Preliminary results on the effects of salinity and settling conditions on megalopal metamorphosis of fiddler crab Ilyoplax pusilla

Metamorphosis of fiddler crab Ilyoplax pusilla larvaefrom megalopal to first crab stage wasstudied in laboratory experiments under variousconditions of salinity and substratum. The hatchedzoea metamorphose through five stages before reachingmegalopal stage. The megalops were placed in a 20 mlPetri dishes (2–3 megalops/dish), with salinities of10, 20 or 30 . Each salinity level was tested eitherwith or without sandy mud substratum. Thirty to 35megalops were used in each of the six treatments. Theexperiment was carried out at a water temperature of28 ±0.5°C and with daily feeding of the diatomChaetoceros gracilis. Treatment of 20 salinity andsandy mud substratum revealed the highest metamorphicrate (87%), while in contrast no metamorphosis wasobserved at 30 salinity withoutsandy mud substratum. Duration of the metamorphosiswas about 16 days. Numerous malformed juvenile crabswere observed in treatments conductedwithout sandy mud substratum.     

Hemocyanin-derived phenoloxidase activity with broad temperature stability extending into the cold environment in hemocytes of the hair crab Erimacrus isenbeckii

Phenoloxidase (PO) activity is a major component of the innate immune response in arthropods. In this study, we characterized PO activity from the hair crab Erimacrus isenbeckii, which inhabits very cold regions (2.4-3.4°C) of the Bering Sea. Hemocyte lysate supernatant (HLS) prepared from E. isenbeckii was inactive HLS until activated by nonspecific agents such as sodium dodecyl sulfate and trypsin, and elicitors such as lipopolysaccharide and lipoteichoic acid from the cell wall constituent of bacteria. The PO activity was maximal at 4°C, decreased slightly at temperatures up to 60°C, and fell rapidly at 80°C. Both L-DOPA and catechol were efficient substrates for the PO (EC 1.10.3.1), with K(m) values of 0.96 and 1.15mM, respectively, whereas tyrosine and hydroquinone were not. We isolated a protein fraction from HLS as a hexamer of 75kDa units with 216.7-fold higher PO activity than that of the HLS. The N-terminal amino acid analysis of an isolated protein revealed 80% sequence identity to hemocyanins from other crabs. These results suggest that cold-adapted hemocyanin-derived PO activity is important to the survival of these crabs. This is the first report of a crab PO activity with broad temperature stability extending into the cold environment.     

Distal Retinal Pigment of the Fiddler Crab,Uca pugilator: Release of the Dark-Adapting Hormone by Methionine Enkephalin and FMRFamide

The neuropeptides methionine enkephalin and FMRFamide, when injected into intact fiddler crabs, Uca pugilator, produce dark adaptation of the distal retinal pigment. Furthermore, both neuropeptides stimulate release of distal retinal pigment dark-adapting hormone activity from the isolated eyestalk neuroendocrine complex. It is hypothesized that both neuropeptides, when injected into intact fiddler crabs, act only indirectly on the distal retinal pigment, by stimulating release of this dark-adapting hormone.     

Gill microsomal (Na+,K+)-ATPase from the blue crab Callinectes danae: Interactions at cationic sites

Euryhaline crustaceans tolerate exposure to a wide range of dilute media, using compensatory, ion regulatory mechanisms. However, data on molecular interactions occurring at cationic sites on the crustacean gill (Na⁺,K⁺)-ATPase, a key enzyme in this hyperosmoregulatory process, are unavailable. We report that Na⁺ binding at the activating site leads to cooperative, heterotropic interactions that are insensitive to K⁺. The binding of K⁺ ions to their high affinity sites displaces Na⁺ ions from their sites. The increase in Na⁺ ion concentrations increases heterotropic interactions with the K⁺ ions, with no changes in K_0.5 for K⁺ ion activation at the extracellular sites. Differently from mammalian (Na⁺,K⁺)-ATPases, that from C. danae exhibits additional NH₄⁺ ion binding sites that synergistically activate the enzyme at saturating concentrations of Na⁺ and K⁺ ions. NH₄⁺ binding is cooperative, and heterotropic NH₄⁺ ion interactions are insensitive to Na⁺ ions, but Na⁺ ions displace NH₄⁺ ions from their sites. NH₄⁺ ions also displace Na⁺ ions from their sites. Mg²⁺ ions modulate enzyme stimulation by NH₄⁺ ions, displacing NH₄⁺ ion from its sites. These interactions may modulate NH₄⁺ ion excretion and Na⁺ ion uptake by the gill epithelium in euryhaline crustaceans that confront hyposmotic media.     

The genetic variability of the red king crab, <Emphasis Type="Italic">Paralithodes camtschatica</Emphasis> (Tilesius, 1815) (Anomura,Lithodidae) introduced into the Barents Sea compared with samples from the Bering Sea and Kamchatka region using eleven microsatellite loci

The intentional introduction of red king crab, Paralithodes camtschatica (Tilesius, 1815) in the Barents Sea represent one of a few successful cases and one that now supports a commercial fishery. Introductions of alien species into new environments are often associated with genetic bottlenecks, which cause a reduction in the genetic variation, and this could be important for the spreading potential of the species in the Atlantic Ocean. Red king crab samples collected in the Varangerfjord located on the Barents Sea (northern Norway) were compared with reference crab samples collected from the Bering Sea and Kamchatka regions in the Pacific Ocean. All samples were screened for eleven microsatellite loci, based on the development of species-specific primers. The observed number of alleles per locus was similar, and no reduction in genetic variation, including gene diversity and allelic richness, was detected between the Varangerfjord sample and the reference sample from Okhotsk Sea near Kamchatka, indicating no genetic bottlenecking at least for the microsatellite loci investigated. The same results were found in comparison with the sample from Bering Sea. The level of genetic differentiation among the samples, measured as overall F _ST across all loci, was relatively low (0.0238) with a range of 0.0035–0.1000 for the various loci investigated. The largest pairwise F _ST values were found between the Bering Sea and Varangerfjord/Barents Sea samples, with a value of 0.0194 across all loci tested. The lowest value (0.0101) was found between the Varangerfjord and Kamchatka samples. Genetic differentiation based on exact tests on allele frequencies revealed highly significant differences between all pairwise comparisons. The high level of genetic variation found in the Varangerfjord/Barents Sea sample could be of significance with respect to further spreading of the species to other regions in the North Atlantic Ocean.     

Hemocyte classification and differential counts in the dungeness crab, Cancer magister

The primary purposes of this research were to describe and classify the circulating hemocytes of Cancer magister and devise a method for making differential hemocyte counts for crustaceans. C. magister hemocytes were classified using two simple criteria: the presence or absence of cytoplasmic granules and staining characteristics of the granules, if present. Hyalinocytes (HC) were devoid of granules, intermediate granulocytes (IG) contained basophilic granules or a mixture of basophilic and acidophilic granules, and eosinophilic granulocytes (EG) contained large, acidophilic granules. Hemocyte renewal and a hypothetical maturation sequence of C. magister hemocytes are described and discussed. Differential counts revealed that granulocytes were more abundant than hyalinocytes. For 22 crabs, the mean percentage (and range) of each hemocyte class was: IG, 65.97 (57.50–73.80); EG, 17.76 (4.70–26.47); and HC, 16.25 (3.40–34.67). After additional data are collected and analyzed, the routine use of differential counts may prove to be a valuable method for monitoring the status and health of C. magister and perhaps other crustaceans as well.     

Episodic global dispersal in shallow water marine organisms: the case history of the European shore crabs Carcinus maenas and C. aestuarii

Aim This paper evaluates global collection records, evidence of anthropogenic transport methods, and experimental and distributional data relative to temperature requirements to understand the historical and potential dispersal of a well‐known genus of estuarine crab. Location The records analysed are from temperate and tropical coastal ocean areas. Methods The study is based primarily on literature analysis and examination of museum specimens. Results The human‐mediated successful global dispersal of the European shore crabs Carcinus maenas (Linnaeus, 1758) and C. aestuarii (Nardo, 1847) occurred in three major episodes: around 1800, in the 1850s–70s, and in the 1980s–90s. The nineteenth century introductions occurred through transport by ships (probably in hull fouling or in solid ballast), while the introductions in the 1980s could have occurred through a greater variety of dispersal mechanisms (ships’ hull fouling and seawater system fouling; fouling on semisubmersible drilling platforms; ballast water; transport with fisheries products intended for food or bait; scientific research; releases from aquaria maintained for educational or scientific purposes; or intentional non‐governmental releases for human food production). These introductions have resulted in Carcinus’ establishment in five temperate regions outside of its native Europe in Atlantic North America, Australia, South Africa, Japan and Pacific North America, while releases into tropical regions have not established populations. C. maenas’ range in both its native and introduced regions appears to be regulated by similar temperature parameters, enabling an assessment of its potential distribution. Main conclusions The second episode of Carcinus’ global dispersal, the period from the 1850s to 1870s, may be part of a broader surge of world‐wide invasions caused by an increase in shipping.     

A Mathematical Modelling for the Cheliped Regeneration with Handedness in Fiddler Crab

An enormously developed giant cheliped with the other small one characterizes the adult male fiddler crab. Some experiments with artificial severances of cheliped indicate that such a handedness in the cheliped size is maintained even after the regeneration of severed cheliped. Other experimental researches give some results about an unknown physiological system which controls the emergence and the regeneration of the handedness in the cheliped size. In this paper, with two hypothesized factors relevant to the regeneration of a severed cheliped, we propose a simple mathematical model to describe the experimental result about the cheliped regeneration with a handedness after the cheliped severance for the fiddler crab. Our model gives a suggestion about an underlying system for the cheliped regeneration in the fiddler crab or some other crustacean species.