The shell division of the nucleus accumbens receives noradrenergic input from neurons in the nucleus of the solitary tract (NTS) that transmit information regarding fluctuations in peripheral hormonal and autonomic activity. Accumbens shell neurons also receive converging inputs from limbic areas such as the hippocampus and amygdala that process newly acquired information. However, few studies have explored whether peripheral information regarding changes in emotional arousal contributes to memory processing in the accumbens. The beneficial effects on memory produced by emotional arousal and the corresponding activation of NTS neurons may be mediated through influences on neuronal activity in the accumbens shell during memory encoding. To explore this putative relationship, Experiment 1 examined interactions between the NTS and the accumbens shell in modulating memory for responses acquired after footshock training in a water-motivated inhibitory avoidance task. Memory for the noxious shock was significantly improved by posttraining excitation of noradrenergic NTS neurons. The enhanced retention produced by activating NTS neurons was attenuated by suppressing neuronal activity in the accumbens shell with bupivacaine (0.25%/0.5μl). Experiment 2 examined the direct involvement of accumbens shell noradrenergic activation in the modulation of memory for psychologically arousing events such as a reduction in perceived reward value. Noradrenergic activation of the accumbens shell with phenylephrine (1.0μg/0.5μl) produced an enhancement in memory for the frustrating experience relative to control injections as evidenced by runway performance on an extended seven-day retention test. These findings demonstrate a functional relationship between NTS neurons and the accumbens shell in modulating memory following physiological arousal and identifies a role of norepinephrine in modulating synaptic activity in the accumbens shell to facilitate this process.
Purified human pararotavirus obtained from stool samples from a 6-month-old infant was characterized. Electron microscopy of the viral particles subjected to different treatments suggested that the protein shells differed from those described for rotavirus. Treatment with both EDTA or ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid in the presence or absence of Mg2+ seemed to convert the virions into core particles by removal of both the outer and inner shells, and no particles equivalent to single-shelled rotavirus were observed. Different procedures were used to activate the human pararotavirus-associated RNA-dependent RNA polymerase. The enzyme was not activated by chelating agents or by thermal shock as in rotavirus. Activation by thermal shock occurred only in the presence of the four ribonucleoside triphosphates and Mg2+. However, the polymerase of pararotavirus was found to be similar to those described for rotaviruses. When in vitro transcripts were analyzed, 11 RNA species having a migration pattern similar to that of the original genomic RNA were detected.
Evidence suggests that inertial cavitation plays an important role in the renal injury incurred during shock-wave lithotripsy. However, it is unclear how tissue damage is initiated, and significant injury typically occurs only after a sufficient dose of shock waves. While it has been suggested that shock-induced shearing might initiate injury, estimates indicate that individual shocks do not produce sufficient shear to do so. In this paper, we hypothesize that the cumulative shear of the many shocks is damaging. This mechanism depends upon whether there is sufficient time between shocks for tissue to relax to its unstrained state. We investigate the mechanism with a physics-based simulation model wherein the the basement membranes that define the tubules and vessels in the inner medulla are represented as elastic shells surrounded by viscous fluid. Material properties are estimated from in vitro tests of renal basement membranes and documented mechanical properties of cells and extracellular gels. Estimates for the net shear deformation from a typical lithotripter shock (~ 0.1%) are found from a separate dynamic shock simulation. The results suggest that the larger interstitial volume (~ 40%) near the papilla tip gives the tissue there a relaxation time comparable to clinical shock delivery rates (~ 1Hz), thus allowing shear to accumulate. Away from the papilla tip, where the interstitial volume is smaller (≲ 20%), the model tissue relaxes completely before the next shock would be delivered. Implications of the model are that slower delivery rates and broader focal zones should both decrease injury, consistent with some recent observations.
Shock-wave lithotripsy; renal injury; tissue damage; numerical simulation
The Mediterranean land snail Xeropicta derbentina forms huge populations in Southern France. In order to characterize heat exposure and the induction of the 70-kD heat shock protein (Hsp70) response system during the life cycle of this snail, a selected population from the Vaucluse area, Provence, was investigated encompassing the issues of morphological life cycle parameters (shell size and colouration), the daily courses of heat exposure at different heights above the ground, of shell temperature, and that of the individual Hsp70 levels. The study covered all four seasons of the year 2011. Snails were found to be annual, reaching their final size in August. The shell colouration pattern showed high variation in juveniles (spring) with a strong tendency towards becoming uniformly white at old age in autumn. In all seasons, ambient air temperature decreased with increasing distance from the ground surface during daytime while remaining constantly low in the night. Overall, the Hsp70 level of individuals followed the ambient temperature during diurnal and seasonal variations. Correlation analysis revealed a positive association of individual shell temperature and Hsp70 level for the most part of the life cycle of the snails until late summer, whereas a negative correlation was found for aged animals indicating senescence effects on the capacity of the stress response system.
Heat shock response; Mediterranean land snail; Stress proteins; Temperature; Life cycle
The enzymatic transfer of phosphoryl groups is central to the control of many cellular processes. One of the phosphoryl transfer mechanisms, that of acetate kinase, is not completely understood. Besides better understanding of the mechanism of acetate kinase, knowledge of the structure of butyrate kinase 2 (Buk2) will aid in the interpretation of active-site structure and provide information on the structural basis of substrate specificity. The gene buk2 from Thermotoga maritima encodes a member of the ASKHA (acetate and sugar kinases/heat shock cognate/actin) superfamily of phosphotransferases. The encoded protein Buk2 catalyzes the phosphorylation of butyrate and isobutyrate. We have determined the 2.5-Å crystal structure of Buk2 complexed with (β,γ-methylene) adenosine 5′-triphosphate. Buk2 folds like an open-shelled clam, with each of the two domains representing one of the two shells. In the open active-site cleft between the N- and C-terminal domains, the active-site residues consist of two histidines, two arginines, and a cluster of hydrophobic residues. The ATP binding region of Buk2 in the C-terminal domain consists of abundant glycines for nucleotide binding, and the ATP binding motif is similar to those of other members of the ASKHA superfamily. The enzyme exists as an octamer, in which four disulfide bonds form between intermolecular cysteines. Sequence alignment and structure superposition identify the simplicity of the monomeric Buk2 structure, a probable substrate binding site, the key residues in catalyzing phosphoryl transfer, and the substrate specificity differences among Buk2, acetate, and propionate kinases. The possible enzyme mechanisms are discussed.
Almost every major war in the last century involving western nations has seen combatants diagnosed with a form of post-combat disorder. Some took a psychological form (exhaustion, combat fatigue, combat stress reaction and post-traumatic stress disorder), while others were characterized by medically unexplained symptoms (soldier's heart, effort syndrome, shell shock, non-ulcer dyspepsia, effects of Agent Orange and Gulf War Syndrome). Although many of these disorders have common symptoms, the explanations attached to them showed considerable diversity often reflected in the labels themselves. These causal hypotheses ranged from the effects of climate, compressive forces released by shell explosions, side effects of vaccinations, changes in diet, toxic effects of organophosphates, oil-well fires or depleted-uranium munitions. Military history suggests that these disorders, which coexisted in the civilian population, reflected popular health fears and emerged in the gaps left by the advance of medical science. While the current Iraq conflict has yet to produce a syndrome typified by medically unexplained symptoms, it is unlikely that we have seen the last of post-combat disorders as past experience suggests that they have the capacity to catch both military planners and doctors by surprise.
post-combat disorders; shell shock; post-traumatic stress disorder; disordered action of the heart; Gulf War Syndrome
Nitric oxide synthase (NOS) enzymes synthesize nitric oxide, a signal for vasodilatation and neurotransmission at low levels, and a defensive cytotoxin at higher levels. The high active-site conservation among all three NOS isozymes hinders the design of selective NOS inhibitors to treat inflammation, arthritis, stroke, septic shock, and cancer. Our structural and mutagenesis results identified an isozyme-specific induced-fit binding mode linking a cascade of conformational changes to a novel specificity pocket. Plasticity of an isozyme-specific triad of distant second- and third-shell residues modulates conformational changes of invariant first-shell residues to determine inhibitor selectivity. To design potent and selective NOS inhibitors, we developed the anchored plasticity approach: anchor an inhibitor core in a conserved binding pocket, then extend rigid bulky substituents towards remote specificity pockets, accessible upon conformational changes of flexible residues. This approach exemplifies general principles for the design of selective enzyme inhibitors that overcome strong active-site conservation.
nitric oxide synthase; isozyme-specific inhibitor; induced-fit; x-ray crystallography; quinazoline; aminopyridine; drug design
Mollusk shell is one kind of potential biomaterial, but its vague mineralization mechanism hinders its further application. Mollusk shell matrix proteins are important functional components that are embedded in the shell, which play important roles in shell formation. The proteome of the oyster shell had been determined based on the oyster genome sequence by our group and gives the chance for further deep study in this area. The classical model of shell formation posits that the shell proteins are mantle-secreted. But, in this study, we further analyzed the shell proteome data in combination with organ transcriptome data and we found that the shell proteins may be produced by multiple organs though the mantle is still the most important organ for shell formation. To identify the transport pathways of these shell proteins not in classical model of shell formation, we conducted a shell damage experiment and we determined the shell-related gene set to identify the possible transport pathways from multiple organs to the shell formation front. We also found that there may exist a remodeling mechanism in the process of shell formation. Based on these results along with some published results, we proposed a new immature model, which will help us think about the mechanism of shell formation in a different way.
Cytomegalovirus reactivation occurred in one third of patients and was associated with prolonged ventilation and stay in an intensive care unit.
Cytomegalovirus (CMV) is a pathogen of emerging importance for patients with septic shock. In this prospective study, 25 immunocompetent CMV-seropositive patients with septic shock and an intensive care unit stay of >7 days were monitored by using quantitative pp65-antigenemia assay, shell vial culture, and virus isolation. Within 2 weeks, active CMV infection with low-level pp65-antigenemia (median 3 positive/5 × 105 leukocytes) developed in 8 (32%) patients. Infection was controlled within a few weeks (median 26 days) without use of antiviral therapy. Duration of intensive care and mechanical ventilation were significantly prolonged in patients with active CMV infection. CMV reactivation was associated with concomitant herpes simplex virus reactivation (p = 0.004). The association between active CMV infection and increased illness could open new therapeutic options for patients with septic shock. Future interventional studies are required.
sepsis; reactivation; cytomegalovirus; herpes simplex virus; diagnostic assays
The heat shock cognate protein 70 (Hsc70) is a member of a 70-kDa heat shock protein (HSP70) family that functions as molecular chaperones. In this study, a novel Hsc70 gene from Chinese soft-shelled turtle (Pelodiscus sinensis) (tHsc70) was identified. The tHsc70 full-length complementary DNA (cDNA) is 2 272 bp long with a 1 941-bp open reading frame (ORF) encoding 646 amino acids. Three characteristic signature regions of the HSP70 family, two major domains of an adenosine triphosphate (ATP)/guanosine triphosphate (GTP) binding domain (ABD), and a substrate-binding domain (SBD) were present in the predicted tHsc70 amino acid sequence. The tHsc70 gene was expressed in Escherichia coli BL21 and the expression product reacted with the anti-Hsc70 mouse monoclonal antibody by Western blotting. Homology analysis revealed that tHsc70 shared identity from 53.9% to 87.7% at the nucleotide level, and 49.1% to 99.5% at the amino acid level with the known Hsc70s. Phylogenetic analysis showed that tHsc70 was clustered together with the Hsc70 gene of another reptile species (Alligator mississippiensis). The tHsc70 was expressed in the liver, lung, heart, and skeletal muscle. The expression patterns of tHsc70 messenger RNA (mRNA) differed among different tissues under different durations of heat stress at 40 °C. Adaptation at 25 °C for 1 h after heat stress was also different among tissues and length of heat stress. Irrespective of different profiles of expression under heat stress, tHsc70 may play roles in protecting turtles from thermal stress.
Pelodiscus sinensis; Heat shock cognate protein 70 (Hsc70); Phylogenetic analysis; Heat stress
How does the sequence of a single Small Heat Shock Protein (sHSP) assemble into oligomers of different sizes? To gain insight into the underlying structural mechanism, we determined the crystal structure of an engineered variant of Methanocaldococcus jannaschii Hsp16.5 wherein a 14 amino acid peptide from human heat shock protein 27 (Hsp27) was inserted at the junction of the N-terminal region and the α-crystallin domain. In response to this insertion, the oligomer shell expands from 24 to 48 subunits while maintaining octahedral symmetry. Oligomer rearrangement does not alter the fold of the conserved α-crystallin domain nor does it disturb the interface holding the dimeric building block together. Rather, the flexible C-terminal tail of Hsp16.5 changes its orientation relative to the α-crystallin domain which enables alternative packing of dimers. This change in orientation preserves a peptide-in-groove interaction of the C-terminal tail with an adjacent β-sandwich thereby holding the assembly together. The interior of the expanded oligomer, where substrates presumably bind, retains its predominantly non-polar character relative to the outside surface. New large windows in the outer shell provide increased access to these substrate-binding regions, thus accounting for the higher affinity of this variant to substrates. Oligomer polydispersity regulates sHSPs chaperone activity in vitro and has been implicated in their physiological roles. The structural mechanism of Hsp16.5 oligomer flexibility revealed here, which is likely to be highly conserved across the sHSP superfamily, explains the relationship between oligomer expansion observed in disease-linked mutants and changes in chaperone activity.
Small heat shock proteins; Hsp16.5; Chaperone; crystal structure
The core shell of hepatitis B virus is a potent immune stimulator, giving a strong neutralizing immune response to foreign epitopes inserted at the immunodominant region, located at the tips of spikes on the exterior of the shell. Here, we analyze structures of core shells with a model epitope inserted at two alternative positions in the immunodominant region. Recombinantly expressed core protein assembles into T = 3 and T = 4 icosahedral shells, and atomic coordinates are available for the T = 4 shell. Since the modified protein assembles predominantly into T = 3 shells, a quasi-atomic model of the native T = 3 shell was made. The spikes in this T = 3 structure resemble those in T = 4 shells crystallized from expressed protein. However, the spikes in the modified shells exhibit an altered conformation, similar to the DNA containing shells in virions. Both constructs allow full access of antibodies to the foreign epitope, DPAFR from the preS1 region of hepatitis B virus surface antigen. However, one induces a 10-fold weaker immune response when injected into mice. In this construct, the epitope is less constrained by the flanking linker regions and is positioned so that the symmetry of the shell causes pairs of epitopes to come close enough to interfere with one another. In the other construct, the epitope mimics the native epitope conformation and position. The interaction of native core shells with an antibody specific to the immunodominant epitope is compared to the constructs with an antibody against the foreign epitope. Our findings have implications for the design of vaccines based on virus-like particles.
► The HBV core shell is highly immunogenic and is being used as a vaccine carrier. ► Insertion of model epitopes into the immunodominant region changes the structure. ► Alternative positions of an epitope give different structures and immunogenicity. ► The structural differences lead to different labeling with antibody fragments. ► We conclude that three‐dimensional structural analysis will be important in vaccine design.
EM, electron microscopy; Fab, fragment of antibody; Fv, fragment of antibody variable region; HBV, hepatitis B virus; L1, linker 1; L2, linker 2; MIR, major immunodominant region; PBS, phosphate-buffered saline; 3D, three‐dimensional; cryomicroscopy; image processing; vaccine carriers; virus-like particles; improved immunogenicity
Psychotrauma occurs as a result to a traumatic event, which may involve witnessing someone's actual death or personally experiencing serious physical injury, assault, rape and sexual abuse, being held as a hostage, or a threat to physical or psychological integrity. Post-traumatic stress disorder (PTSD) is an anxiety disorder and was defined in the past as railway spine, traumatic war neurosis, stress syndrome, shell shock, battle fatigue, combat fatigue, or post-traumatic stress syndrome (PTSS). If untreated, post-traumatic stress disorder can impair relationships of those affected and strain their families and society. Deployed soldiers are especially at a high risk to be affected by PTSD but often receive inadequate treatment. Reviews to date have focused only on a single type of treatment or groups of soldiers from only one country. The aim of the current review was to evaluate characteristics of therapeutic methods used internationally to treat male soldiers' PTSD after peacekeeping operations in South Eastern Europe and the Gulf wars.
This systematic literature review returned results pertaining to the symptoms, diagnosis, timing and effectiveness of treatment. Sample groups and controls were relatively small and, therefore, the results lack generalizability. Further research is needed to understand the influence and unique psychological requirements of each specific military operation on the internationally deployed soldiers.
Post-traumatic stress disorder (PTSD) is one of the anxiety disorders recently included in the Diagnostic and Statistical Manual of Mental Disorders, Third Edition (DSM-III).1 The disorder refers to the psychological sequelae that may follow a significant stressor. The military has previously referred to PTSD as “war neurosis,” “shell shock,” and “combat neurosis.”
PTSD has recently gained attention as a means of legal defense. As a defense, it may exist separately from “innocence by reason of insanity.” The authors review the literature, provide case vignettes exemplifying the clinical features, and present three additional cases that gained local and national notoriety because of their defense motions. The senior author served as an expert witness in these cases. Recommendations are given to readers who may in the future serve as expert witnesses or consultants in similar cases.
The nucleus accumbens (NAC) is a functionally heterogeneous brain region with respect to its involvement in cocaine-seeking behavior triggered by drug-associated explicit conditioned stimuli, foot shock stress, or cocaine itself in the reinstatement animal model of drug relapse. However, it is not known whether the NAC or its subregions are critical for reinstatement of cocaine-seeking behavior produced by re-exposure to a previously cocaine-paired environmental context.
The present study was designed to evaluate potentially unique contributions of the NAC core and shell to this behavior.
Materials and methods
Rats were trained to lever press for unsignaled cocaine infusions (0.15 mg/infusion, intravenous) in a distinct environmental context. Lever responding was then extinguished in a distinctly different environmental context (extinction context) during a minimum of seven daily training sessions. Subsequently, using a counterbalanced testing design, rats were re-exposed to the cocaine-paired context or the extinction context while cocaine seeking (i.e., responding on the previously cocaine-reinforced lever) was assessed. Before each test session, neural activity was inhibited selectively in the NAC core or shell using bilateral microinfusions of the γ-aminobutyric acid agonists, baclofen and muscimol (0/0 or 1.0/0.1 mM; 0.3 μl per hemisphere).
Neural inactivation of the NAC shell or core attenuated responding in the cocaine context and, interestingly, increased responding in the extinction context. Control experiments indicated no effects on general activity or food-reinforced instrumental behavior.
These findings suggest that both subregions of the NAC may promote context-induced reinstatement by facilitating drug context-induced motivation for cocaine and context discrimination.
Self-administration; Extinction; Reinstatement; Context; cocaine; Muscimol; Baclofen; Nucleus accumbens
This article examines the career of pioneer British psychoanalyst David Eder (1865–1936). Credited by Freud as the first practising psychoanalyst in England, active in early British socialism and then a significant figure in Zionism in post-war Palestine, and in between an adventurer in South America, a pioneer in the field of school medicine, and a writer on shell-shock, Eder is a strangely neglected figure in existing historiography. The connections between his interest in medicine, psychoanalysis, socialism and Zionism are also explored. In doing so, this article contributes to our developing understanding of the psychoanalytic culture of early twentieth-century Britain, pointing to its shifting relationship to broader ideology and the practical social and political challenges of the period. The article also reflects on the challenges for both Eder’s contemporaries and his biographers in making sense of such a life.
Psychoanalysis; Medicine; Socialism; Zionism; Palestine; South America; Biography; Kropotkin; Mental Deficiency; New Age; Children; Shell-Shock
The term posttraumatic stress disorder (PTSD) has become a household name since its first appearance in 1980 in the third edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-lll) purblished by the American Psychiatric Association, In the collective mind, this diagnosis is associated with the legacy of the Vietnam War disaster. Earlier conflicts had given birth to terms, such as “soldier's heart, ” “shell shock,” and “war neurosis.” The latter diagnosis was equivalent to the névrose de guerre and Kriegsneurose of French and German scientific literature. This article describes how the immediate and chronic consequences of psychological trauma made their way into medical literature, and how concepts of diagnosis and treatment evolved over time.
posttraumatic stress disorder; shell shock: psychotraumatology; literature; history of medicine
This article reviews the treatment of functional neurological symptoms during World War I
by Lewis Yealland at the National Hospital for the Paralysed and Epileptic in London.
Yealland was among the first doctors in Britain to incorporate electricity in the
systematic treatment of shell shock. Our analysis is based on the original case records of
his treatment of 196 soldiers with functional motor and sensory symptoms, functional
seizures and somatoform disorders. Yealland’s treatment approach integrated
peripheral and central electrical stimulation with a variety of other—psychological
and physical—interventions. A combination of electrical stimulation of affected
muscles with suggestion of imminent improvement was the hallmark of his approach. Although
his reported success rates were high, Yealland conducted no formal follow-up. Many of the
principles of his treatment, including the emphasis on suggestion, demonstration of
preserved function and the communication of a physiological illness model, are encountered
in current therapeutic approaches to functional motor and sensory symptoms. Yealland has
been attacked for his use of electrical stimulation and harsh disciplinary procedures in
popular and scientific literature during and after World War I. This criticism reflects
changing views on patient autonomy and the social role of doctors and directly impacts on
current debates on ethical justification of suggestive therapies. We argue that knowledge
of the historical approaches to diagnosis and management of functional neurological
syndromes can inform both aetiological models and treatment concepts for these challenging
war; electrotherapy; history; psychogenic; movement disorders
This paper concerns the potential use of compounds, including lipid A, chitosan, and carrageenan, from marine sources as agents for treating endotoxemic complications from Gram-negative infections, such as sepsis and endotoxic shock. Lipid A, which can be isolated from various species of marine bacteria, is a potential antagonist of bacterial endotoxins (lipopolysaccharide (LPSs)). Chitosan is a widespread marine polysaccharide that is derived from chitin, the major component of crustacean shells. The potential of chitosan as an LPS-binding and endotoxin-neutralizing agent is also examined in this paper, including a discussion on the generation of hydrophobic chitosan derivatives to increase the binding affinity of chitosan to LPS. In addition, the ability of carrageenan, which is the polysaccharide of red alga, to decrease the toxicity of LPS is discussed. We also review data obtained using animal models that demonstrate the potency of carrageenan and chitosan as antiendotoxin agents.
sepsis; endotoxin; endotoxin antagonists; lipid A; chitosan; carrageenan
Shell exchanges between hermit crabs may occur after a period of shell rapping, when the initiating or attacking crab brings its shell rapidly and repeatedly into contact with the shell of the non-initiator or defender, in a series of bouts. There are two opposing models of hermit crab shell exchange and the function of shell rapping. The negotiation model views shell exchange as a mutualistic activity, in which the initiator supplies information about the quality of its shell via the fundamental frequency of the rapping sound. The aggression model views shell rapping as either detrimental to the defending crab, or as providing it with information about the initiator's ability or motivation to continue, or both. The negotiation model makes no predictions about the temporal pattern of rapping, but under the aggression model it would be expected that crabs that rapped more vigorously would be more likely to effect an exchange. Repeating the signal could be expected under either model. Crabs that achieve an exchange rap more vigorously, rapping is more persistent when a clear gain in shell quality may be achieved, and the vigour is greater when the relative resource-holding potential (or 'fighting ability') is high. These findings support the aggression model rather than the negotiation model. Contrary to the predictions of game theory, crabs that do not effect an exchange appear to signal that they are about to give up. The data suggest that rapping is performed repeatedly because the accumulation of all of the performances acts as a signal of stamina.
The morphological variety displayed by the molluscan shell underlies much of the evolutionary success of this phylum. However, the broad diversity of shell forms, sizes, ornamentations and functions contrasts with a deep conservation of early cell movements associated with the initiation of shell construction. This process begins during early embryogenesis with a thickening of an ectodermal, ‘dorsal’ (opposite the blastopore) population of cells, which then invaginates into the blastocoel to form the shell gland. The shell gland evaginates to form the shell field, which then expands and further differentiates to eventually become the adult shell-secreting organ commonly known as the mantle. Despite the deep conservation of the early shell forming developmental program across molluscan classes, little is known about the fine-scale cellular or molecular processes that underlie molluscan shell development.
Using modern imaging techniques we provide here a description of the morphogenesis of a gastropod shell gland and shell field using the pulmonate gastropod Lymnaea stagnalis as a model. We find supporting evidence for a hypothesis of molluscan shell gland specification proposed over 60 years ago, and present histochemical assays that can be used to identify a variety of larval shell stages and distinct cell populations in whole mounts.
By providing a detailed spatial and temporal map of cell movements and differentiation events during early shell development in L. stagnalis we have established a platform for future work aimed at elucidation of the molecular mechanisms and regulatory networks that underlie the evo-devo of the molluscan shell.
Shell; Mollusc; Biomineralisation; Evolution; Development; Specification; Mantle; Alkaline phosphatase; Peroxidase
One of the most spectacular evolutionary forces is predation, evidenced to stimulate polymorphism in many prey species. Shell colour polymorphism of the land snail Cepaea nemoralis is a well-known model in evolutionary research. Nevertheless, the knowledge on the ecological causes driving its evolution remains incomplete and proximal factors shaping predatory pressure on C. nemoralis morphs are unknown. We evaluated shell crushing resistance and thickness, constituting crucial snail anti-predator defences in two shell areas (the apex and labium) of eight C. nemoralis morphotypes differing in shell colour and banding pattern. A GLM showed a significant effect of shell colour, banding pattern and shell thickness on shell strength. Pink shells were stronger than yellow ones, and banded forms had stronger shells than unbanded snails. The labium (usually attacked by mice) was generally thicker and more resistant than the apex (usually crushed by birds). Thicker shells were more resistant to crushing, and the rate of shell strength increase per unit of shell thickness was greater in pink and banded individuals compared to yellow and unbanded ones. Yellow and unbanded morphs have been found to be preferred by mice in the previous studies, which suggests that shell strength may be an important trait used in prey selection by these shell-crushing predators. The differences in potential anti-predator defences among snail morphs, found in the present study, justify future research on direct effect of C. nemoralis morphs shell strength on predator selectivity.
Polymorphism; Shell crushing resistance; Labium; Banding type
In this article, we reported the near-field interactions between the Ru(bpy)32+ complexes and plasmon resonances from the bimetallic nanoshells. The metallic nanoshells were fabricated on 20 nm silica spheres as cores by depositing 10 nm monometallic or bimetallic shells. There were approx. 15 Ru(bpy)32+ complexes in the silica core. The metal shells were constituted of silver or/and gold. The bimetallic shells could be generated in homogeneous or heterogeneous geometries. The homogeneous bimetallic shells contained 10 nm silver-gold alloys. The heterogeneous bimetallic shells contained successive 5 nm gold and 5 nm silver shells, or alternatively, 5 nm silver and 5 nm gold shells. Optical properties of metal nanoshells were studied on both the ensemble spectra and single nanoparticle imaging measurements. The heterogeneous bimetallic shells were found to have a large scale of metal-enhanced emission relative to the monometallic or homogeneous bimetallic shells. It is because the heterogeneous bimetallic shells may display split dual plasmon resonances which can interact with the excitation and emission bands of the Ru(bpy)32+ complexes in the silica cores leading to more efficient near-field interactions. The prediction can be demonstrated by the lifetimes. Therefore, it is suggested that both the compositions and geometries of the metal shells can influence the interactions with the fluorophores in the cores. This observation also offers us an opportunity for developing plasmon-based fluorescence metal nanoparticles as novel nanoparticle imaging agents which have high performances in fluorescence cell or tissue imaging.
fluorescence; bimetallic nanoshell; plasmon resonance; Ru(bpy)32+ complexes; optical properties of single nanoparticle; time-resolved confocal microscope; and near-field interaction
Ecophenotypes reflect local matches between organisms and their environment, and show plasticity across generations in response to current living conditions. Plastic responses in shell morphology and shell growth have been widely studied in gastropods and are often related to environmental calcium availability, which influences shell biomineralisation. To date, all of these studies have overlooked micro-scale structure of the shell, in addition to how it is related to species responses in the context of environmental pressure. This study is the first to demonstrate that environmental factors induce a bi-modal variation in the shell micro-scale structure of a land gastropod. Notodiscus hookeri is the only native land snail present in the Crozet Archipelago (sub-Antarctic region). The adults have evolved into two ecophenotypes, which are referred to here as MS (mineral shell) and OS (organic shell). The MS-ecophenotype is characterised by a thick mineralised shell. It is primarily distributed along the coastline, and could be associated to the presence of exchangeable calcium in the clay minerals of the soils. The Os-ecophenotype is characterised by a thin organic shell. It is primarily distributed at high altitudes in the mesic and xeric fell-fields in soils with large particles that lack clay and exchangeable calcium. Snails of the Os-ecophenotype are characterised by thinner and larger shell sizes compared to snails of the MS- ecophenotype, indicating a trade-off between mineral thickness and shell size. This pattern increased along a temporal scale; whereby, older adult snails were more clearly separated into two clusters compared to the younger adult snails. The prevalence of glycine-rich proteins in the organic shell layer of N. hookeri, along with the absence of chitin, differs to the organic scaffolds of molluscan biominerals. The present study provides new insights for testing the adaptive value of phenotypic plasticity in response to spatial and temporal environmental variations.
Many groups of land snails show great interspecific diversity in shell ornamentation, which may include spines on the shell and flanges on the aperture. Such structures have been explained as camouflage or defence, but the possibility that they might be under sexual selection has not previously been explored.
Presentation of the hypothesis
The hypothesis that is presented consists of two parts. First, that shell ornamentation is the result of sexual selection. Second, that such sexual selection has caused the divergence in shell shape in different species.
Testing the hypothesis
The first part of the hypothesis may be tested by searching for sexual dimorphism in shell ornamentation in gonochoristic snails, by searching for increased variance in shell ornamentation relative to other shell traits, and by mate choice experiments using individuals with experimentally enhanced ornamentation. The second part of the hypothesis may be tested by comparing sister groups and correlating shell diversity with degree of polygamy.
Implications of the hypothesis
If the hypothesis were true, it would provide an explanation for the many cases of allopatric evolutionary radiation in snails, where shell diversity cannot be related to any niche differentiation or environmental differences.