Distribution,abundance and shell morphology of Littorina saxatilis (Olivi) and Littorina arcana Hannaford Ellis at Robin Hood's Bay,North Yorkshire

Preliminary investigations on the occurrence of molluscs and waterfowl at the man-made Lake Zegrzyskie were begun in 1986.The numbers, biomass and dominance structure of molluscs were analysed at different stations in the Lake. Some mollusc species were observed in huge numbers. Waterfowl, especially benthivorous species, were found in big flocks all the year round, but reached highest numbers in autumn. The possible effects of predation pressure from waterfowl on mollusc communities were analysed.     

NADPH-diaphorase activity in the digestive system of gastropod molluscs <Emphasis Type="Italic">Achatina fulica</Emphasis> and <Emphasis Type="Italic">Littorina littorea</Emphasis>

Distribution and morphological peculiarities of nitroxidergic elements throughout the entire length of digestive tract was studied for the first time in gastropod molluscs Littorina littorea (Prosobranchia) and Achatina fulica (Pulmonata) using histochemical detection of NADPH-diaphorase (NADPHd). NO-ergic cells and fibers were revealed in all parts of the mollusc digestive system beginning from esophagus. Intensive NADPHd activity is found in a great number of intraepithelial cells of the open type and their processes in the intraand subepithelial nerve plexuses, subepithelial neurons, granular connective tissue cells, and multiple nervous fibers distributed among muscular elements of digestive tract as well as those in nerves innervating the tract. NADPHd was also revealed in receptor cells in the oral area and in the A. fulica CNS ganglia innervating the digestive tract. A. fulica has a more complicated organization of A. fulica nitroxidergic system of the digestive tract. A system of glomerular structures formed by thin NADPHd-positive neural fibers coming from epithelium is found directly beneath the epithelium in esophagus, stomach, and midgut of the mollusc. More superficially under the main groups of muscular elements there are revealed small clusters of NADPHd-positive neurons that can be classified as primitive, non-structured microganglia. The distribution pattern and a possible functional role of nitroxidergic elements in digestive tract of molluscs as compared with other invertebrate and vertebrate animals are discussed.     

The influence of season and the tidal cycle on division of labour by the radula during feeding in the estuarine brooding gastropod <Emphasis Type="Italic">Crepipatella dilatata</Emphasis> (Calyptraeidae)

The brooding gastropod Crepipatella dilatata can feed by scraping the substrate with the radula and by suspension-feeding, which also requires use of the radula. There is a “division of labour” for the radula among three discrete tasks associated with feeding: (1) removing mucous balls from the food pouch; (2) transferring the mucous cord from the neck channel to the mouth (both components of suspension-feeding); (3) scraping the substrate. We hypothesised that the proportion of time used for each feeding activity varies according to environmental conditions. Total radular activity in females was greatest at high tide and in summer. The rate of radular extrusion for ingesting the mucous cord varied seasonally and between brooding and non-brooding females. Non-brooding females exhibited higher rates of radular extrusion for ingesting the mucous cord and for scraping the substrate than did brooders. In females, radular activity in removing the mucous ball from the food pouch was strongly influenced by the tidal cycle during winter, reaching minimum values at low tide. Differences were recorded in substrate scraping among seasons and within tidal cycles, and among males, brooding females and non-brooding females. Brooding females displayed less rasping than non-brooders, since the area available for grazing was restricted by the egg mass. Throughout the year, including low salinity periods, males allocated a greater proportion of total radular activity to rasping than to removing the mucous ball or ingesting the mucous cord. The feeding behaviour of both males and females is modulated by salinity, but the principal determinants of radular activity are the mode of reproduction (brooding in females) and, in males, motility.     

Non-Indigenous Species and Ecological Explanation

Within the last 20 years, the US has mounted amassive campaign against invasions bynon-indigenous species (NIS) such as zebramussels, kudzu, water hyacinths, and brown treesnakes. NIS have disrupted native ecosystemsand caused hundreds of billions of dollars ofannual damage. Many in the scientificcommunity say the problem of NIS is primarilypolitical and economic: getting governments toregulate powerful vested interests thatintroduce species through such vehicles asships' ballast water. This paper argues that,although politics and economics play a role,the problem is primarily one of scientificmethod. Even if commercial interests werewilling to spend the necessary funds to controlNIS, and even if government were willing toregulate them, ecological theory is notadequate to provide clear direction for eithereffort. The paper argues there is nocomprehensive, predictive theory ofinvasibility, as part of a larger theory ofcommunity structure, that might guideecological decision making regarding NIS, andfor at least three reasons. (1) There is nofirm definition of NIS, native, exotic,and so on, and ecologists do not use the termsconsistently; as a result, biologists debatingvarious accounts of community structure andecological explanation often do not even makelogical contact with each other. (2) Thedominant theory used to understandinvasibility, island biogeography, has noprecise predictive power and is unable toclarify when NIS might promote biodiversity andwhen they might hinder it. (3) There are nofirm, empirical generalizations that revealwhen a colonizer or a NIS might be likely totake over a new environment, and when it mightnot succeed in doing so. As a result,scientists have only rough rules of thumb toshore up their arguments against NIS. Given theincompleteness of current ecological theory,the paper closes with several suggestions forways that study of NIS might enhanceunderstanding of basic commmunity structuresand vice versa.     

Evolutionary radiation of cytotoxic effects in bivalve and gastropod haemolymph

A comparative immunological survey of cytotoxic properties of whole and cell-free haemolymph (plasma) was performed on four species of marine molluscs. Diverse target cells were used: auto- and heterologous mollusc haemocytes, starfish Asterias rubens coelomocytes, trematode Himasthla elongata rediae, and human erythrocytes. While all the four mollusc species were found to contain cytotoxic factors in their plasma, functional features of these molecules in bivalve and gastropod species are essentially different. Cell-free haemolymph of two clams, Mya arenaria and Mytilus edulis, contains pre-synthetized cytolytic complexes capable of immediate and generalized activation, leading to destruction of a broad range of target cells. On the contrary, two gastropod species, Buccinum undatum and Littorina littorea, possess haemolytic factors which display high specificity of recognition of receptor molecules on the target cells and slow cytolytic reaction. Overall, molecular strategies of cytolytic cascade activation in Bivalvia and Gastropoda can be described as low- and highly selective, respectively.     

The Diversity of Strategies of Defense from Pathogens in Molluscs

Based on our own results and literature data, a comparative analysis is performed of particularities of mechanisms of defense from pathogens in representatives of Bivalvia and Gastropoda. The agglutinating and opsonizing activities of plasma from molluscs of phylogenetically distant species were revealed to differ significantly. These differences may be described in terms of two contrast strategies: low-promiscuous that is more typical of most gastropod mollusc species, it is characterized by a narrow specificity of plasma agglutinins and a strong dependence of phagocytosis on the presence of plasma proteins in the medium; the high-promiscuous strategy is characteristic predominately of bivalve molluscs whose plasma agglutinins are able to react with a wider spectrum of indicator cells, and the rate of phagocytosis in this case does not depend on the presence of plasma proteins in the medium. The diversity of strategies of defense from pathogens can explain differences in spectra of pathogen organisms parasitizing in Gastropoda and Bivalvia.     

Learning of apple fruit biotypes by apple maggot flies

Previously, we showed that after a female apple maggot fly, Rhagoletis pomonella,arrives on a host hawthorn or apple fruit, its propensity to accept (bore into) or reject that fruit prior to egg deposition can be modified by previous ovipositional experience with one or the other species and, hence, involves learning. Here, we present both field and laboratory evidence indicating that females also are able to learn characteristics of three different apple biotypes or cultivars: Early Macintosh, Red Delicious, and Golden Delicious. We suspect that females learn to discriminate among these three cultivars on the basis of differences in chemical stimuli among cultivars. The effect of fruit cultivar learning was not as strong as the effect of fruit species learning.     

Large-Scale Trade in Legally Protected Marine Mollusc Shells from Java and Bali,Indonesia

Background

Tropical marine molluscs are traded globally. Larger species with slow life histories are under threat from over-exploitation. We report on the trade in protected marine mollusc shells in and from Java and Bali, Indonesia. Since 1987 twelve species of marine molluscs are protected under Indonesian law to shield them from overexploitation. Despite this protection they are traded openly in large volumes.

Methodology/Principal Findings

We collected data on species composition, origins, volumes and prices at two large open markets (2013), collected data from wholesale traders (2013), and compiled seizure data by the Indonesian authorities (2008–2013). All twelve protected species were observed in trade. Smaller species were traded for <USD1.00 whereas prices of larger species were USD15.00–40.00 with clear price-size relationships. Some shells were collected locally in Java and Bali, but the trade involves networks stretching hundreds of kilometres throughout Indonesia. Wholesale traders offer protected marine mollusc shells for the export market by the container or by the metric ton. Data from 20 confiscated shipments show an on-going trade in these molluscs. Over 42,000 shells were seized over a 5-year period, with a retail value of USD700,000 within Indonesia; horned helmet (Cassis cornuta) (>32,000 shells valued at USD500,000), chambered nautilus (Nautilus pompilius) (>3,000 shells, USD60,000) and giant clams (Tridacna spp.) (>2,000 shells, USD45,000) were traded in largest volumes. Two-thirds of this trade was destined for international markets, including in the USA and Asia-Pacific region.

Conclusions/Significance

We demonstrated that the trade in protected marine mollusc shells in Indonesia is not controlled nor monitored, that it involves large volumes, and that networks of shell collectors, traders, middlemen and exporters span the globe. This impedes protection of these species on the ground and calls into question the effectiveness of protected species management in Indonesia; solutions are unlikely to be found only in Indonesia and must involve the cooperation of importing countries.     

Facies and fauna of the Pennsylvanian Buckhorn Asphalt Quarry deposit: a review and new data on an important Palaeozoic fossil <Emphasis Type="Italic">Lagerstätte</Emphasis> with aragonite preservation

The Pennsylvanian Buckhorn Asphalt Quarry contains the best-preserved Palaeozoic mollusc fauna in the world. Early impregnation of mixed siliciclastic–carbonate rocks (mudstones, pack to grainstones, shell beds, and conglomerates) with hydrocarbons prevented aragonite destruction (“Impregnation Fossil Lagerstätte”). The exceptional preservation comprises shell microstructures, microornaments and early ontogenetic shells. Most gastropods had planktotrophic larval development indicating a high primary production although the remains of phytoplankton are very rare in this and other Late Palaeozoic deposits. Deposition occurred close to a shallow-water coastal area. Mass flow processes (density currents) triggered by storms were involved in the transport mechanisms of some units. Shells of benthic molluscs yield the most diverse known Palaeozoic microboring assemblage, indicating at least partly euphotic conditions. The invertebrate fauna comprises about 160 species and is dominated by molluscs, which is unusual for a Palaeozoic deposit, suggesting that aragonite dissolution produces a major bias in the fossil record. However, most mollusc genera in the Buckhorn deposit are also known from other Pennsylvanian occurrences as recrystallised shells. This shows that preservation bias via preferential aragonite dissolution may be overestimated.     

Effects of temperature stress on NO-synthase and tyrosine hydroxylase activities in the central nervous system of bivalve molluscs

Effects of temperature stress on activities of NO-synthase (NOS) and tyrosine hydroxylase (TH) in the CNS of two species of bivalve molluscs, Mizuchopecten yessoensis and Chlamys farreri nipponensis (Pectinidae) were studied using NADPH-diaphorase histochemistry and immunocytochemistry. General and specific peculiarities in distribution and relative proportion of TH- and NO-containing neurons in the CNS nerve ganglia were revealed in norm and under stress at 30°C for 10, 30, and 60 min. The initial stress stage (for 10 min) has been found to be accompanied by an increase of the relative content of TH-positive neurons in some CNS areas of both mollusc species. In intact Chlamys farreri nipponensis, the presence of NOS in the CNS and its significant activation under temperature stress might have possibly been an important neuroprotective component of stress reaction in some mollusc species.     

Spine-like astrocytic protrusions into large axon terminals

Summary Electron microscopic studies and three-dimensional graphic reconstructions from serial sections have shown that the large axon terminals of synaptic glomeruli in the ventrobasal nucleus of the rat are invaginated by spine-like protrusions from the astrocyte processes surrounding the glomeruli (micro-trophospongium). The astrocytic protrusions are similar in dimensions and internal morphology to the synapse-bearing dendritic excrescences that also invaginate the large axon terminals. Consequently astrocytic protrusions may be overlooked, or confused with dendritic excrescences sectioned at a non-synaptic level. The intimate neuronal—neuroglial relationship at such large axon terminals may reflect ion-exchange or metabolic interactions between the astrocytes and the axon terminal.We thank the British Council and Wellcome Trust for support, and Professors J. Z. Young and E. G. Gray for criticism and advice.     

Neuromodulatory effects of hydrogen peroxide on central neurons in the feeding network of the mollusc <Emphasis Type="Italic">Lymnaea stagnalis</Emphasis>

Hydrogen peroxide at a concentration of 100 μM was found to exert a pronounced modulatory effect on motor (R/L cells in B1–B4 clusters) and modulatory (R/L cerebral giant cells) neurons in the feeding neural network of the mollusc Lymnaea stagnalis as manifested in changes in the firing rate, membrane potential level and spike amplitude in these cells. The observed effects were reversible, transient, and reached their peak values in 1 min since application of the preparation. Injection of hydrogen peroxide into the cavity of the cephalopedal sinus resulted in no statistically significant changes in the parameters of mollusc feeding behavior. Hydrogen peroxide is assumed to act as a rapid neuromodulator towards neurons of the central feeding rhythm generator in Lymnaea stagnalis.     

Sertoli cells of adult rats “in vitro”

Summary A cell line obtained from isolated seminiferous tubules of adult rat testis has been studied in vitro over a period of 35 days.Light and electron microscopic studies performed from hour 2 to the end of culture have shown the presence of a monomorphic cell population. After 5–6 days of culture the cells formed a monolayer. The cytoplasm of the cells contained numerous lipid bodies and produced numerous projections. The nucleus showed several indentations and one or more nucleoli. From the 9th to the 15th day of culture the cells developed a large amount of endoplasmic reticulum, Golgi apparatus and aggregates of electron dense granules. From the 20th to 40th day the cell cultures progressively degenerated.Immunochemical analysis of the culture medium revealed the presence of estradiol-17, which reached its maximum production rate from the 8th day to the 18th day of culture. Corresponding to cell involution estradiol concentration underwent a rapid decrease.On the basis of morphological and biochemical data the cells could be considered Sertoli cells.This work was supported by Grants n. 74.00155.04 and n. 75.01224.04 from the Consiglio Nazionale delle Ricerche (C.N.R.), Rome, Italy, and by Istituto di Ricerca F. Angelini, Rome, ItalyPart of this work was presented at the 10th Italian Congress of Electron Microscopy. Ostuni 1–4 October 1975The excellent technical assistance of Miss Laura Vassallo, Daniela Venturini and Mr. Massimo Rosati and Mario Termine is deeply appreciated     

Integration of pecking,filter feeding and drinking mechanisms in waterfowl

This paper is one of several contributions in a series, illustrating the application of a specific deductive methodology to explain diversity of form. The methodology facilitates the explanation of feeding morphologies in various ducks as a transformation of the mallard's feeding design maximized for specific proportions of performance that are contributed by pecking and filter feeding mechanisms.The earlier described anatomy and formal analyses of the three mechanisms in the mallard served as the initial conditions used in simulation models. Four elements of the feeding system were chosen that play a major role in all three mechanisms. For each element, the main parameter was selected: storage capacity of the rostral mouth cavity, transport capacity of the rostral mouth tube, storage capacity of the caudal mouth cavity and transport capacity of the caudal mouth tube. The boundary conditions for the simulation were determined from internal organismic constraints. The total food uptake of the mallard was regarded as the function to be maximized. This object function is the summation of the food uptake by one second of pecking and one second of filter feeding. The drinking mechanism was shown not to interfere, since that mechanism operates sufficiently whenever the pumping mechanism works properly.The object function, made up by the pecking and filter feeding performances was graphed. From these graphs a morphospace was developed: the region within which modifications of the mouth design are feasible. This procedure allowed examination of the general hypothesis that different modifications of one design for a complex multi-role system are explainable from differences in proportions of the functional performance contributed by each of the roles.Two predictions were evaluated more specifically: 1) If filter feeding performance must increase for a specific change in total food uptake, the volume of the rostral mouth cavity must increase; this requires widening and lengthening of the rostral maxillar portion and also a phase shift in jaw and lingual motion patterns, increasing the stroke volume. 2) If pecking performance must increase, the transport capacity of the rostral mouth tube must increase; this requires shortening of the maxillar mid portion. These two predictions regarding change in mouth morphology were borne out by shovelers and tufted ducks, respectively.The deductive analysis of the feeding system's morphospace allowed the explanation of the wide diversity of forms in the duck mouth designs as emerging from the great radiation capacity of the ancestral duck's mouth design: it is a versatile, potentially multi-role system in which pecking, drinking and filter feeding mechanisms are mutually very tolerant and, by epiphenomena, includes the elements of a grazing mechanism. In addition, the deduced morphospace was shown to explain phenotypic plasticity, since it explains the occurrence of two morphotypes that develop due to habitat discrimination: one type that has been forced to filter feed, and one type that feeds by pecking.Address reprint requests to Dr. G.A. Zweers     

Alien molluscs affect the composition and diversity of native macroinvertebrates in a sandy flat of Lake Neuchâtel,Switzerland

The spread of alien molluscs is a serious threat to native biodiversity in fresh waters. Alien freshwater molluscs may deplete the resources of native species and alter the physical structure of the habitat through their shell mass. These changes might have both positive and negative effects on native community members. We investigated the native macroinvertebrate community in relation to the densities of four alien mollusc species (Corbicula fluminea, Dreissena polymorpha, Potamopyrgus antipodarum and Lithoglyphus naticoides) in a sandy flat of Lake Neuchatel, Switzerland. The habitat examined was dominated by these alien mollusc species. The abundance of the alien molluscs did not directly impact the native community assembly. However, C. fluminea and D. polymorpha influenced the composition and diversity of native macroinvertebrates by transforming the sandy substratum into a partly hard substratum habitat. Substantial differences in community composition between shallow (<3.5 m) and (≥5 m) deep sites were recorded. At shallow sites, the abundance of D. polymorpha was significantly reduced as a result of depth-selective feeding of ducks. A controlled shell decay study revealed that shells of alien molluscs (C. fluminea, D. polymorpha) persist for a longer period in the sediment than those of native molluscs. Consequently, shells of alien molluscs have a long-lasting impact by modifying the sandy habitat. This form of ecosystem engineering favours the occurrence of several native taxa, but is disadvantageous for other taxa with specific habitat requirements, and thus can be regarded as an indirect impact of competition.     

Trace Elements in Edible Rocky Shore Species: Effect of Sewage Discharges and Human Health Risk Implications

Sewage pollution is a worldwide concern and can result in increasing levels of trace elements in the environment that can pose serious risks both to wildlife and human health. This highlights the importance of studying the role of sewage discharges in the contamination of aquatic systems, especially in rocky shores, since part of our food resources is directly collected from coastal waters. For this purpose, the accumulation of trace elements (Cu, Zn, Pb, Ni, Co, Cd, Fe, Mn, and As) by edible molluscs (Mytilus galloprovincialis, Patella ulyssiponensis, and Phorcus lineatus) was compared between one sewage-impacted area and two reference areas.

This study suggests that the concentrations of trace elements in the soft tissues of the selected molluscs can be affected by the presence of sewage discharges, and that limpets seem to be the best bioindicator. Moreover, the sewage pollution increased the concentrations of As in the mollusc species, emphasizing its potential damaging effects on natural systems and on edible species.     

Echinoid bioerosion from the Pliocene of NE Spain

In the present study a series of rasping traces onshells and limestone pebbles from the Pliocene of l'Empordà (Catalunya, NE Spain) are described. The traces have been attributed to the ichnospecies Gnathichnus pentaxBromley, 1975. This type of rasping traces is produced today by regular echinoids. Comparison with the traces produced by P. lividus (Lmk) of the Catalan coast confirms its origin.     

Nitrogen fixation by intact colonies of the termite Nasutitermes corniger

Summary Biosteres longicaudatus Ashmead (Hymenoptera: Bracon dae) is a solitary endoparasite of Anastrepha suspensa larvae (Diptera: Tephritidae), which live in fruit tissue. Larvae make andible noises within macerated fruit or larval medium in which they are reared. Parasite females readily located normal, mobile larvae and spent a mean of 16.5±4.7 min/visit to parasitize these hosts. In contrast, females were unable to locate etherized or dead hosts and abandoned them after only 1.9±0.9 and 2.3±0.8 min, respectively. Females of all ages, with and without oviposition experience, exhibited non-random search and ovipositor probe behaviors in response to artifically created vibration. This response was influenced primarily by the number of mature eggs in the ovaries. These findings suggest that 1) an accumulation of mature eggs in the ovaries increase the appetitive drive of females to find and oviposit in hosts and 2) host sound/vibration produced either by movement of hosts through the medium and/or by the rasping mouth hooks during feeding. is used by parasites as a releaser for host finding behavior as well as a cue to the location of the host within the substrate.     

Parasitism of Molluscs by Nematodes: Types of Associations and Evolutionary Trends

Although there are no confirmed fossil records of mollusc parasitic nematodes, diverse associations of more than 108 described nematode species with slugs and snails provide a fertile ground for speculation of how mollusc parasitism evolved in nematodes. Current phylogenic resolution suggests that molluscs have been independently acquired as hosts on a number of occasions. However, molluscs are significant as hosts for only two major groups of nematodes: as intermediate hosts for metastrongyloids and as definitive hosts for a number of rhabditids. Of the 61 species of nematodes known to use molluscs as intermediate hosts, 49 belong to Metastrongyloidea (Order Strongylida); of the 47 species of nematodes that use molluscs as definitive hosts, 33 belong to the Order Rhabditida. Recent phylogenetic hypotheses have been unable to resolve whether metastrongyloids are sister taxa to those rhabditids that use molluscs as definitive hosts. Although most rhabditid nematodes have been reported not to kill their mollusc hosts prior to their reproduction, some species are pathogenic. In fact, infective juveniles of Phasmarhabditis hermaphrodita vector a lethal bacterium into the slug host in which they reproduce. This life cycle is remarkably similar to the entomopathogenic nematodes in the families Steinernematidae and Heterorhabditidae. Also, the discoveries of Alloionema and Pellioditis in slugs are interesting, as these species have been speculated to represent the ancestral forms of the entomopathogenic nematodes. Development of the infective stage appears to be an important step toward the acquisition of molluscs as definitive hosts, and the association with specific bacteria may have arisen in conjunction with the evolution of necromeny.     

Abstractions can be causes — A response to professor hogan

In Can Abstractions be Causes, David Johnson defends the view that abstractions can have causal force. He offers as his own example of natural kinds ecological niches, arguing that the causal force of these niches in nature is akin to the force of Aristotelian final causes. He concludes that, rooted as it is in seventeenth century mechanism, the currently-accepted model of causality which recognises only efficient causes is inadequate to the needs of contemporary science. In Natural Kinds and Ecological Niches — Response to Johnson's Paper, Melinda Hogan offers a critique of Johnson's paper which, by begging the question in favor of the very sort of causality Johnson seeks to supplement, misses the epistemological implications of his idea. In this paper I will attempt to clarify and defend Johnson's position, pointing out some of its implications for the epistemology of science in general.