FIELD EVIDENCE FOR DENSITY-DEPENDENT EFFECTS IN THE TREMATODE MICROPHALLUS PAPILLOROBUSTUS IN ITS MANIPULATED HOST, GAMMARUS INSENSIBILIS

Numerous studies have demonstrated that parasites with complex life cycles frequently manipulate the phenotype of their hosts to increase their transmission rate. Little is known, however, concerning density-dependent processes within infrapopulations of manipulative parasites--whether parasites cooperate to manipulate the host, whether competition counteracts with these potential cooperative benefits, or both. Here we explored these ideas, focusing on the association between the manipulative trematode Microphallus papillorobustus and its second intermediate host, the gammarid Gammarus insensibilis. From the data collected in the field, we found no evidence that co-occurring M. papillorobustus individuals benefit from the presence of conspecifics; instead, individuals in larger infrapopulations suffered reduced size and fecundity. Thus, the net effect of increasing density suggests that competition rather than cooperation is the dominant force in infrapopulations of M. papillorobustus.

Host manipulation by Ligula intestinalis: a cause or consequence of parasite aggregation?

Previous investigations suggest that the infection of the cyprinid roach, Rutilus rutilus, with the larval plerocercoid forms of the cestode, Ligula intestinalis, creates behavioural and morphological changes in the fish host, potentially of adaptive significance to the parasite in promoting transmission to definitive avian hosts. Here we consider whether these behavioural changes are important in shaping the distribution of parasite individuals across the fish population. An examination of field data illustrates that fish infected with a single parasite were more scarce than expected under the negative binomial distribution, and in many months were more scarce than burdens of two, three or more, leading to a bimodal distribution of worm counts (peaks at 0 and >1). This scarcity of single-larval worm infections could be accounted for a priori by a predominance of multiple infection. However, experimental infections of roach gave no evidence for the establishment of multiple worms, even when the host was challenged with multiple intermediate crustacean hosts, each multiply infected. A second hypothesis assumes that host manipulation following an initial single infection leads to an increased probability of subsequent infection (thus creating a contagious distribution). If manipulated fish are more likely to encounter infected first-intermediate hosts (through microhabitat change, increased ingestion, or both), then host manipulation could act as a powerful cause of aggregation. A number of scenarios based on contagious distribution models of aggregation are explored, contrasted with alternative compound Poisson models, and compared with the empirical data on L. intestinalis aggregation in their roach intermediate hosts. Our results indicate that parasite-induced host manipulation in this system can function simultaneously as both a consequence and a cause of parasite aggregation. This mutual interaction between host manipulation and parasite aggregation points to a set of ecological interactions that are easily missed in most experimental studies of either phenomenon.

Determining hydrogen-bond strengths in the solid state by NMR: the quantitative measurement of homonuclear J couplings

Hydrogen-bonding strengths in the solid state are quantitatively determined by the accurate measurement of 15N-15N J couplings using a straightforward 2D MAS NMR spinecho approach.

An unlikely partnership: parasites, concomitant immunity and host defence

Concomitant immunity (CI) against macroparasites describes a state of effective anti-larval immunity coupled with persistent adult infection. Experimental studies indicate that immunologically concealed adult worms might promote anti-larval immunity via the release of cross-reactive antigens, thus creating a barrier against continual infection and restricting burden size within the host. CI offers an important potential benefit to established worms by preventing overcrowding within the host. Thus, CI may be interpreted as akin to vaccination; relatively long-lived adult worms 'vaccinate' their host with larval surface antigens and so benefit from reduced conspecific competition. The shared responsibility for host vaccination among adult worms leads to a problem of collective action. Here, we build on earlier analytical findings about the evolutionary forces that shape cooperation among parasites in order to produce a stochastic simulation model of macroparasite social evolution. First, we theoretically investigate a parasite adaptation hypothesis of CI and demonstrate its plausibility under defined conditions, despite the possibility of evolutionary 'cheats'. Then we derive a set of predictions for testing the hypothesis that CI is partly a host-manipulative parasite adaptation. Evidence in support of this model would present an unusual case of adaptive population regulation.

Host manipulation by Ligula intestinalis: accident or adaptation?

Numerous studies have demonstrated that parasites with complex life-cycles can cause phenotypic modifications in their hosts that lead to an increased rate of transmission, and suggest that these modifications are the result of parasitic adaptations to manipulate the host. Little attention is paid, however, to separating the possibility of adaptive host manipulation from incidental (if fortuitous) side-effects of infection. In this study we combine statistical and analytical tools to interpret the impact of the macroparasite Ligula intestinalis L. (Cestoda, Pseudophyllidea) on the behaviour of its intermediate fish host (the roach, Rutilus rutilus L.), using field data on a natural system. Two distinct sets of generalized linear models agree that both the presence and the intensity of infection contribute to a modified behavioural response in the host. This was illustrated by a preference for the lake-edge in infected fish during autumn. Furthermore, the effect of parasites upon their host is heterogeneous with respect to parasite size, with larger parasite individuals having a disproportionate impact. A series of game-theoretic models of adaptive host manipulation illustrate a potential rationale for a size-dependent manipulation strategy in parasites. These findings illustrate the potential complexity and functionality of the impact of L. intestinalis upon its fish host, which together reduce the parsimony of the alternative 'incidental effect' hypothesis.

Cooperation in the dark: signalling and collective action in quorum-sensing bacteria

The study of quorum-sensing bacteria has revealed a widespread mechanism of coordinating bacterial gene expression with cell density. By monitoring a constitutively produced signal molecule, individual bacteria can limit their expression of group-beneficial phenotypes to cell densities that guarantee an effective group outcome. In this paper, we attempt to move away from a commonly expressed view that these impressive feats of coordination are examples of multicellularity in prokaryotic populations. Here, we look more closely at the individual conflict underlying this cooperation, illustrating that, even under significant levels of genetic conflict, signalling and resultant cooperative behaviour can stably exist. A predictive two-trait model of signal strength and of the extent of cooperation is developed as a function of relatedness (reflecting multiplicity of infection) and basic population demographic parameters. The model predicts that the strength of quorum signalling will increase as conflict (multiplicity of infecting strains) increases, as individuals attempt to coax more cooperative contributions from their competitors, leading to a devaluation of the signal as an indicator of density. Conversely, as genetic conflict increases, the model predicts that the threshold density for cooperation will increase and the subsequent strength of group cooperation will be depressed.

Self-efficacy as a moderator of information-seeking effectiveness

The authors assessed previously unexplored processes by which information seeking and self-efficacy contribute to self-regulatory effectiveness in industrial selling. They assessed the synergistic interaction of inquiry and monitoring with respect to role clarity and tested whether this interaction was further moderated by self-efficacy. Results indicated that the role-clarifying effects of feedback inquiry and monitoring were contingent rather than independent. Role clarity increased as the combination of inquiry and monitoring increased. Furthermore, these joint effects were moderated by self-efficacy, such that high-self-efficacy employees were able to effectively use the combination of inquiry and monitoring to clarify role expectations, whereas low-self-efficacy employees were not. Implications for theory, practice, and future research are discussed.

Phenotypic modification of roach (Rutilus rutilus L.) infected with Ligula intestinalis L. (Cestoda: Pseudophyllidea)

In European freshwater, cyprinid fish may be heavily infected by plerocercoids of the pseudophyllidea cestode Ligula intestinalis (L.). During their development, these parasites grow rapidly to a large size in the fish's body cavity, characteristically distending the abdomen. In this study, the influence of this tapeworm on roach (Rutilus rutilus L.) morphology was analyzed. Forty-five infected and 45 uninfected roach were collected from the Lavernose-Lacasse gravel pit in Toulouse, south western France and examined for 40 morphological measurements to study phenotypic modification of the body and 14 bilateral characters for an analysis of asymmetry. Results indicate that the degree of bilateral asymmetry does not change between infected and uninfected roach, despite the strong host-morphological modifications such as deformation of the abdomen, fin displacements at the level of the tail, and sagging of the vertebral column. The intensity of abdominal distension and fish morphology changes depends on the total parasite biomass present. Differences were observed in morphology at different levels of infection, which relate to established effects of L. intestinalis on the physiology and behavior of intermediate hosts. These morphological changes induced by the parasite could increase trophic transmission to the definitive avian hosts.

Autumn tree colours as a handicap signal

Many species of deciduous trees display striking colour changes in autumn. Here, we present a functional hypothesis: bright autumn coloration serves as an honest signal of defensive commitment against autumn colonizing insect pests. According to this hypothesis, individuals within a signalling species show variation in the expression of autumn coloration, with defensively committed trees producing a more intense display. Insects are expected to be averse to the brightest tree individuals and, hence, preferentially colonize the least defensive hosts. We predicted that tree species suffering greater insect damage would, on average, invest more in autumn-colour signalling than less troubled species. Here, we show that autumn coloration is stronger in species facing a high diversity of damaging specialist aphids. Aphids are likely to be an important group of signal receivers because they are choosy, damaging and use colour cues in host selection. In the light of further aspects of insect and tree biology, these results support the notion that bright autumn colours are expensive handicap signals revealing the defensive commitment of individual trees to autumn colonizing insect pests.

An investigation of the hydrogen-bonding structure in bilirubin by 1H double-quantum magic-angle spinning solid-state NMR spectroscopy

The complex hydrogen-bonding arrangement in the biologically important molecule bilirubin IXalpha is probed by using 1H double-quantum (DQ) magic-angle spinning (MAS) NMR spectroscopy. Employing fast MAS (30 kHz) and a high magnetic field (16.4 T), three low-field resonances corresponding to the different hydrogen-bonding protons are resolved in a 1H MAS NMR spectrum of bilirubin. These resonances are assigned on the basis of the proton-proton proximities identified from a two-dimensional rotor-synchronized 1H DQ MAS NMR spectrum. An analysis of 1H DQ MAS spinning-sideband patterns for the NH protons in bilirubin allows the quantitative determination of proton-proton distances and the geometry. The validity of this procedure is proven by simulated spectra for a model three-spin system, which show that the shortest distance can be determined to a very high degree of accuracy. The distance between the lactam and pyrrole NH protons in bilirubin is determined to be 0.186 +/- 0.002 nm (corresponding to a dominant dipolar coupling constant of 18.5 +/- 0.5 kHz). The analysis also yields a distance between the lactam NH and carboxylic acid OH protons of 0.230 +/- 0.008 nm (corresponding to a perturbing dipolar coupling constant of 9.9 +/- 1.0 kHz) and an H-H-H angle of 122 +/- 4 degrees. Finally, a comparison of 1H DQ MAS spinning-sideband patterns for bilirubin and its dimethyl ester reveals a significantly longer distance between the two NH protons in the latter case.

Structure assignment in the solid state by the coupling of quantum chemical calculations with NMR experiments: a columnar hexabenzocoronene derivative

We present a quantum chemical ab initio study which demonstrates a new combined experimental and theoretical approach, whereby a comparison of calculated and experimental (1)H NMR chemical shifts allows the elucidation of structural arrangements in solid-state molecular ensembles, taking advantage of the marked sensitivity of the (1)H chemical shift to intermolecular interactions. Recently, Brown et al. have shown that, under fast magic-angle spinning (MAS) at 35 kHz, the resolution in a (1)H NMR spectrum of the solid phase of an alkyl-substituted hexabenzocoronene (HBC) derivative is sufficient to observe the hitherto unexpected resolution of three distinct aromatic resonances ( J. Am. Chem. Soc. 1999, 121, 6712). Exploiting the additional information about proton proximities provided by (1)H double-quantum (DQ) MAS NMR spectroscopy, it was shown that the results are qualitatively consistent with the aromatic cores packing in a manner similar to that in unsubstituted HBC. Using the HBC-C(12) molecule as an example, we show here that the new combined experimental and theoretical approach allows the observed (1)H chemical shifts to be related in a quantitative manner to the intermolecular structure. In the quantum chemical calculations, a series of model systems of stacked HBC oligomers are used. On account of the marked dependence of the (1)H chemical shift to ring currents arising from nearby aromatic rings, the calculated (1)H chemical shifts are found to be very sensitive to the stacking arrangement of the HBC molecules. Moreover, the ring current effect is found to be particularly long range, with a considerable influence of the second neighbor, at a distance of 700 pm, being observed.

Spatial scale and cellular substrate of contrast adaptation by retinal ganglion cells

Human visual perception and many visual system neurons adapt to the luminance and contrast of the stimulus. Here we describe a form of contrast adaptation that occurs in the retina. This adaptation had a local scale smaller than the dendritic or receptive fields of single ganglion cells and was insensitive to pharmacological manipulation of amacrine cell function. These results implicate the bipolar cell pathway as a site of contrast adaptation. The time required for contrast adaptation varied with stimulus size, ranging from approximately 100 ms for the smallest stimuli, to seconds for stimuli the size of the receptive field. The differing scales and time courses of these effects suggest that multiple types of contrast adaptation are used in viewing natural scenes.

An integrated model of feedback-seeking behavior: disposition, context, and cognition

This study replicates, integrates, and extends prior research on the dispositional, contextual, and cognitive antecedents of feedback-seeking behavior. Regression analysis was used to analyze data collected from a sample of salespeople (N = 310) from 2 Fortune 500 companies. The study hypotheses were supported with the following results. First, the individual disposition of learning goal orientation and the contextual factors of leader consideration and leader initiation of structure influenced cognitions about the perceived cost and value of feedback seeking. Second, the strength of the relationship of learning goal orientation with the cost and value perceptions was moderated by the leadership style of the supervisor.

Receptive field microstructure and dendritic geometry of retinal ganglion cells

We studied the fine spatial structure of the receptive fields of retinal ganglion cells and its relationship to the dendritic geometry of these cells. Cells from which recordings had been made were microinjected with Lucifer yellow, so that responses generated at precise locations within the receptive field center could be directly compared with that cell's dendritic structure. While many cells with small receptive fields had domeshaped sensitivity profiles, the majority of large receptive fields were composed of multiple regions of high sensitivity. The density of dendritic branches at any one location did not predict the regions of high sensitivity. Instead, the interactions between a ganglion cell's dendritic tree and the local mosaic of bipolar cell axons seem to define the fine structure of the receptive field center.

Role of laparoscopic ultrasonography in the management of patients with oesophagogastric cancer

BACKGROUND

Laparoscopy and laparoscopic ultrasonography (lapUS) have been shown to improve the staging of patients with oesophagogastric cancer but there remains doubt as to whether most benefit follows laparoscopy alone and how much is contributed by the addition of lapUS.

METHODS

The role of lapUS in surgical decision making was evaluated prospectively in a consecutive series of patients with oesophagogastric cancer following conventional radiological assessment. The results of the lapUS findings over and above the laparoscopic findings were documented in order to identify the additional benefit of lapUS.

RESULTS

After initial conventional assessment 41 patients were considered unsuitable for surgery and treated by palliation, with a further 25 patients proceeding to surgery without laparoscopy. Of the 93 patients who underwent laparoscopy, 18 were shown to have irresectable disease and avoided further surgery; a further seven avoided inappropriate surgery by the addition of lapUS. The open-close laparotomy rate was reduced from five of 25 in patients who did not undergo laparoscopy to nine (12 per cent) of 75 by the introduction of laparoscopy and to two (3 per cent) of 68 with the addition of lapUS.

CONCLUSION

Laparoscopy alone prevented unnecessary surgery in 18 (19 per cent) of 93 patients with oesophagogastric cancer and the addition of lapUS identified a further seven patients (8 per cent) in whom unnecessary surgery was avoided.

Consultant surgeons' opinion of the skills required of basic surgical trainees

BACKGROUND

Accurate and appropriate assessment of surgical trainees requires clear determination of the skills needed for surgical competence. This study was designed to identify those skills, rank them in order of importance and translate them into behavioural terms.

METHODS

A Delphi technique, using anonymous postal questionnaires, was used. All consultant surgeons in South-East Scotland were asked to identify the skills they expected of surgical trainees. Skills identified were then returned to all consultants for weighting. Differences among specialties in the importance of each item were identified using analysis of variance.

RESULTS

The qualities identified fell into five domains: technical skills, clinical skills, interaction with patients and relatives, teamwork, and application of knowledge. Consultants from all specialties gave high weightings to the generic domains of clinical skills, teamwork, and interaction with patients and relatives.

CONCLUSION

This study has identified the skills considered necessary by consultant surgeons in Scotland for a successful surgical career. Contrary to expectation, consultant surgeons value many generic skills more highly than technical skills, indicating that they value well rounded doctors, not just those with technical ability. The characteristics identified are being used to develop an assessment tool for use on basic surgical trainees.

Costratification of a population of bipolar cells with the direction-selective circuitry of the rabbit retina

We have stained a new population of bipolar cells in rabbit retina by using antibodies against the carbohydrate epitope, CD15. The CD15-positive bipolar cells comprise 6-8% of the total cone bipolar cells in peripheral retina. Their axonal and dendritic arbors are similar in size and range from 15 to 50 pm in diameter. The axonal arbors are narrowly stratified in sublamina b of the inner plexiform layer. Double label experiments using an antibody against the calcium binding protein, calbindin, or an antibody against protein kinase C, demonstrate that the CD15-positive bipolar cells are a separate population from the previously identified calbindin-positive cone bipolar cells and the rod bipolar cells. Labeling the processes of starburst amacrine cells with antibodies against choline acetyltransferase showed that the CD15-positive bipolar cells stratify within and slightly more distally to the processes of the ON-starburst amacrine cells. Confocal images of retinal wholemounts showed that the axons of the CD15-positive bipolar cells follow the pattern of the ON-starburst cells' processes. Axonal varicosities of the CD15-positive bipolar cells penetrate the bundles formed by the processes of the ON-starburst cells. This finding suggests that the CD15-positive bipolar cell provides input to the ON-starburst amacrine cells and/or the ON-plexus of the ON-OFF direction-selective ganglion cells.

Incidence of cranial ultrasound abnormalities in apparently well neonates on a postnatal ward: correlation with antenatal and perinatal factors and neurological status

AIM

To evaluate cranial ultrasonography and neurological examination in a cohort of infants regarded as normal; and to determine the prevalence of ultrasound abnormalities and any potential association with antenatal or perinatal factors or deviant neurological signs.

METHODS

Cranial ultrasound findings and neurological status were evaluated in 177 newborns (gestational age 36.3 to 42 weeks), admitted to a postnatal ward directly after birth and regarded as normal by obstetric and paediatric staff. The age of the infants at the time of examination ranged between 6 and 48 hours. Ultrasound abnormalities were present in 35 of the 177 infants studied (20%). Ischaemic lesions, such as periventricular and thalamic densities were the most common finding (8%), followed by haemorrhagic lesions (6%). The possible sequelae of antenatal haemorrhages, such as focal ventricular dilatation or choroid cysts, were present in 6%. Abnormal ultrasound findings were not significantly associated with signs of perinatal distress, such as cardiotocographic abnormalities or passage of meconium. Abnormal ultrasound findings tended to be associated with antenatal problems, although this did not reach significance. Ultrasound abnormalities were strongly associated with deviant patterns on the neurological examination.

CONCLUSIONS

These results suggest that ultrasound abnormalities are more common than has been reported up to now. Lesions that could be ischaemic, such as flare densities, are seen even in the absence of any antenatal or perinatal risk factor.

Pathological versus physiological left ventricular hypertrophy: a review

Left ventricular hypertrophy is recognized as an independent risk factor for cardiovascular morbid events. The primary mechanisms responsible for stimulating it are unknown. Epidemiological theories suggest that left ventricular hypertrophy is a continuous variable with no threshold, while morphological studies argue that it is the structure, or quality, and function of the myocardium (and therefore non-continuous), not the quantity of the myocardial mass, that poses the cardiovascular risk. Although left ventricular hypertrophy has been classically viewed as an adaptive response of the cardiovascular system to an imposed load, it has been demonstrated that haemodynamic overloading in selected hypertensive patients is not the sole determinant of left ventricular structure and function. Pathological and physiological states of left ventricular hypertrophy have been described primarily using criteria focusing on normal chamber performance and oxygen delivery as well as the reversibility of the hypertrophy once the overload is removed. Both states are also defined by the nature of the imposed load and the resulting myocardial adaptations. This review addresses the pathological and physiological states of left ventricular hypertrophy, the hypertrophy patterns, and the corresponding structural and functional characteristics, together with some of the biochemical factors thought to influence remodelling.

Breakthrough bacteremia and meningitis during treatment with cephalosporins parenterally for pneumococcal pneumonia

An extended-spectrum cephalosporin has been considered appropriate therapy for non-meningeal infections caused by drug-resistant Streptococcus pneumoniae. We report a toddler who had breakthrough bacteremia and meningitis develop because of drug-resistant pneumococcus while receiving treatment with cefotaxime and cefuroxime for pneumonia.