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.
Specific
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.
Artificial
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.
Indirect
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.
Too much
stress?
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.
Identifying
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.
Tracing
ancestors
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.
Identifying
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.