Diseases of spiny lobsters: a review

Spiny lobsters have few reported pathogens, parasites and symbionts. However, they do have a diverse fauna comprised of a pathogenic virus, several bacteria, protozoans, helminths and even symbiotic crustaceans. A few idiopathic syndromes have also been reported, but these appear correlated with lobsters held in poor conditions. Fungal and bacterial pathogens present significant threats for rearing spiny lobsters in aquaculture settings, but only one pathogen, Panulirus argus virus 1, is thought to have damaged a fishery for a spiny lobster. No doubt others will emerge as lobsters are brought into aquaculture setting and as fishing pressure intensifies with stocks become more susceptible to anthropogenic stressors.     

Comparison of genetic and morphological methods to detect the presence of American lobsters, <Emphasis Type="Italic">Homarus americanus</Emphasis> H. Milne Edwards, 1837 (Astacidea: Nephropidae) in Norwegian waters

American lobsters (Homarus americanus H. Milne Edwards, 1837) are imported live to Europe and should according regulations be kept in land-based tanks until sold. In spite of the strict regulations aimed specifically at preventing the introduction of this species into the NE Atlantic, several specimens of H. americanus have been captured in the wild, especially in Oslofjord, Norway since 1999. One of the great concerns is interbreeding between the introduced American species and the local European lobster, H. gammarus (Linnaeus, 1758). For this reason an awareness campaign was launched in 2000 focusing on morphologically “unusual” lobsters caught in local waters. Morphological characters have been based on colour and sub-ventral spines on the rostrum. Two samples of H. americanus were used for comparisons, as well as samples of European lobster from Oslofjord collected in 1992. Previous genetic analyses (allozymes, mtDNA and microsatellite DNA) have demonstrated that the American lobster is distinct from its European counterpart, with several additional alleles at many loci in addition to different allelic frequency distribution of alleles of “shared” alleles. During the present study, thirteen microsatellite loci were tested in the initial screening, and the three most discriminating loci (Hgam98, Hgam197b and Hgam47b) were used in a detailed comparison between the two species. A total of 45 unusual lobsters were reported captured from Ålesund (west) to Oslofjord (southeast) from 2001 to 2005 and these were analysed for the three microsatellite loci. Nine specimens were identified as American lobsters. Comparisons between morphological and genetic characteristics revealed that morphological differences are not reliable in discrimination the two species, or to identify hybrids. Further, some loci display almost no overlapping in allele frequency distribution for the reference samples analysed, thus providing a reliable tool to identify hybrids.     

Comparing integrated stable isotope and eddy covariance estimates of water-use efficiency on a Mediterranean successional sequence

Young larval stages of many organisms represent bottlenecks in the life-history of many species. The high mortality commonly observed in, for example, decapod larvae has often been linked to poor nutrition, with most studies focussing on food quantity. Here, we focus instead on the effects of quality and have investigated its effects on the nutritional condition of lobster larvae. We established a tri-trophic food chain consisting of the cryptophyte Rhodomonas salina, the calanoid copepod Acartia tonsa and larvae of the European lobster Homarus gammarus. In a set of experiments, we manipulated the C:N:P stoichiometry of the primary producers, and accordingly those of the primary consumer. In a first experiment, R. salina was grown under N- and P-limitation and the nutrient content of the algae was manipulated by addition of the limiting nutrient to create a food quality gradient. In a second experiment, the effect on lobster larvae of long- and short-term exposure to food of varying quality during ontogenetic development was investigated. The condition of the lobster larvae was negatively affected even by subtle N- and P-nutrient limitations of the algae. Furthermore, younger lobster larvae were more vulnerable to nutrient limitation than older ones, suggesting an ontogenetic shift in the capacity of lobster larvae to cope with low quality food. The results presented here might have substantial consequences for the survival of lobster larvae in the field, as, in the light of future climate change and re-oligotrophication of the North Sea, lobster larvae might face marked changes in temperature and nutrient conditions, thus significantly altering their condition and growth.     

Myospora metanephrops (n. g., n. sp.) from marine lobsters and a proposal for erection of a new order and family (Crustaceacida; Myosporidae) in the Class Marinosporidia (Phylum Microsporidia)

In this study we describe, the first microsporidian parasite from nephropid lobsters. Metanephrops challengeri were captured from an important marine fishery situated off the south coast of New Zealand. Infected lobsters displayed an unusual external appearance and were lethargic. Histology was used to demonstrate replacement of skeletal and other muscles by merogonic and sporogonic stages of the parasite, while transmission electron microscopy revealed the presence of diplokaryotic meronts, sporonts, sporoblasts and spore stages, all in direct contact with the host sarcoplasm. Analysis of the ssrDNA gene sequence from the lobster microsporidian suggested a close affinity with Thelohania butleri, a morphologically dissimilar microsporidian from marine shrimps. Whilst morphological features of the lobster parasite are consistent with members of the family Nosematidae, molecular data place the parasite closer to members of the family Thelohanidae. Due to the contradiction between morphological and molecular taxonomic data, we propose the erection of a new genus in which the lobster parasite is the type species (Myospora metanephrops). Furthermore, we recommend the erection of a new family (Myosporidae) and a new order (Crustaceacida) to contain this genus. The taxonomic framework presented could be further applied to the re-classification of existing members of the Phylum Microsporidia.     

Neuromuscular synapses on the dactyl opener muscle of the lobster Homarus americanus

The crustacean dactyl opener neuromuscular system has been studied extensively as a model system that exhibits several forms of synaptic plasticity. We report the ultrastructural features of the synapses on dactyl opener of the lobster (Homarus americanus) as determined by examination of serial thin sections. Several innervation sites supplied by an inhibitory motoneuron have been observed without nearby excitatory innervation, indicating that excitatory and inhibitory inputs to the muscle are not always closely matched. The ultrastructural features of the lobster synapses are generally similar to those described previously for the homologous crayfish muscle, with one major distinction: few dense bars are seen at the presynaptic membranes of these lobster synapses. The majority of the lobster neuromuscular synapses lack dense bars altogether, and the mean number of dense bars per synapse is relatively low. In view of the finding that the physiology of the lobster dactyl opener synapses is similar to that reported for crayfish, these ultrastructural observations suggest that the structural complexity of the synapses may not be a critical factor determining synaptic plasticity.This work was supported by funds from the University of Virginia Research and Development Committee.     

Implication of an environmentally induced hamartoma in commercial shrimps

An overgrowth of muscle protruded through the ventral portion of the sixth abdominal segment of Penaeus aztecus and P. setiferus. This hamartoma was observed in 33 postlarval shrimp and is the first reported from a crustacean. Even though afflicted individuals represented a small proportion of the shrimp examined, nearly all such individuals were collected from the presumed most heavily polluted site. We suggest an unidentified pollutant as the cause of the abnormality.     

Population genomic evidence that human and animal infections in Africa come from the same populations of Dracunculus medinensis

BackgroundGuinea worm–Dracunculus medinensis–was historically one of the major parasites of humans and has been known since antiquity. Now, Guinea worm is on the brink of eradication, as efforts to interrupt transmission have reduced the annual burden of disease from millions of infections per year in the 1980s to only 54 human cases reported globally in 2019. Despite the enormous success of eradication efforts to date, one complication has arisen. Over the last few years, hundreds of dogs have been found infected with this previously apparently anthroponotic parasite, almost all in Chad. Moreover, the relative numbers of infections in humans and dogs suggests that dogs are currently the principal reservoir on infection and key to maintaining transmission in that country.Principal findingsIn an effort to shed light on this peculiar epidemiology of Guinea worm in Chad, we have sequenced and compared the genomes of worms from dog, human and other animal infections. Confirming previous work with other molecular markers, we show that all of these worms are D. medinensis, and that the same population of worms are causing both infections, can confirm the suspected transmission between host species and detect signs of a population bottleneck due to the eradication efforts. The diversity of worms in Chad appears to exclude the possibility that there were no, or very few, worms present in the country during a 10-year absence of reported cases.ConclusionsThis work reinforces the importance of adequate surveillance of both human and dog populations in the Guinea worm eradication campaign and suggests that control programs aiming to interrupt disease transmission should stay aware of the possible emergence of unusual epidemiology as pathogens approach elimination.     

Biomedical applications of nisin

Nisin is a bacteriocin produced by a group of Gram‐positive bacteria that belongs to Lactococcus and Streptococcus species. Nisin is classified as a Type A (I) lantibiotic that is synthesized from mRNA and the translated peptide contains several unusual amino acids due to post‐translational modifications. Over the past few decades, nisin has been used widely as a food biopreservative. Since then, many natural and genetically modified variants of nisin have been identified and studied for their unique antimicrobial properties. Nisin is FDA approved and generally regarded as a safe peptide with recognized potential for clinical use. Over the past two decades the application of nisin has been extended to biomedical fields. Studies have reported that nisin can prevent the growth of drug‐resistant bacterial strains, such as methicillin‐resistant Staphylococcus aureus, Streptococcus pneumoniae, Enterococci and Clostridium difficile. Nisin has now been shown to have antimicrobial activity against both Gram‐positive and Gram‐negative disease‐associated pathogens. Nisin has been reported to have anti‐biofilm properties and can work synergistically in combination with conventional therapeutic drugs. In addition, like host‐defence peptides, nisin may activate the adaptive immune response and have an immunomodulatory role. Increasing evidence indicates that nisin can influence the growth of tumours and exhibit selective cytotoxicity towards cancer cells. Collectively, the application of nisin has advanced beyond its role as a food biopreservative. Thus, this review will describe and compare studies on nisin and provide insight into its future biomedical applications.     

Multiple lobster tubulin isoforms are encoded by a simple gene family

Microtubule proteins isolated from pleopod tegumental gland (PTG) tissue of the American lobster, Homarus americanus, reveal a complex tubulin (Tub) profile. To determine whether Tub heterogeneity in PTG is due to expression of a large tub gene family or the result of post-translational modification, a PTG cDNA library was constructed. Clones coding for both α- and β-Tub were isolated, sequenced and found to contain open reading frames (ORFs) of 451 amino acids (aa). Alignments reveal phylogenetic clustering with other arthropods and identify unique changes in primary structure which may have functional significance. These clones, when used to probe restriction enzyme-digested lobster genomic DNA in transfer-hybridization experiments, revealed a simple banding pattern indicating a lobster tub gene family of limited complexity. Lobsters appear to make use of a small tub gene family and fulfill the varied functional requirements imposed upon cellular microtubules through post-translational modifications of relatively few gene products.     

Influence of lunar cycle on catches of spiny lobster Panulirus argus (Decapoda: Palinuridae) in the Gulf of Batabanó, Cuba

Many biological processes such as reproductive and migratory behaviours have been associated with moon cycles. In this study, the nocturnal light levels associated with lunar cycle (INT) were correlated with daily catch rate of lobster P. argus, during seven lunar months of 2002 fishing period, to determine a possible relationship between these variables. The lobster catches were obtained from three fishing companies that develop their activities in the Gulf of Batabanó: EPICOL that fishes in Coloma area; PESCAHABANA in Batabanó area and PESCAISLA in Isla area. Daily catch per boat (CDB) was used as a measurement of daily catch variations (catch rate). The correlation was analyzed showing it in chronological graphs based on average of CDB per lunar phases, comparing lobster catch rate per lunar phases -with the Kruskal-Wallis test-. Spearman rank correlation coefficient and cross correlation techniques were also applied. Similarities between lobster catch rate and the lunar cycle were not found. Spearman rank correlation coefficient was modularly smaller than 0.1 in all cases and demonstrated quantitatively that correlation between CDB and INT does not exist. Kruskal-Wallis test detected differences only in Batabanó area but not when making the analyses for the whole Gulf of Batabanó. Finally, the cross correlations do not detected significance in any zone, as well. It is concluded that, in opposition to what other authors have reported, the catch rates of P. argus and the lunar cycle did not show significant correlation in the Gulf of Batabanó. This trend was independent of the fishing art, which varied according to the time of the year that was analyzed.     

Behavioral Immunity Suppresses an Epizootic in Caribbean Spiny Lobsters

Sociality has evolved in a wide range of animal taxa but infectious diseases spread rapidly in populations of aggregated individuals, potentially negating the advantages of their social interactions. To disengage from the coevolutionary struggle with pathogens, some hosts have evolved various forms of “behavioral immunity”; yet, the effectiveness of such behaviors in controlling epizootics in the wild is untested. Here we show how one form of behavioral immunity (i.e., the aversion of diseased conspecifics) practiced by Caribbean spiny lobsters (Panulirus argus) when subject to the socially transmitted PaV1 virus, appears to have prevented an epizootic over a large seascape. We capitalized on a "natural experiment" in which a die-off of sponges in the Florida Keys (USA) resulted in a loss of shelters for juvenile lobsters over a ~2500km² region. Lobsters were thus concentrated in the few remaining shelters, presumably increasing their exposure to the contagious virus. Despite this spatial reorganization of the population, viral prevalence in lobsters remained unchanged after the sponge die-off and for years thereafter. A field experiment in which we introduced either a healthy or PaV1-infected lobster into lobster aggregations in natural dens confirmed that spiny lobsters practice behavioral immunity. Healthy lobsters vacated dens occupied by PaV1-infected lobsters despite the scarcity of alternative shelters and the higher risk of predation they faced when searching for a new den. Simulations from a spatially-explicit, individual-based model confirmed our empirical results, demonstrating the efficacy of behavioral immunity in preventing epizootics in this system.     

First records of the powdery mildews <Emphasis Type="Italic">Erysiphe platani</Emphasis> and <Emphasis Type="Italic">E. alphitoides</Emphasis> on <Emphasis Type="Italic">Ailanthus altissima</Emphasis> reveal host jumps independent of host phylogeny

The tree-of-heaven Ailanthus altissima (family Simaroubaceae, order Sapindales) is one of the most invasive neophytes in Europe. The tree originated in China and became invasive worldwide in areas with Mediterranean to temperate climates. As known from other invasive plants, only a few pathogens have been reported from A. altissima in Europe, and, to date, powdery mildews on it have been unknown in the European region. Recently, two powdery mildews were found on A. altissima during a survey of neomycetes on non-native plants in Switzerland. Because they did not fit with any of the species known to occur on Simaroubaceae in Asia, they were identified by DNA barcoding using sequences of the ITS region of the n-rDNA, revealing them to be the powdery mildews of plane and oak trees, Erysiphe platani and E. alphitoides. This is the first record of E. platani on a host outside the genus Platanus and its family Platanaceae, as well as its order Proteales. In contrast, E. alphitoides has been reported to occur on several host families and orders. Host jumps over great phylogenetic distances—such as across plant families and orders—appear to be quite common in biogeographically novel associations between Erysiphales species and plants. The consequences of such host jumps for identity and taxonomic placement of species are discussed here. It is further questioned whether both pathogens are usable as biological control agents against the tree-of-heaven.     

In Vitro Antibacterial Mechanism of Action of Crude Garlic (Allium sativum) Clove Extract on Selected Probiotic Bifidobacterium Species as Revealed by SEM,TEM, and SDS-PAGE Analysis

There has been much research on the effects of garlic (Allium sativum) on numerous pathogens, but very few, if any, studies on its effect on beneficial, probiotic bifidobacteria. We have recently shown that garlic exhibits antibacterial activity against bifidobacteria. The mechanism by which garlic kills bifidobacteria is yet to be elucidated. This study sought to determine the mechanism of action of garlic clove extract on selected Bifidobacterium species using scanning and transmission electron microscopy and SDS-PAGE analysis. SEM micrographs revealed unusual morphological changes such as cell elongation, cocci-shaped cells with cross-walls, and distorted cells with bulbous ends. With TEM, observed changes included among others, condensation of cytoplasmic material, disintegration of membranes, and loss of structural integrity. SDS-PAGE analysis did not reveal any differences in whole-cell protein profiles of untreated and garlic clove extract-treated cells. The current study is the first to reveal the mechanism of action of garlic clove extract on probiotic Bifidobacterium species. The results indicate that garlic affects these beneficial bacteria in a manner similar to that exhibited in pathogens. These results therefore further highlight that caution should be taken especially when using raw garlic and probiotic bifidobacteria simultaneously as viability of these bacteria could be reduced by allicin released upon crushing of garlic cloves, thereby limiting the health benefits that the consumer anticipate to gain from probiotics.     

The occurrence of inflammatory granulomas in the ctenidial marsupium of Corbicula fluminea (mollusca: Bivalvia): A consequence of larval incubation

A number of tumor-like cysts in the ctenidia of the freshwater bivalve Corbicula fluminea are described. The cysts result from the encapsulation of incubated larvae within the female inner demibranchs which are modified to form a marsupium. Corbicula fluminea is a protandric consecutive hermaphrodite, and larval incubation commences with sex reversal and the release of the first eggs. For some reason a few of the larvae are not released, and their retention and subsequent death results in the mobilization of the innate cellular defensive mechanism of the parent. This process involves, initially, an invasion of epithelioid cells and amoebocytes (granulocytes), resulting in hyperplasia. This is followed by structural changes to the epithelium bordering the interlamellar spaces (within which the larvae are incubated) to form ultimately the cyst wall. The epithelium is surrounded externally by layers of fibrocytes which eventually form a thick capsule. The autolyzed larval tissues are themselves invaded by fibrocytes, epithelioid cells, and amoebocytes and, in one specimen, had formed a three-layered capsule within the surrounding capsule. The amoebocytes probably reabsorb the larval cellular debris. This unusual example of a molluscan cellular defensive mechanism may assist in the diagnosis and separation of hyperplastic injury responses from neoplasmic conditions in invertebrates.     

Use of Herring Bait to Farm Lobsters in the Gulf of Maine

Background

Ecologists, fisheries scientists, and coastal managers have all called for an ecosystem approach to fisheries management, yet many species such as the American lobster (Homarus americanus) are still largely managed individually. One hypothesis that has yet to be tested suggests that human augmentation of lobster diets via the use of Atlantic herring (Clupea harengus) as bait may contribute to recent increases in lobster landings. Currently 70% of Atlantic herring landings in the Gulf of Maine are used as bait to catch lobsters in traps throughout coastal New England.

Methodology/Principal Findings

We examined the effects of this herring bait on the diet composition and growth rate of lobsters at heavily baited vs. seasonally closed (i.e., bait free) sites in coastal Maine. Our results suggest that human use of herring bait may be subsidizing juvenile lobster diets, thereby enhancing lobster growth and the overall economic value and yield of one of the most valuable fisheries in the U.S.

Conclusions/Significance

Our study illustrates that shifting to an ecosystem approach to fisheries management should require consideration of cross-fishery interactions.