Morphological and chemical characterization of mineral concretions in the freshwater bivalveAnodonta cygnea(Unionidae)

Embryonic and Early Larval Development of the Pacific Razor Clam (Siliqua patula)

AbstractThe Pacific razor clam, Siliqua patula (Sugpiaq: Cingtaataq, Dixon, 1789), is vital to commercial, recreational, and subsistence fisheries across the Pacific Northwest Coast of North America. Despite the species' status as one of the most popular shellfish species harvested in the Pacific Northwest, British Columbia, and Alaska, its larval development has never been fully characterized. Generating a developmental times series, and describing development fully, is crucial for guiding targeted management, developing a mariculture strategy for the species, and providing a more pointed avenue for studies examining the response of S. patula to ocean change. This study presents the first photographic documentation of larval development in S. patula, including the timing of key transitions during embryogenesis and early larval development. Scanning electron microscopy revealed that the larval shell forms via a concretion, a process typically documented in early gastropod development. This novel characterization is pertinent, as it conveys the need for the inclusion of alternative bivalve development processes, such as a concretion, in bivalve research. This study also compared development in S. patula to a global assortment of bivalve species, including two other members of the Pharidae family, determining that the timing to D-veliger and trochophore stages was similar to the majority of bivalves surveyed. While bivalve response to climate change is a topic of great interest, not all species of concern have undergone comprehensive developmental assessments, a requisite benchmark for designing climate change studies that examine early life history sensitivity to such changes. This research supports the use of comprehensive developmental studies as prerequisites for designing climate change experimentation, establishes the necessity of high-magnification and high-resolution scanning electron microscopy within developmental assessments, and provides information about the development of a cornerstone bivalve species.

Pathology and infectious agents of unionid mussels: A primer for pathologists in disease surveillance and investigation of mortality events

Freshwater mussels are one of the most imperiled groups of organisms in the world, and more than 30 species have gone extinct in the last century. While habitat alteration and destruction have contributed to the declines, the role of disease in mortality events is unclear. In an effort to involve veterinary pathologists in disease surveillance and the investigation of freshwater mussel mortality events, we provide information on the conservation status of unionids, sample collection and processing techniques, and unique and confounding anatomical and physiological differences. We review the published accounts of pathology and infectious agents described in freshwater mussels including neoplasms, viruses, bacteria, fungi, fungal-like agents, ciliated protists, Aspidogastrea, Digenea, Nematoda, Acari, Diptera, and Odonata. Of the identified infectious agents, a single viral disease, Hyriopsis cumingii plague disease, that occurs only in cultured mussels is known to cause high mortality. Parasites including ciliates, trematodes, nematodes, mites, and insects may decrease host fitness, but are not known to cause mortality. Many of the published reports identify infectious agents at the light or ultrastructural microscopy level with no lesion or molecular characterization. Although metagenomic analyses provide sequence information for infectious agents, studies often fail to link the agents to tissue changes at the light or ultrastructural level or confirm their role in disease. Pathologists can bridge this gap between identification of infectious agents and confirmation of disease, participate in disease surveillance to ensure successful propagation programs necessary to restore decimated populations, and investigate mussel mortality events to document pathology and identify causality.

Review: Antibacterial components of the Bivalve's immune system and the potential of freshwater bivalves as a source of new antibacterial compounds

Antibacterial research is reaching new heights due to the increasing demand for the discovery of new substances capable of inhibiting bacteria, especially to respond to the appearance of more and more multi-resistant strains. Bivalves show enormous potential for the finding of new antibacterial compounds, although for that to be further explored, more research needs to be made regarding the immune system of these organisms. Beyond their primary cellular component responsible for bacterial recognition and destruction, the haemocytes, bivalves have various other antibacterial units dissolved in the haemolymph that intervene in the defense against bacterial infections, from the recognition factors that detect different bacteria to the effector molecules carrying destructive properties. Moreover, to better comprehend the immune system, it is important to understand the different survival strategies that bacteria possess in order to stay alive from the host's defenses. This work reviews the current literature regarding the components that intervene in a bacterial infection, as well as discussing the enormous potential that freshwater bivalves have in the discovery of new antibacterial compounds.

The dark side of soft tissues: Unexpected inorganic carbonate in the invasive slipper limpet Crepidula fornicata and its implications for stable isotope interpretations

RATIONALE

Stable isotopic analysis is extensively used in trophic ecology. Inorganic carbonates, usually originating from shell fragments, are routinely removed from samples using an acid treatment because they affect δ¹³ C values. However, acid treatment can also change δ¹⁵ N values. For some taxa such as molluscs, the general assumption is that acid pre-treatment is not necessary since their shell is easily dissected from soft tissues and represents the only source of inorganic carbonates. However, other sources of non-dietary carbon (e.g., intracellular inorganic carbon) enriched in¹³ C thus get overlooked.

METHODS

Soft tissues (foot) of the invasive gastropod Crepidula fornicata of different size classes were analysed for their δ¹³ C and δ¹⁵ N values with and without acid pre-treatment using isotope ratio mass spectrometry. In toto microscopic investigations coupled with acid treatment, scanning electron microscopy and energy-dispersive spectroscopy were used to highlight the presence of inorganic carbonate. A correction model was derived and applied to existing stable isotope data for C. fornicata. We used both seasonal variations in δ¹³ C signatures and mixing model outputs to assess the error in δ¹³ C values.

RESULTS

Acid pre-treatment had a significant effect on the stable isotope compositions of C. fornicata foot tissue, especially on δ¹³ C values: isotopic differences increased with size, up to 3‰ for large females. No effect was detected for small (below ~20 mm) and motile males. In toto microscopic analysis revealed the presence of small spherules of inorganic carbonate, hence explaining the differences in δ¹³ C values. Mixing model outputs and seasonal variation of δ¹³ C values showed that untreated samples can lead to large misinterpretations about diet proportions and degree of trophic niche overlap, respectively.

CONCLUSIONS

Spherules of inorganic carbonate in C. fornicata soft tissues are likely to be linked with the motility of this species and their mucus production. We recommend assessing the presence of inorganic carbonate in soft tissue of sessile gastropods.

Single and combined effects of Zn, Mn and Fe on the Neotropical freshwater bivalve Anodontites trapesialis: Bioaccumulation and biochemical biomarkers

Important concentrations of Zn, Mn and Fe were detected in a stream near a coal mining area and promoted, in field, biomarkers alterations in the bivalve Anodontites trapesialis. In order to understand the isolated and mixed effects of these metals on these Neotropical bivalves, we run short-term experiments under laboratory controlled conditions. After 96 h-exposure, tissues (gills, mantle, digestive gland, muscle, hemolymph) were removed for metal bioaccumulation analysis, oxidative stress biomarkers (reactive oxygen species (ROS), total antioxidant capacity, lipoperoxidation (LPO), proteins carbonylation (PC), metallothionein (MT), activity of superoxide dismutase and glutathione S-transferase and hemocytes DNA damage) and cholinesterase (ChE versus ASCh activity) activity evaluation. We run three independent tests. In Zn test, clams were exposed to three concentrations of Zn (0.18 mg L^-1, 1.0 mg L^-1, 5.0 mg L^-1); in Mn test, clams were exposed to three concentrations of Mn (0.1 mg L^-1, 0.5 mg L^-1, 5.0 mg L^-1) and in Mix test, clams were exposed to the mixture Zn (1 mg L^-1) + Mn (0.5 mg L^-1), with and without Fe (5.0 mg L^-1). After single exposure to 5.0 mg L^-1, Zn bioaccumulated in all tissues, but only in mantle and hemolymph after exposure to 1.0 mg L^-1. The increased MT in gills of A. trapesialis exposed to Zn appears to be sufficient to avoid damage, since LPO occurred only in digestive glands from animals exposed to 5.0 mg L^-1. We suggested that A. trapesialis had a metabolic suppression in consequence of Mn presence, based on the following results: the decrease of ROS in gills, the decrease of the Zn and Mn concentrations in tissues and the decrease of ChE versus ASCh activity in muscle. Despite this, animals exposed to Mn suffer oxidative damages (LPO and PC) in the mantle and digestive gland and MT increased in the mantle. These results showed A. trapesialis responded differently to each metal and Mn caused more damage. When exposed to Fe, gills level of ROS was increased, despite no changes in metal accumulation occurred. On the other hand, after exposure to the mixtures, tissues bioaccumulated Zn and previously observed damages caused by Mn and Fe disappeared. Consequently, biomarkers were less affected under mixture treatments, demonstrating mixtures effects or responses were not simply a combination of single exposures to Zn, Mn and Fe, but depend on metals toxicokinetics.

Identification of distinct haemocyte populations from the freshwater bivalves swan mussel (Anodonta cygnea) and duck mussel (Anodonta anatina) using wheat-germ agglutinin

Haemocytes play a major role in molluscs immunity. Functional studies are, however, impaired by limited available experimental tools to identify and sort distinct haemocyte populations. Therefore, using nonlethal methods, we aimed at evaluating whether lectin staining combined with flow cytometry could be used to distinguish circulating haemocyte populations from two freshwater bivalves of the family Unionidae, the duck mussel (Anodonta anatina (L., 1758)) and the swan mussel (Anodonta cygnea (L., 1758)). Based on classical classification, haemocytes were distinguished as granulocytes and hyalinocytes and cytological features were visualized using transmission microscopy and staining techniques. Size, granularity, viability, and surface staining using lectins as specific probes were analysed by flow cytometry and fluorescence microscopy. The microscopic proportions of granulocytes and hyalinocytes significantly differed, being of 70% and 30% for A. cygnea and of 85% and 15% for A. anatina, respectively. Two haemocyte populations were sorted by flow cytometry based on size and granularity and confirmed as granulocytes and hyalinocytes. Interestingly, two different granulocyte populations could be further discriminated in A. cygnea according to their binding affinity to wheat-germ agglutinin (WGA), whereas granulocytes of A. anatina all stained similarly. Our results show that WGA labelling combined with flow cytometry can be used to better discriminate Anodonta haemocyte populations and obtain purified populations for functional studies.