molting gland

Regulation of the molting cycle in decapod crustaceans involves 2 endocrine organs: the X-organ/sinus gland (XO/SG) complex located in the eyestalk ganglia and the Y-organ (YO) located in the cephalothorax. Two neuropeptides [molt-inhibiting hormone (MIH) and crustacean hyperglycemic hormone (CHH)] are produced in the XO/SG complex and inhibit ecdysteroidogenesis in the YO. Thus, YO activation is induced by eyestalk ablation (ESA), which removes the primary source of MIH and CHH. Cyclic nucleotides (cAMP and cGMP) and nitric oxide (NO) appear to mediate neuropeptide suppression of the YO. Proteomics was used to identify potential components of signal transduction pathways ("targeted" or cell-map proteomics) as well as assess the magnitude of protein changes in response to activation ("global" or expression proteomics) in the tropical land crab, Gecarcinus lateralis. Total proteins in YOs from intact and ES-ablated animals were separated by two-dimensional gel electrophoresis and expression profiles were assessed by image analysis and gene clustering software. ESA caused a >3-fold increase in the levels of 170 proteins and >3-fold decrease in the levels of 89 proteins; a total of 543 proteins were quantified in total YO extracts. ESA induced significant changes in the levels of 3 groups of proteins eluting from a phosphoprotein column and detected with phosphoprotein staining of two-dimensional gels; ∼17 kDa and ∼150 kDa phosphoproteins increased in activated YOs, while ∼12 kDa phosphoproteins decreased. A ∼150 kDa phosphoprotein, which was isolated only from activated YO, was identified as NO synthase by western blotting and mass spectrometry of trypsin peptides. These data show that phosphorylation of NO synthase is associated with activation of the YO. A neuropeptide signaling pathway involving NO synthase and NO-sensitive guanylyl cyclase is proposed.

A new species of night-heron (Ardeidae: Nyctanassa) from Quaternary deposits on Bermuda

ABSTRACT Nyctanassa carcinocatactes is described from Pleistocene and Holocene cave and pond deposits on the island of Bermuda. It is most similar to the Yellow-crowned Night-Heron N. violacea but differs in having a shorter and much heavier bill, a much more massive cranium, and more robust hindlimbs. Early historical accounts contain descriptions of what is undoubtedly this species, which was presumably exterminated subsequent to human colonization of Bermuda. The cranial and hindlimb specializations of the new species appear to be adaptations for feeding terrestrially on land crabs.

Effects of diet and metamorphosis upon the sterol composition of the butterfly Morpho peleides

Whole body sterol metabolism in insects has seldom been studied. We were able to design an appropriate study at a butterfly farm in Belize. We collected six larvas of butterfly (Morpho peleides), their food (leaves of Pterocarpus bayessii), and their excretions. In addition, six adult butterflies were collected. The sterols of the diet, the larva, and adult butterfly were analyzed by gas-liquid chromatography. The structures of these sterols were identified by digitonin precipitation, GC-MS, and NMR. Four sterols (cholesterol, campesterol, stigmasterol, and sitosterol) and a sterol mixture were found in the food, the body, and the excreta of the larva. The tissue sterol content of the larva was 326 microg. They consumed 276 microg of sterols per day. Their excretion was 185 microg per day as sterols. The total tissue sterol contents of the larva and butterfly were similar, but they had different sterol compositions, which indicated interconversion of sterols during development. There was a progressive increase in the cholesterol content from larva to butterfly and a decrease in the content of sitosterol and other plant sterols, which were likely converted to cholesterol. Our data indicated an active sterol metabolism in butterfly larva. Diet played an important role in determining its sterol composition. During metamorphosis, there was an interconversion of sterols. This is the first paper documenting the fecal sterol excretion in insects as related to dietary intakes.

A pneumo-hydrostatic skeleton in land crabs

Like their aquatic counterparts, terrestrial crabs repeatedly shed their rigid exoskeleton during moulting. But in the case of land crabs, little water is available to provide a temporary hydrostatic skeleton before the new skeleton hardens, and air does not provide the buoyancy necessary to support the animal. Here we show that whenever its exoskeleton is shed, the blackback land crab Gecarcinus lateralis relies on an unconventional type of hydrostatic skeleton that uses both gas and liquid (a 'pneumo-hydrostat'). To our knowledge, this is the first experimental evidence for a locomotor skeleton that depends on a gas. It establishes a new category of hydrostatic skeletal support and possibly a critical adaptation to life on land for the Crustacea.

A mass recruitment event in the land crab Gecarcinus ruricola (Linnaeus, 1758) (Brachyura: Grapsoidea: Gecarcinidae), and a description of the megalop

A mass return to land of the megalop of the land crab Gecarcinus ruricola is reported. The return occurred in June 2004 on the island of Providencia in the western Caribbean: this is the first detailed report of larval return in this species, and the most detailed report for any gecarcinid. Crabs emerged from the sea as megalops over 2 to 3 days, and moved rapidly landwards. Vast numbers migrated > 50 m across land before moulting to the first crab – the megalop is clearly the invasive stage. The megalop is described for the first time, and criteria are identified to discriminate it from other Caribbean gecarcinids. © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society, 2006, 146, 149–164.

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.

Population Biology of the Black Land Crab, Gecarcinus Ruricola, in the San Andres Archipelago, Western Caribbean

Abstract The population biology of the black land crab, Gecarcinus ruricola (Linnaeus, 1758), was studied in the San Andres Archipelago in the western Caribbean. Investigations were conducted on the islands of San Andres (SA), and Old Providence/Santa Catalina (OP). On both islands the mean size differed little between the sexes, but males reached a larger maximum size by ∼5 mm CW. Crabs of both sexes reached greater mean and maximum sizes on OP than on SA (by ∼10 mm CW): this is tentatively attributed to the higher human population and heavier crab exploitation on the latter. The density of crabs was higher on OP than on SA. In natural ‘forest’ habitats it averaged 2174 crabs Ha−1 in the former, and 804 crabs Ha−1 in the latter. On both islands the densities were higher in watersheds adjacent to the coastlines where breeding females migrate to the sea, and to which returning larvae recruit. The total population estimates were about 3 million crabs on OP, and 800,000 on SA. The lower density and populatio...

Postdispersal Fruit and Seed Removal by the CrabGecarcinus lateralisin a Coastal Forest in Veracruz, Mexico1

ABSTRACTIn the coastal semideciduous forest of La Mancha, Veracruz (Mexico), we evaluated the removal of fallen fruits and seeds of different species by the land crabGecarcinus lateralisunder different environmental conditions (age soil of forest stand, topography, and cover). Crabs removed 67 percent of the propagules in the experiments (3106 of a total of 4608), and seeds were removed in greater quantities (61.1%) than fruits (38.9%). Fruits ofMaclura tinctoria(Moraceae) andEhretia tinifolia(Boraginacea) and seeds ofE. tinifoliawere the most affected species. Crabs removed higher quantities of fruits in old‐soil forest and in the understory than in young‐soil forest and gaps. In experiments with seeds, only for the older forest, the crabs removed more seeds in slopes and peaks than in valleys and in the understory than gaps, whereas in the young‐soil forest, the differences were not significant. Our results suggest thatG. lateralis, likeGecarcoidea natalisandGecarcinus quadratus, is an efficient propagule predator and can exert pressure in the establishment of plant species, but in La Mancha, this also depends on site conditions and identity of the species.

Regulation of Blood Pressure in the Land CrabCardisoma guanhumi

We examined the cardiovascular responses to acute and chronic changes in blood volume (BV) in the land crab Cardisoma guanhumi. Acute reduction in BV caused an increase in activity in the dorsoventral muscles (DVMs) and to a lesser extent in the epimeral attractor muscles (EAMs). Contraction of the DVMs and EAMs will decrease the volume of the dorsal sinus and the thorax as a whole, respectively. BV reduction also caused bradycardia with frequent periods of cardiac arrest. There was a small drop in hemolymph pressure. BV expansion had the reciprocal effect on DVM and EAM activity but had no effect on heart rate (fH). After the cardioregulatory nerves were cut, acute hypovolemia had no effect on fH but still caused a moderate increase in DVM activity. After dehydration-induced BV reduction, DVM activity increased, whereas hemolymph pressure, fH, and EAM activity were maintained close to control levels.

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.

Environmental perception of gatherers of the crab 'caranguejo-uçá' (Ucides cordatus, Decapoda, Brachyura) affecting their collection attitudes.

Mangrove forests are productive ecosystems found along the coastal zones of Brazil, providing several profitable resources such as timber, medicinal products, natural dye, fish, crustaceans, and molluscs. For the littoral dwellers of Northeast Brazil, the Brachyura crabs are a major economic resource. The main species they commercialize are the 'goiamum' (Cardisoma guanhumi), 'siris' (Callinectes spp), and the land crab 'caranguejo-uca' (Ucides cordatus). The land crab is the most exploited species, and of most relevance for people living in the surrounding mangrove areas in the State of Paraiba [1-3]. U. cordatus lives in an individual burrow ca. 1 m deep, situated under mangrove trees. Adult crabs have few predators, notably the crab-eating racoon (Procyon cancrivorous), monkeys, and hawks [4]. Despite this, a high predation pressure on U. cordatus is exerted by humans who harvest this species for food [5]. In the Northeast Region of Brazil, the exploitation of U. cordatus holds particular socio-economic importance since it involves many local residents, who benefit from both direct and indirect employment [2,3]. Crab gatherers have observed that the natural stock of U. cordatus has decreased alarmingly since 1998, when an unexpected crab mass-mortality event occurred in the mangrove habitats of the Paraiban littoral [3]. The subsequent low crab abundance created social problems in the surroundings of those mangrove areas and seriously affected the economic welfare of poor people who depend upon crab gathering for their livelihoods. The need for research on the exploitation of mangrove ecosystems and on U. cordatus in particular was emphasized by Maneschy [6], who also suggested the need to study the socio-economics of crab collecting, which has recently experienced an increase in production demand. The life of gatherers is intimately linked to ecological processes and cycles, and their daily involvement with the exploitation of other natural resources will likely help them to develop harvesting strategies for maximizing the crab catch efficiency. An understanding of the ecology of U. cordatus by local gatherers is an important component of the process of exploitation [2,6]. In recent years, researchers have emphasized the importance of traditional knowledge amongst fishermen. They have also emphasized the potential role that traditional fishing practices can play in the development and implementation of sustainable fishery management in the modern world [7-9]. Human communities which rely directly on their natural resources for subsistence, often have a detailed understanding of their local environment [10-12]. The economic, social, and cultural activities of such people often depend upon local environmental goods and services [13]. Ecologists and environmental managers have generally disregarded the possibilities of learning from the traditional human communities [14]. However, a recent acknowledgment of their relevance has led to an intensification of studies on traditional knowledge [14-18]. In Brazil alone, Diegues [19] listed 868 relevant publications on traditional human populations, of which nearly 80% were published over the last 20 years, and mainly in the last decade. Traditional knowledge may help in the establishment of management plans aimed at the sustainable exploitation of natural resources [2,3]. Nordi [20] observed that the government environmental organization controlling the capture of U. cordatus does not consider local human knowledge of the ecology of the species, a fact that possibly explains the poor effectiveness of the regulations governing the exploitation of this resource. U. cordatus individuals are caught manually or by the use of some tools which allow easier access to them. In most of Brazilian States professional crab gatherers are male [21]. During normal harvest procedures gatherers select crabs with respect to both sex and size. In particular, male crabs are preferred due to their higher flesh yield [22]. Gatherers have developed the ability for distinguishing the sex of crabs as inferred from the track the animal leaves close to burrow openings, as well as from the size of burrow entrances. This perception is important since it directly influences the capture process since large male crabs are preferred due to their higher commercial value. The aim of the present work is to evaluate the ability of gatherers to discriminate the sex and size of crabs, and the importance of this ability on the development of successful harvest strategies. It is also intended here to evaluate the implications of this perception for establishing measures aimed at the conservation and management of U. cordatus.

Ecdysteroid-responsive genes, RXR and E75, in the tropical land crab, Gecarcinus lateralis: Differential tissue expression of multiple RXR isoforms generated at three alternative splicing sites in the hinge and ligand-binding domains

In order to study the potential role of the steroid molting hormone (20-hydroxyecdysone) in regulating molt-induced claw muscle atrophy, full-length cDNAs encoding retinoid-X receptor (Gl-RXR) and E75 early ecdysone inducible gene (Gl-E75) were obtained from land crab ( Gecarcinus lateralis) skeletal muscle mRNA using RT-PCR and 3′ and 5′ RACE. Gl-E75A (3528 bp), which encoded a protein of 828 amino acids, had highest sequence identity to Me-E75A from a shrimp ( Metapenaeus ensis). It was expressed in skeletal muscle and gonads. The deduced amino acid sequence of Gl-RXR was highly similar to that of the fiddler crab RXR (Up-RXR) and insect ultraspiracle (USP). Nine variant sequences occurred in Gl-RXR mRNAs at three alternative splicing sites, one in the “T box” in the linker D domain and two in the ligand-binding domain (LBD). The three T-box variants, termed T(+8), T(+7), and T(+12), contained insertions of 8, 7, or 12 amino acids, respectively. Four variants were generated at the first site in the LBD. Two of the LBD site 1 variants differed in the presence (+33) or absence (−33) of a 33-amino acid sequence; the other two were LBD truncations with or without the 33 amino acid sequence (+33ΔE/F and −33ΔE/F, respectively). Two variants differing in the presence (+35) or absence (−35) of a 35-amino acid sequence were generated at the second site in the LBD. The Gl-RXRa isoform (1516 bp) with the longest open reading frame (+12/+33/+35) encoded a protein of 436 amino acids. Thoracic muscle expressed only isoforms with the T(+12) sequence. In contrast, claw muscle expressed isoforms with T(+7) or T(+12) and fewer isoforms with T(+8). Ovary and testis expressed a greater number of RXR isoforms than skeletal muscle. All tissues expressed full-length and truncated RXR isoforms. These data suggest that differences in response of claw and thoracic muscles to elevated ecdysteroid are due in part to differences in the expression of RXR isoforms.

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

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

Three calpains and ecdysone receptor in the land crabGecarcinus lateralis: sequences, expression and effects of elevated ecdysteroid induced by eyestalk ablation

Crustacean muscle has four calpain-like proteinase activities (CDP I, IIa, IIb and III) that are involved in molt-induced claw muscle atrophy, as they degrade myofibrillar proteins in vitro and in situ. Using PCR cloning techniques, three full-length calpain cDNAs (Gl-CalpB, Gl-CalpM and Gl-CalpT) were isolated from limb regenerates of the tropical land crab Gecarcinus lateralis. All three had highly conserved catalytic (dII) and C2-like (dIII) domains. Gl-CalpB was classified as a typical, or EF-hand, calpain, as the deduced amino acid sequence had a calmodulin-like domain IV in the C-terminus and was most similar to Drosophila calpains A and B. Based on its estimated mass (approximately 88.9 kDa) and cross-immunoreactivity with a polyclonal antibody raised against Dm-CalpA, Gl-CalpB may encode CDP IIb, which is a homodimer of a 95-kDa subunit. It was expressed in all tissues examined, including skeletal muscle, heart, integument, gill, digestive gland, hindgut, nerve ganglia, gonads and Y-organ (molting gland). Both Gl-CalpM and Gl-CalpT were classified as atypical, or non-EF-hand, calpains, as they lacked a domain IV sequence. Gl-CalpM was a homolog of Ha-CalpM from lobster, based on similarities in deduced amino acid sequence, estimated mass (approximately 65.2 kDa) and structural organization (both were truncated at the C-terminal end of dIII). It was expressed at varying levels in most tissues, except Y-organ. Gl-CalpT (approximately 74.6 kDa) was similar to TRA-3 in the nematode Caenorhabditis elegans; domain IV was replaced by a unique ;T domain' sequence. It was expressed in most tissues, except eyestalk ganglia and Y-organ. The effects of elevated ecdysteroid, induced by eyestalk ablation, on calpain and ecdysone receptor (Gl-EcR) mRNA levels in skeletal muscles were quantified by real-time PCR. At 1 day after eyestalk ablation, Gl-EcR and Gl-CalpT mRNA levels increased 15- and 19.3-fold, respectively, in claw muscle but not in thoracic muscle. At 3 days after eyestalk ablation, Gl-EcR and Gl-CalpT mRNA levels in claw muscle had decreased to 2.8-fold and 4.3-fold higher than those in intact controls, respectively, suggesting a feedback inhibition by ecdysteroid. There was no significant effect of eyestalk ablation on Gl-CalpB and Gl-CalpM mRNA levels. Gl-CalpT and Gl-EcR mRNA levels were significantly correlated in both claw and thoracic muscles from intact and eyestalk-ablated animals. The data suggest that Gl-CalpT is involved in initiation of claw muscle atrophy by ecdysteroids. Premolt reduction in claw muscle mass and concomitant remodeling of the sarcomere probably result from post-transcriptional regulation of calpains.