First report of intramolluscan stages of a gorgoderid digenean from a marine bivalve

A survey of bivalves from Heron Island on the Great Barrier Reef, Australia, revealed a novel digenean infection in Lioconcha castrensis (Bivalvia: Veneridae). The cercaria has oral and ventral suckers, a dorsoventrally orientated stylet embedded in the oral sucker, penetration glands, and a large tail that is inflated at its base. This morphology is broadly consistent with that of previously described gorgoderid cercariae. Partial large subunit ribosomal RNA gene (D1-D3 domains) was sequenced and aligned with sequences from other gorgoderids and related families. Phylogenetic analysis also suggests that the species belongs to the Gorgoderinae. To our knowledge, this is the first report of a gorgoderid from a marine bivalve.

The rising tide of ocean diseases: Unsolved problems and research priorities

New studies have detected a rising number of reports of diseases in marine organisms such as corals, molluscs, turtles, mammals, and echinoderms over the past three decades. Despite the increasing disease load, microbiological, molecular, and theoretical tools for managing disease in the world's oceans are underdeveloped. Review of the new developments in the study of these diseases identifies five major unsolved problems and priorities for future research: (1) detecting origins and reservoirs for marine diseases and tracing the flow of some new pathogens from land to sea; (2) documenting the longevity and host range of infectious stages; (3) evaluating the effect of greater taxonomic diversity of marine relative to terrestrial hosts and pathogens; (4) pinpointing the facilitating role of anthropogenic agents as incubators and conveyors of marine pathogens; (5) adapting epidemiological models to analysis of marine disease.

Rare earth element geochemistry of Late Devonian reefal carbonates, canning basin, Western Australia: Confirmation of a seawater REE proxy in ancient limestones

Rare earth element and yttrium (REE+Y) concentrations were determined in 49 Late Devonian reefal carbonates from the Lennard Shelf, Canning Basin, Western Australia. Shale-normalized (SN) REE+Y patterns of the Late Devonian samples display features consistent with the geochemistry of well-oxygenated, shallow seawater. A variety of different ancient limestone components, including microbialites, some skeletal carbonates (stromatoporoids), and cements, record seawater-like REE+Y signatures. Contamination associated with phosphate, Fe-oxides and shale was tested quantitatively, and can be discounted as the source of the REE+Y patterns. Co-occurring carbonate components that presumably precipitated from the same seawater have different relative REE concentrations, but consistent REE+Y patterns. Clean Devonian early marine cements (n = 3) display REE+Y signatures most like that of modern open ocean seawater and the highest Y/Ho ratios (e.g., 59) and greatest light REE (LREE) depletion (average Nd-SN/Yb-SN = 0.413, SD = 0.076). However, synsedimentary cements have the lowest REE concentrations (e.g., 405 ppb). Non-contaminated Devonian microbialite samples containing a mixture of the calcimicrobe Renalcis and micritic thrombolite aggregates in early marine cement (n = 11) have the highest relative REE concentrations of tested carbonates (average total REE = 11.3 ppm). Stromatoporoid skeletons, unlike modern corals, algae and molluscs, also contain well-developed, seawater-like REE patterns. Samples from an estuarine fringing reef have very different REE+Y patterns with LREE enrichment (Nd-SN/Yb-SN > 1), possibly reflecting inclusion of estuarine colloidal material that contained preferentially scavenged LREE from a nearby riverine input source. Hence, Devonian limestones provide a proxy for marine REE geochemistry and allow the differentiation of co-occurring water masses on the ancient Lennard Shelf. Although appropriate partition coefficients for quantification of Devonian seawater REE concentrations from out data are unknown, hypothetical Devonian Canning Basin seawater REE patterns were obtained with coefficients derived from modern natural proxies and experimental values. Resulting Devonian seawater patterns are slightly enriched in LREE compared to most modem seawaters and suggest higher overall REE concentrations, but are very similar to seawaters from regions with high terrigenous inputs. Our results suggest that most limestones should record important aspects of the REE geochemistry of the waters in which they precipitated, provided they are relatively free of terrigenous contamination and major diagenetic alteration from fluids with high, non-seawater-like REE contents. Hence, we expect that many other ancient limestones will serve as seawater REE proxies, and thereby provide information on paleoceanography, paleogeography and geochemical evolution of the oceans. Copyright (C) 2004 Elsevier Ltd.

Developmental expression of two Haliotis asinina hemocyanin isoforms

Hemocyanins are large copper-containing respiratory proteins that play a role in oxygen transport in many molluscs. In some species only one hemocyanin isoform is present while in others two are expressed. The physiological relevance of these isoforms is unclear and the developmental and tissue-specific expression of hemocyanin genes is largely unknown. Here we show that two hemocyanin genes in the gastropod Haliotis asinina, which encode H. asinina hemocyanin (HaH1) and HaH2 isoforms, are developmentally expressed. These genes initially are expressed in a small number of mesenchyme cells at trochophore and pre-torsional veliger stages, with HaH1 expression slightly preceding HaH2. These cells largely are localized to the visceral mass, although a small number of cells are present in head and foot regions. Following metamorphosis the isoforms show overlapping as well as isoform-specific expression profiles, suggesting some degree of isoform-specific function.

Patterns of digenean parasitism of bivalves from the Great Barrier Reef and associated waters

Digenean parasites of marine bivalves are relatively poorly known, particularly in Australia. We surveyed 2256 bivalve individuals ( 47 species, 17 families) from Queensland marine waters incorporating south-east Queensland, Heron Island ( southern Great Barrier Reef) and Lizard Island ( northern Great Barrier Reef). Infections of trematode species from three families, Bucephalidae, Gorgoderidae and Monorchiidae, were found. Overall prevalence of infection was 2.3%. The Bucephalidae was the most commonly found family; 11 species were found in Tellinidae, Ostreidae, Isognomonidae and Spondylidae - the latter two previously unknown as hosts for bucephalids. A single gorgoderid infection was found in a venerid, Lioconcha castrensis. Five species of monorchiids were found from Tellinidae and Lucinidae. All infections are new host/parasite records. No infections were found in 35 of the 47 bivalve species sampled. The generally low prevalence of infection by digeneans of bivalves suggests that it is unlikely that any of the species reported here are seriously damaging to bivalve populations in these waters. We deduce that, at best, we have some life-cycle information but no actual identifications for 10% of the species of trematodes that infect bivalves of Queensland marine waters.

Expressed sequence tag analysis of genes expressed during development of the tropical abalone Haliotis asinina

The tropical abalone. Haliotis asinina. is,in ideal species to investigate the molecular mechanisms that control development. growth, reproduction and shell formation in all cultured haliotids. Here we describe the analysis of 232 expressed sequence tags (EST) obtained front a developmental H. asinina cDNA library intended for future microarray studies. From this data set we identified 183 unique gene Clusters. Of these, 90 clusters showed significant homology with sequences lodged in GenBank, ranging in function from general housekeeping to signal transduction, gene regulation and cell-cell communication. Seventy-one clusters possessed completely novel ORFs greater than 50 codons in length, highlighting the paucity of sequence data from molluscs and other lophotrochozoans. This study of developmental gene expression in H. asinina provides the foundation for further detailed analyses of abalone growth, development and reproduction.

Isolation and characterisation of conomap-Vt, a D-amino acid containing excitatory peptide from the venom of a vermivorous cone snail

Cone snail venom is a rich source of bioactives, in particular small disulfide rich peptides that disrupt synaptic transmission. Here, we report the discovery of conomap-Vt (Conp-Vt), an unusual linear tetradecapeptide isolated from Conus vitulinus venom. The sequence displays no homology to known conopeptides, but displays significant homology to peptides of the MATP (myoactive tetradecapeptide) family, which are important endogenous neuromodulators in molluscs, annelids and insects. Conp-Vt showed potent excitatory activity in several snail isolated tissue preparations. Similar to ACh, repeated doses of Conp-Vt were tachyphylactic. Since nicotinic and muscarinic antagonists failed to block its effect and Conp-Vt desensitised tissue remained responsive to ACh, it appears that Conp-Vt contractions were non-cholinergic in origin. Finally, biochemical studies revealed that Conp-Vt is the first member of the MATP family with a D-amino acid. Interestingly, the isomerization of L-Phe to D-Phe enhanced biological activity, suggesting that this post-translational modified conopeptide may have evolved for prey capture. (c) 2006 Published by Elsevier B.V. on behalf of the Federation of European Biochemical Societies.

Parasitic castration by the digenian trematode Allopodocotyle sp alters gene expression in the brain of the host mollusc Haliotis asinina

Infection of molluscs by digenean trematode parasites typically results in the repression of reproduction - the so-called parasitic castration. This is known to occur by altering the expression of a range of host neuropeptide genes. Here we analyse the expression levels of 10 members of POU, Pax, Sox and Hox transcription factor gene families, along with genes encoding FNIRFamide, prohormone convertase and P-tubulin, in the brain ganglia of actively reproducing (summer), non-reproducing (winter) and infected Haliotis asinina (a vetigastropod mollusc). A number of the regulatory genes are differentially expressed in parasitised H. asinina, but in only a few cases do expression patterns in infected animals match those occurring in animals where reproduction is normally repressed. (c) 2006 Published by Elsevier B.V. on behalf of the Federation of European Biochemical Societies.

Intake rates and the functional response in shorebirds (Charadriiformes) eating macro-invertebrates

As field determinations take much effort, it would be useful to be able to predict easily the coefficients describing the functional response of free-living predators, the function relating food intake rate to the abundance of food organisms in the environment. As a means easily to parameterise an individual-based model of shorebird Charadriiformes populations, we attempted this for shorebirds eating macro-invertebrates. Intake rate is measured as the ash-free dry mass (AFDM) per second of active foraging; i.e. excluding time spent on digestive pauses and other activities, such as preening. The present and previous studies show that the general shape of the functional response in shorebirds eating approximately the same size of prey across the full range of prey density is a decelerating rise to a plateau, thus approximating the Holling type 11 ('disc equation') formulation. But field studies confirmed that the asymptote was not set by handling time, as assumed by the disc equation, because only about half the foraging time was spent in successfully or unsuccessfully attacking and handling prey, the rest being devoted to searching. A review of 30 functional responses showed that intake rate in free-living shorebirds varied independently of prey density over a wide range, with the asymptote being reached at very low prey densities (< 150/m(-2)). Accordingly, most of the many studies of shorebird intake rate have probably been conducted at or near the asymptote of the functional response, suggesting that equations that predict intake rate should also predict the asymptote. A multivariate analysis of 468 'spot' estimates of intake rates from 26 shorebirds identified ten variables, representing prey and shorebird characteristics, that accounted for 81 % of the variance in logarithm-transformed intake rate. But four-variables accounted for almost as much (77.3 %), these being bird size, prey size, whether the bird was an oystercatcher Haematopus ostralegus eating mussels Mytilus edulis, or breeding. The four variable equation under-predicted, on average, the observed 30 estimates of the asymptote by 11.6%, but this discrepancy was reduced to 0.2% when two suspect estimates from one early study in the 1960s were removed. The equation therefore predicted the observed asymptote very successfully in 93 % of cases. We conclude that the asymptote can be reliably predicted from just four easily measured variables. Indeed, if the birds are not breeding and are not oystercatchers eating mussels, reliable predictions can be obtained using just two variables, bird and prey sizes. A multivariate analysis of 23 estimates of the half-asymptote constant suggested they were smaller when prey were small but greater when the birds were large, especially in oystercatchers. The resulting equation could be used to predict the half-asymptote constant, but its predictive power has yet to be tested. As well as predicting the asymptote of the functional response, the equations will enable research workers engaged in many areas of shorebird ecology and behaviour to estimate intake rate without the need for conventional time-consuming field studies, including species for which it has not yet proved possible to measure intake rate in the field.

Parasite communities and diet of Coris Batuensis (Pisces Labridae) from Lizard Island, Great Barrier Reef

Parasite infracommunities of the wrasse Coris batuensis (Bleeker, 1857) were analysed, and the relationship between endoparasites, diet, and host body weight inferred. Thirty-two fish were collected from Lizard Island, Australia. Percentage frequency of occurrence of prey categories in the gut was determined and abundance, prevalence and species richness of parasites were calculated. Fish mainly ate snails, bivalves and crustaceans and this did not vary with body weight. Thirty-one fish were parasitised with at least one of 21 taxa of parasites (4 ectoparasite and 17 endoparasite species), with an average of 4 species and 47 individuals per host. Tetraphyllidean cestode larvae were the most common and abundant group. Parasite life cycles are not known in detail, but small crustaceans, such as copepods and amphipods, are likely to be intermediate hosts for the cestodes, nematodes and digeneans found in C. batuensis. Molluscs, although frequent in the diet, may not be transmitting any parasite species. Numbers of prey and parasite species richness were not correlated. Composition, abundance and species richness of the parasite fauna were similar in hosts with different body weight, corresponding with C. batuensis having a similar diet throughout life. © Queensland Museum.

Dietary selectivity for the toxic cyanobacterium Lyngbya majuscula and resultant growth rates in two species of opisthobranch mollusc

Trophodynamics of blooms of the toxic marine cyanobacterium Lyngkya majuscula were investigated to determine dietary specificity in two putative grazers: the opisthobranch molluscs, Stylocheilus striatus and Bursatella leachii. S. striatus is associated with L. majuscula blooms and is known to sequester L. majuscula metabolites. The dietary specificity and toxicodynamics of B. leachii in relation to L. majuscula is less well documented. In this study we found diet history had no significant effect upon dietary selectivity of S. striatus when offered a range of plant species. However, L. majuscula chemotype may alter S. striatus' selectivity for this cyanobacterium. Daily biomass increases between small and large size groups of both species were recorded in no-choice consumption trials using L. majuscula. Both S. striatus and B. leachii preferentially consumed L. majuscula containing lyngbyatoxin-a. Increase in mass over a 10-day period in B. leachii (915%) was significantly greater than S. striatus (150%), yet S. striatus consumed greater quantities of L. majuscula (g day(-1)) and thus had a lower conversion efficiency (0.038) than B. leachii (0.081) based on sea hare weight per gram of L. majuscula consumed day(-1). Our findings suggest that growth rates and conversion efficiencies may be influenced by sea hare maximum growth potential, acquisition of secondary metabolites or diet type. (C) 2005 Elsevier B.V. All rights reserved.