Quantitative modelling of the impact of molluscan invasions
Quantitative models based on two statistical techniques (logistic regression and categorical tree analysis) were applied in order to predict the chance that 15 mollusc species, not yet in natural ecosystems of U.S., would cause damage if they became established. No significant relationship was evident at the U.S. scale (i.e. 48 contiguous states) but recently established molluscs within the Laurentian Great Lakes were more likely to cause negative impacts. This may reflect changing environmental conditions, changing patterns of trade, or may be an indication of "invasional meltdown." The analyses could be extended to other taxa and ecosystems and offer a number of improvements over qualitative risk assessments currently used.
Keller, R.P., J.M. Drake and D.M. Lodge, 2007. Fecundity as a basis for risk assessment of nonindigenous freshwater molluscs Conservation Biology 21(1) 191-200.
defence of mussels to different bacteria
Adult mussels were challenged with different strains of bacteria to determine the specificity of three antimicrobial peptides (AMPs) involved in their immunity - defensin, mytilin and myticin. Control mussels were exposed to heat shock. Gene expression for Heat Shock Protein 70 represented a non-specific response to stress. AMP genes regulated differed with the challenging bacteria, confirming that at least some of the innate immune mechanisms are specifically orientated.
Cellura, C., M. Toubiana, N. Parrinello and P. Roch, 2007. Specific expression of antimicrobial peptide and HSP70 genes in response to heat-shock and several bacterial challenges in mussels. Fish & Shellfish Immunology 22(4) 340-350.
Neural Network based on cephalopod statocyst
Cephalopod statocysts contain a biological neural network analogous to the vertebrate vestibular system that provides the animal with sensory information on its orientation and movements in space. The statocyst neurons are fully accessible to physiological investigation and the system provides an excellent model for describing the mechanisms underlying the operation of a sophisticated neural network.
Williamson, R. and A. Chrachri, 2007. A model biological neural network: the cephalopod vestibular system. Philosophical Transactions of the Royal Society B – Biological Sciences 362 (1479) 473-481.
evidence of predation
A model derived from observational studies on bird feeding behavior might find application in the study of avian predation of mollusks from historical, ecological, and paleoecological perspectives. The model was tested on 3 distinct habitats: lagoon, bay, and gravel bar. Comparison of species’ diversity and abundance in sympatric life and death assemblages (i.e. fidelity analysis), revealed significant differences in all assemblages. However, the gravel bar death assemblage was found to be more similar in composition to the life assemblages than to the other two death assemblages, suggesting that the gravel bar approximates the present day composition of the local mollusc fauna ecosystem more closely than either the bay or lagoon death assemblages. The bar deposit, with its highly fragmented but pristine shells, dominant fracture patterns, and monospecific composition, suggests that supratidal deposits resulting from bird predation can be identified using indirect methods based on damage patterns in shell assemblages.
Stempien, J.A. 2007. Detecting avian predation on bivalve assemblages using indirect methods. Journal of Shellfish Research 26(1): 271-280.
Sticking together: a way to facilitate survival and reproduction?
Juvenile fluted giant clams (Tridacna squamosa), move and aggregate over time. The hypothesis that clams are attracted to conspecifics was tested by recording clam movement with respect to five types of fixed 'targets' (i.e. live clam, fouled clam shell, foul-free clam shell, random inanimate object and none), and a choice experiment using bidirectional water inflow with clam effluent as one source. Results indicated the presence of chemical signaling among clams, leading to movement toward one another and clumping. Aggregation could serve several ecological functions, such as defence against predation, physical stabilization and facilitation of reproduction. However, declining densities reduce the opportunity for conspecific clumping, and local stocks could face increased predation.
Huang, D.W., P.A. Todd and J.R. Guest. 2007 Movement and aggregation in the fluted giant clam (Tridacna squamosa L.). Journal of Experimental Marine Biology and Ecology 342(2): 269-281.
Mixing colours gives pearls their look
The nature of pigments in naturally colored pearls is a little clearer thanks to a study of Raman scattering in 30 coloured cultured freshwater pearls of Hyriopsis cumingi. The originality of this work is that seven different excitation wavelengths (1064 nm, 676.44 nm, 647.14 nm, 514.53 nm, 487.98 nm, 457.94 nm, 363.80 nm) were used. The results showed certain peaks that are not detected in white pearls, indicating that they are directly related to the body color. Up to nine different pigments may be detected in the same pearl. Their general chemical formula is R-(CH=CH)N-R' with N = 6-14. All colored samples contained at least four pigments (N = 8-11). The chemical nature of the chain ends is still unknown, but it is possible that these polyenes are complexed with carbonate molecules of the nacre. The authors suggest that different colors are due to different mixtures, not to a simple change of pigment, and compare this mechanism to similar coloration mechanisms found in for example parrots feathers and in some corals.
Karampelas, S., E. Fritsch, J.Y. Mevellec, J.P. Gauthier, S. Sklavounos and T. Soldatos, 2007. Determination by Raman scattering of the nature of pigments in cultured freshwater pearls from the mollusk Hyriopsis cumingi. Journal of Raman Spectroscopy 38(2) 217-230.
History of management of oysters in East Australia
Why did current management options in the oyster industry on the east coast of Australia arise? Following thousands of years of harvest, legislation brought about by unsustainable exploitation led the oyster industry to aquaculture in 1884. Translocation of oyster stock for fattening, from New Zealand to Australian east coast estuaries, was encouraged. However, this activity resulted in "mudworm disease" appearing on the east coast between 1880 and 1900. The pandemic permanently destroyed natural sub-tidal oyster reefs and forced the oyster industry to adopt avoidance farming techniques including intertidal farming.
Ogburn, D.M., I. White and D.P. McPhee, 2007. The disappearance of oyster reefs from eastern Australian estuaries - Impact of colonial settlement or mudworm invasion? Coastal Management 35(2-3) 271-287.
Winkle saliva turns on seaweed’s defences
Plant resistance was induced in the marine macroalga Ascophyllum nodosum in the absence of herbivory by application of a-amylase, known to exist in mollusc saliva. Resistance was developed by an increase in phlorotannins (compounds associated with defence against herbivory), and these subsequently produced changes in the behaviour of Littorina obtusata, i.e. reduced consumption, more but smaller meals and greater movement. Such changes in herbivore behaviour and plant chemistry provide evidence that brown algae, like higher plants, use saliva-based signals in the induction of defence against herbivory.
Coleman, R.A., S. J. Ramchunder, A.J. Moody and A. Foggo, 2007. An enzyme in snail saliva induces herbivore-resistance in a marine alga. Functional Ecology 21(1) 101-106.
Modelling gene flow in endangered populations
The first fine scale analysis of gene flow under different scenarios of habitat connectivity for the endangered mound spring snail, Fonscochlea accepta applied different mathematical approaches, e.g. F-Statistics, Mantel correlation analyses, and Bayesian assignment tests. These produced varying results; perhaps because they use different information. Taken together, however, they provide data on contemporary and historical estimates of gene flow and the influence of landscape dynamics on the spatial genetic patterning of the springs.
Wilmer, J.W. and C. Wilcox, 2007. Fine scale patterns of migration and gene flow in the endangered mound spring snail, Fonscochlea accepta (Mollusca : Hydrobiidae) in arid Australia. Conservation Genetics 8(3): 617-628.
Very slow development of Antarctic bivalves
Embryos of the large infaunal clam Laternula elliptica and the scallop Adamussium colbecki, from Antarctica, develop extremely slowly. All of the limited data for Antarctic species are well above the Arrhenius plot for the overall bivalve data, with a Q10 of 11.8, well outside the expected range for biological systems. Either the kinetics of biological systems do not apply to Antarctic bivalve molluscs, or some other factor that cannot be compensated for becomes important at low temperature.
Peck, L.S., D.K. Powerll and P.A. Tyler, 2007. Very slow development in two Antarctic bivalve molluscs, the infaunal clam Laternula elliptica and the scallop Adamussium colbecki. Marine Biology 150(6) 1191-1197.
New test species for assessing endocrine disruptors
Prosobranch snails are promising candidates for the assessment of endocrine-active chemicals (e.g. xeno-androgens and xeno-estrogens). The freshwater mudsnail Potamopyrgus antipodarum, the freshwater ramshorn snail Marisa cornuarietis, and the marine netted whelk Nassarius reticulatus are highly sensitive toward xeno-androgens, where exposure may result in development of imposex and reduction of fertility or embryo production, and xeno-estrogens, where. exposure may result in stimulation of egg production and embryo production, and increased weight of glands. A comparison of the three test species with regard to sensitivity and practical aspects in routine application favours the freshwater mudsnail P. antipodarum for a standardized procedure, and this reproduction test will be introduced into the OECD guideline program for standardization in the near future.
Duft, M., C. Schmitt, J. Bachmann, C. Brandelik, U. Schulte-Oehlmann and J. Oehlmann, 2007. Prosobranch snails as test organisms for the assessment of endocrine active chemicals - an overview and a guideline proposal for a reproduction test with the freshwater mudsnail Potamopyrgus antipodarum. Ecotoxicology 16(1), 169-182.
Assessing the possibility to employ basommatophora as test species for endocrine disruptors
A review summarizing the neuroendocrine control of reproduction in aquatic basommatophorans, with a comprehensive description of selected in vivo laboratory and semi-field studies which provide evidence for possible endocrine disrupting effects of estrogenic and androgenic test compounds.
Lagadic, L., M.A. Coutellec and T. Caquet, 2007. Endocrine disruption in aquatic pulmonate molluscs: few evidences, many challenges. Ecotoxicology 16(1) 45-59.
A survey of parasites of freshwater snails
A survey of digenean cercariae and metacercariae from the pond snail Lymnaea stagnalis in Austria, Czech Republic, South-East Germany, Poland and Slovak Republic, based on a study of 3,628 snails. A simple key to identification of cercariae and metacercariae, together with illustrations, is provided.
Faltynkova, A., V. Nasincova and L. Kablaskova, 2007. Larval trematodes (Digenea) of the great pond snail, Lymnaea stagnalis (L.), (Gastropoda, Pulmonata) in Central Europe: A survey of species and key to their identification. Parasite – Journal de la Societe Francaise de Parasitologie 14(1) 39-51.
Molluscan mantle: complex and modular
Over 25% of the genes expressed in the mantle of the vetigastropod Haliotis asinina form the secretome, encoding secreted proteins. This indicates that hundreds of proteins probably contribute to shell fabrication and patterning. Almost 85% of the secretome encode novel proteins; remarkably, only 19% of these have identifiable homologues in the full genome of the patellogastropod Lottia scutum. Patterned expression of a subset of genes along the length of the mantle indicates roles in shell ornamentation. For example, Has-sometsuke maps precisely to pigmentation patterns in the shell - the first case of a gene product to be involved in molluskan shell pigmentation. The composition of this novel mantle-specific secretome suggests that there are significant molecular differences in the ways in which gastropods synthesize their shells.
Jackson, D.J., C. McDougall, K. Green, F. Simpson, G. Worheide and B.M. Degnan, 2006. A rapidly evolving secretome builds and patterns a sea shell. BMC Biology 4 Art 40.
Body size and objects in visual background: Cuttlefish go for matching outfits
Cuttlefish (Sepia officinalis) are able to match their disruptive body patterning with increasing size of background objects as they grow from hatchling to adult size. Black and white chequer boards, with cheque sizes corresponding to 4, 12, 40, 120, 400 and 1200% of the area of the cuttlefish's white square (a neurophysiologically controlled component of the skin), were created separately for seven size classes. Disruptive body patterns were evoked whenever the check size measured either 40 or 120% of the area of the cuttlefish's white square regardless of the animals’ size.
Barbosa, A., L.M. Mather, C. Chubb, C. Florio, C.C. Chiao and R.T. Hanlon, 2007. Disruptive coloration in cuttlefish: a visual perception mechanism that regulates ontogenetic adjustment of skin patterning. Journal of Experimental Biology 210 (7): 1139-1147.
Temperature stress exacerbates toxicity of Cd in the eastern oyster Crassostrea virginica leading to elevated oxidative stress in mitochondria. This may have important implications for survival of poikilotherms in polluted environments during seasonal warming and/or global climate change. The study also suggests a novel temperature-dependent mechanism of allosteric regulation of TCA flux in oyster mitochondria.
Cherkasov, A.A., R.A. Overton, E.P. Sokolov and I.M. Sokolova, 2007. Temperature-dependent effects of cadmium and purine nucleotides on mitochondrial aconitase from a marine ectotherm, Crassostrea virginica: a role of temperature in oxidative stress and allosteric enzyme regulation Journal of Experimental Biology 210 (1): 46-55.
predation attacks on mussels
Three types of diagnostic damage are inflicted by crab predation: nibbles, nibbles and chips, and peels; tumbling shells yielded different diagnostic breakage patterns: crescentic chips, angular chips, and slivered chips, whereas crushed shells and shells with fractured margins were caused by predation and trampling. Overall, the source of damage can be correctly identified in 74% of shells. Correctly identifying crab predation may aid studies of trophic interactions.
Cintra-Buenrostro, C.E. 2007. Trampling, peeling and nibbling mussels: An experimental assessment of mechanical and predatory damage to shells of Mytilus trossulus (mollusca : mytilidae). Journal of Shellfish Research 26(1) 221-231.
Sequencing the cDNA of the hemocyanin from the protobranch bivalve, Nucula nucleus, reveals a closer relationship to gastropod hemocyanin than to cephalopod hemocyanin. Assuming a molecular clock, the last common ancestor of protobranch and gastropods lived 494 million +/- 50 million years ago, in conformity with fossil records from the late Cambrian.
Bergmann, S., J. Markl and B. Lieb, 2007. The first complete cDNA sequence of the hemocyanin from a bivalve, the protobranch Nucula nucleus. Journal of Molecular Evolution 64(5) 500-510.
the guilty part
Herpes-like viral infections occur in different bivalve mollusc species throughout the world, and are associated with high mortalities among hatchery-reared larvae and juveniles of different bivalve species. The herpes-like viruses in bivalve molluscs has been traditionally diagnosed by light and transmission electron microscopy. The genome sequencing of oyster herpesvirus 1, allowed the development of DNA-based diagnostic techniques. The study reviews the literature on DNA extraction methods, primers, PCR strategies, and confirmatory procedures used for the detection and identification of herpesviruses that infect bivalve mollusks.
Batista, F.M., I. Arzul, J.F. Pepin, F. Ruano, C.S. Friedman, P. Boudry and T. Renault, 2007. Detection of ostreid herpesvirus 1 DNA by PCR in bivalve molluscs: a critical review. Journal of Virological Methods, 139(1) 1-11.