bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Template for a Voltage Sensor in a Novel K+ Channel. II. Conservation of a Eukaryotic Sensor Fold in a Prokaryotic K+ Channel
Authors: Lundby Alicia , Santos Jose S. , Zazueta Cecilia , Montal Mauricio
Published: August 2006

KvLm, a novel bacterial depolarization-activated K+ (Kv) channel isolated from the genome of Listeria monocytogenes, contains a voltage sensor module whose sequence deviates considerably from the consensus sequence of a Kv channel sensor in that only three out of eight conserved charged positions are present. Surprisingly, KvLm exhibits the steep dependence of the open channel probability on membrane potential that is characteristic of eukaryotic Kv channels whose sensor sequence approximates the consensus. Here we asked if the KvLm sensor shared a similar fold to that of Shaker, the archetypal eukaryotic Kv channel, by examining if interactions between conserved residues in Shaker known to mediate sensor biogenesis and function were conserved in KvLm. To this end, each of the five non-conserved residues in the KvLm sensor were mutated to their Shaker-like charged residues, and the impact of these mutations on the voltage dependence of activation was assayed by current recordings from excised membrane patches of Escherichia coli spheroplasts expressing the KvLm mutants. Conservation of pairwise interactions was investigated by comparison of the effect of single mutations to the impact of double mutations presumed to restore wild-type fold and voltage sensitivity. We observed significant functional coupling between sites known to interact in Shaker Kv channels, supporting the notion that the KvLm sensor largely retains the fold of its eukaryotic homologue.
A Randomized Controlled Trial of Tai Chi for Tension Headaches
Authors: Abbott Ryan B. , Hui Ka-Kit , Hays Ron D. , Li Ming-Dong , Pan Timothy
Published: August 2006

This study examined whether a traditional low‐impact mind–body exercise, Tai Chi, affects health‐related quality‐of‐life (HRQOL) and headache impact in an adult population suffering from tension‐type headaches. Forty‐seven participants were randomly assigned to either a 15 week intervention program of Tai Chi instruction or a wait‐list control group. HRQOL (SF‐36v2) and headache status (HIT‐6™) were obtained at baseline and at 5, 10 and 15 weeks post‐baseline during the intervention period. Statistically significant (P < 0.05) improvements in favor of the intervention were present for the HIT score and the SF‐36 pain, energy/fatigue, social functioning, emotional well‐being and mental health summary scores. A 15 week intervention of Tai Chi practice was effective in reducing headache impact and also effective in improving perceptions of some aspects of physical and mental health.
The influence of social affiliation on individual vocal signatures of northern resident killer whales (
Orcinus orca
)
Authors: Nousek Anna E , Slater Peter J.B , Wang Chao , Miller Patrick J.O
Published: August 2006

Northern resident killer whales (
Orcinus orca
) live in highly stable groups and use group-specific vocal signals, but individual variation in calls has not been described previously. A towed beam-forming array was used to ascribe stereotyped pulsed calls with two independently modulated frequency contours to visually identified individual killer whales in Johnstone Strait, British Columbia. Overall, call similarity determined using neural networks differed significantly between different affiliation levels for both frequency components of all the call types analysed. This method distinguished calls from individuals within the same matriline better than different calls produced by a single individual and better than by chance. The calls of individuals from different matrilines were more distinctive than those within the same matriline, confirming previous studies based on group recordings. These results show that frequency contours of stereotyped calls differ among the individuals that are constantly associated with each other and use group-specific vocalizations, though across-group differences were substantially more pronounced.
Chimpanzee and felid diet composition is influenced by prey brain size
Authors: Shultz Susanne , Dunbar R.I.M
Published: August 2006

Prey use a wide variety of anti-predator defence strategies, including morphological and chemical defences as well as behavioural traits (risk-modulated habitat use, changes in activity patterns, foraging decisions and group living). The critical test of how effective anti-predator strategies are is to relate them to relative indices of mortality across predators. Here, we compare biases in predator diet composition with prey characteristics and show that chimpanzee (Pan troglodytes) and felid show the strongest and the most consistent predator bias towards small-brained prey. We propose that large-brained prey are likely to be more effective at evading predators because they can effectively alter their behavioural responses to specific predator encounters. Thus, we provide evidence for the hypothesis that brain size evolution is potentially driven by selection for more sophisticated and behaviourally flexible anti-predator strategies.
Contrasting patterns of sequence divergence and base composition betweenDrosophilaintrons and intergenic regions
Authors: Ometto Lino , De Lorenzo David , Stephan Wolfgang
Published: August 2006

Two non-coding DNA classes, introns and intergenic regions, ofDrosophila melanogasterexhibit contrasting evolutionary patterns. GC content is significantly higher in intergenic regions and affects their degree of nucleotide variability. Divergence is positively correlated with recombination rate in intergenic regions, but not in introns. We argue that these differences are due to different selective constraints rather than mutational or recombinational mechanisms.
Avian predators attack aposematic prey more forcefully when they are part of an aggregation
Authors: Skelhorn John , Ruxton Graeme D
Published: August 2006

Defended insects often advertise their unprofitability to potential predators using conspicuous aposematic coloration. Many aposematic insects are also gregarious, and it has been suggested that the aggregation of defended prey may have facilitated the evolution of aposematic coloration. Empirical studies have demonstrated that birds are more wary of aggregated aposematic prey, and learn to avoid them more quickly than solitary prey. However, many aposematic insects survive being attacked by birds, and the effect of aggregation on post-attack survival has not previously been investigated. Using domestic chicks as predators and artificially manipulated mealworms as prey, we provide empirical evidence that predators attack aggregated aposematic prey more forcefully than solitary prey, reducing the likelihood of prey surviving an attack. Hence, we suggest that previous works concluding that aggregation was an important pre-requisite for the evolution of aposematism may have overestimated the fitness benefits of aggregation, since aggregated prey may be attacked less but are also less likely to survive an attack.
Diversification of Neoaves: integration of molecular sequence data and fossils
Authors: Ericson Per G.P , Anderson Cajsa L , Britton Tom , Elzanowski Andrzej , Johansson Ulf S , Källersjö Mari , Ohlson Jan I , Parsons Thomas J , Zuccon Dario , Mayr Gerald
Published: August 2006

Patterns of diversification and timing of evolution within Neoaves, which includes almost 95% of all bird species, are virtually unknown. On the other hand, molecular data consistently indicate a Cretaceous origin of many neoavian lineages and the fossil record seems to support an Early Tertiary diversification. Here, we present the first well-resolved molecular phylogeny for Neoaves, together with divergence time estimates calibrated with a large number of stratigraphically and phylogenetically well-documented fossils. Our study defines several well-supported clades within Neoaves. The calibration results suggest that Neoaves, after an initial split from Galloanseres in Mid-Cretaceous, diversified around or soon after the K/T boundary. Our results thus do not contradict palaeontological data and show that there is no solid molecular evidence for an extensive pre-Tertiary radiation of Neoaves.
Consistent sex ratio bias of individual female dragon lizards
Authors: Uller Tobias , Mott Beth , Odierna Gaetano , Olsson Mats
Published: August 2006

Sex ratio evolution relies on genetic variation in either the phenotypic traits that influence sex ratios or sex-determining mechanisms. However, consistent variation among females in offspring sex ratio is rarely investigated. Here, we show that female painted dragons (
Ctenophorus pictus
) have highly repeatable sex ratios among clutches within years. A consistent effect of female identity could represent stable phenotypic differences among females or genetic variation in sex-determining mechanisms. Sex ratios were not correlated with female size, body condition or coloration. Furthermore, sex ratios were not influenced by incubation temperature. However, the variation among females resulted in female-biased mean population sex ratios at hatching both within and among years.
Extrafloral nectary phenotypic plasticity is damage- and resource-dependent inVicia faba
Authors: Mondor Edward B , Tremblay Michelle N , Messing Russell H
Published: August 2006

Phenotypic plasticity enables many damaged plants to increase nectar secretion rates from extrafloral nectaries (EFNs), or in the case of broad bean,Vicia fabaL., to produce additional EFNs, to attract natural enemies of herbivores. While plants benefit greatly from these defensive mutualisms, the costs of producing EFNs are largely unknown. We hypothesized that if EFN production is costly, then damaged plants with high resource levels would be able to produce more EFNs than plants that are resource-limited. Here, we show that this indirect inducible defence does follow this general pattern.Vicia fabaenriched with 6 or 12 g of 14 : 14 : 14 NPK fertilizer increased EFN numbers after leaf damage by 46 and 60%, respectively, compared with nutrient-poor plants. Thus, EFN production is both damage- and resource-dependent. Analogous to direct defences, production of EFNs may limit the overall loss of leaf tissue when risk of herbivory increases.
A novel obligate cultivation mutualism between damselfish andPolysiphoniaalgae
Authors: Hata Hiroki , Kato Makoto
Published: August 2006

In cultivation mutualisms, farming animals prepare fields for cultivars, enhance their growth and harvest them. For example, in terrestrial ecosystems, plant–herbivore cultivation mutualisms arose between humans and their crops only relatively recently. We discovered an obligate cultivation mutualism between a damselfish and an alga in a coral reef ecosystem. The damselfish,Stegastes nigricans, manages algal farms through territorial defence against the invading grazers and through weeding of unpalatable algae. As a result, the algal farms ofS. nigricansare dominated by one species,Polysiphoniasp. We performed an exhaustive survey of algal assemblages inside and outside the territories of five damselfish species around the Ryukyu Islands, Japan, using molecular and morphological characteristics.Polysiphoniasp. 1 grew exclusively inside the farms ofS. nigricans, and never elsewhere. Since onlyPolysiphoniasp. 1 is harvested and consumed by the damselfish as a staple food, this interdependent relationship is an obligate cultivation mutualism. This is the first record of an obligate plant–herbivore cultivation mutualism in a marine ecosystem. Our data also suggest that three otherPolysiphoniaspecies are facultatively mutual with, commensal with, or parasitic on other damselfish species.
Factors determining the potential for onward transmission of variant Creutzfeldt–Jakob disease via surgical instruments
Authors: Garske Tini , Ward Hester J.T , Clarke Paul , Will Robert G , Ghani Azra C
Published: August 2006

While the number of variant Creutzfeldt–Jakob disease (vCJD) cases continues to decline, concern has been raised that transmission could occur directly from one person to another through routes including the transfer of blood and shared use of surgical instruments. Here we firstly present data on the surgical procedures undertaken on vCJD patients prior to onset of clinical symptoms, which supports the hypothesis that cases via this route are possible. We then apply a mathematical framework to assess the potential for self-sustaining epidemics via surgical procedures. Data from hospital episode statistics on the rates of high- and medium-risk procedures in the UK were used to estimate model parameters, and sensitivity to other unknown parameters about surgically transmitted vCJD was assessed. Our results demonstrate that a key uncertainty determining the scale of an epidemic and whether it is self-sustaining is the number of times a single instrument is re-used, alongside the infectivity of contaminated instruments and the effectiveness of cleaning. A survey into the frequency of re-use of surgical instruments would help reduce these uncertainties.
Systems interface biology
Authors: Doyle Francis J , Stelling Jörg
Published: August 2006

The field of systems biology has attracted the attention of biologists, engineers, mathematicians, physicists, chemists and others in an endeavour to create systems-level understanding of complex biological networks. In particular, systems engineering methods are finding unique opportunities in characterizing the rich behaviour exhibited by biological systems. In the same manner, these new classes of biological problems are motivating novel developments in theoretical systems approaches. Hence, theinterfacebetween systems and biology is of mutual benefit to both disciplines.
Bioactive and bioresorbable cellular cubic-composite scaffolds for use in bone reconstruction
Authors: Shikinami Yasuo , Okazaki Kenshi , Saito Makoto , Okuno Masaki , Hasegawa Shin , Tamura Jiro , Fujibayashi Shunsuke , Nakamura Takashi
Published: August 2006

We used a novel composite fibre-precipitation method to create bioactive and bioresorbable cellular cubic composites containing calcium phosphate (CaP) particles (unsintered and uncalcined hydroxyapatite (u-HA), α-tricalcium phosphate, β-tricalcium phosphate, tetracalcium phosphate, dicalcium phosphate dihydrate, dicalcium phosphate anhydrate or octacalcium phosphate) in a poly-d/l-lactide matrix. The CaP particles occupied greater than or equal to 70 wt% (greater than or equal to 50 vol%) fractions within the composites. The porosities of the cellular cubic composites were greater than or equal to 70% and interconnective pores accounted for greater than or equal to 70% of these values.In vitrochanges in the cellular geometries and physical properties of the composites were evaluated over time. The Alamar Blue assay was used to measure osteoblast proliferation, while the alkaline phosphatase assay was used to measure osteoblast differentiation. Cellular cubic C-u-HA70, which contained 70 wt% u-HA particles in a 30 wt% poly-d/l-lactide matrix, showed the greatest three-dimensional cell affinity among the materials tested. This composite had similar compressive strength and cellular geometry to cancellous bone, could be modified intraoperatively (by trimming or heating) and was able to form cortico-cancellous bone-like hybrids. The osteoinductivity of C-u-HA70, independent of biological growth factors, was confirmed by implantation into the back muscles of beagles. Our results demonstrated that C-u-HA70 has the potential as a cell scaffold or temporary hard-tissue substitute for clinical use in bone reconstruction.
‘Morphing’ bistable orthotropic elliptical shallow shells
Authors: Seffen K.A
Published: August 2006

This study is concerned with the equilibrium shapes of orthotropic, elliptical plates and shells deforming elastically without initial stresses. The aim is to explore potential bistable configurations and their dependencies on material parameters and initial shape for elucidating novel morphing structures. A strain energy formulation gives way to a compact set of governing equations of deformation, which can be solved in closed form for some isotropic and orthotropic conditions. It is shown that bistability depends on the change in Gaussian curvature of the shell, in particular, for initially untwisted shells, isotropy precludes bistability, where there is negative initial Gaussian curvature, but orthotropic materials yield bistability irrespective of the sign of the initial Gaussian curvature. This improved range of performance stems from increasing the independent shear modulus, which imparts sufficient torsional rigidity to stabilize against perturbations in the deformed state. It is also shown that the range of bistable configurations for initially twisted shells generally diminishes as the degree of twist increases.
Solar position within Monet's Houses of Parliament
Authors: Baker Jacob , Thornes John E
Published: August 2006

Paintings from Monet's Houses of Parliament London series have been analysed for the quantitative information they contain, by comparing the depicted position of the Sun with Solar geometry calculations. The positions of roofline features of the Houses of Parliament were measured to provide an internal scale for the determination of azimuthal and elevation angles of the Solar depictions. Despite some distortion of the painted motif, the internal scales were found to be approximately linear. The Solar positions were used to derive the dates and times of the depicted scenes. The results provide new information for assessing these paintings and are consistent with the known period Monet was in London, suggesting that they contain elements of accurate observation and may potentially be considered as a proxy indicator for the Victorian smogs and atmospheric states they depict. The four dates Monet reports observing the Sun over Parliament in 14 and 16 February and 9 and 24 March 1900, are all represented in the series. The analysis also enables Monet's vantage point from St Thomas' Hospital to be determined for the first time.
On steady rotational high speed flows: the compressible Taylor–Culick profile
Authors: Majdalani Joseph
Published: August 2006

We consider the compressible flow analogue of the well-known Taylor–Culick profile. We first present the compressible Euler equations for steady, axisymmetric, isentropic flow assuming uniform injection of a calorically perfect gas in a porous chamber. We then apply the Rayleigh–Janzen expansion in powers of, whereMwis the wall Mach number. We solve the ensuing equations to the order ofand apply the results up to the sonic point in a nozzleless chamber. Area averaging is also performed to reconcile with one-dimensional theory. Our solution agrees with the existing theory to the extent that it faithfully captures the steepening of the Taylor–Culick profile with downstream movement. Based on the closed-form expressions that we obtain, the main flow attributes are quantified parametrically and compared to the existing incompressible and quasi-one-dimensional theories. Verification by computational fluid dynamics is also undertaken. Comparison with two turbulent flow models shows excellent agreement, particularly in retracing the streamwise evolution of the velocity. Regardless of the Mach number, we observe nearly identical trends in chambers that are rescaled by the (critical) sonic length,Ls. Using a suitable transformation, we prove the attendant similarity and provide universal criteria that can be used to assess the relative importance of gas compression in solid rocket motors. Owing to sharper velocity gradients at the wall, we find that an incompressible model underestimates the skin friction along the wall and underpredicts the centreline speed by as much as 13% at the sonic point. In practice, such deviations become appreciable at high-injection rates or chamber aspect ratios.
The Hide, Skeldon, Acheson dynamo revisited
Authors: Moroz Irene M
Published: August 2006

Hide
et al
. (Hide, Skeldon & Acheson 1996
Proc. R. Soc. A
452
, 1369–1395) introduced a nonlinear system of three coupled ordinary differential equations to model a self-exciting Faraday disk homopolar dynamo. A very small selection of its possible behaviours was presented in that paper. Subsequent studies have extended the system to incorporate the effects of a nonlinear motor, an external battery and magnetic field, the coupling of two or more identical dynamos together, among other things. In this paper, we return to the original model with a view to perform a more extensive analysis of the Hide
et al
. dynamo. For the first time, we present bifurcation transition diagrams, so that the two examples of chaotic dynamo action (shown in
figure 9
in that paper) can now be placed into context. We exhibit the coexistence of multiple attractors and also identify the lowest order unstable periodic orbits pertaining to some specific cases.
Observations on the evolution of wave modulation
Authors: Hwung Hwung-Hweng , Chiang Wen-Son , Hsiao Shih-Chun
Published: August 2006

A series of laboratory experiments on the long-time evolution of nonlinear wave trains in deep water was carried out in a super wave flume (300×5.0×5.2 m) at Tainan Hydraulics Laboratory of National Cheng Kung University. Two typical wave trains, namely uniform wave and imposed sideband wave, were generated by a piston-type wavemaker. Detailed discussions on the evolution of modulated wave trains, such as transient wavefront, fastest growth mode and initial wave steepness effect, are given and the results are compared with existing experimental data and theoretical predictions.

Present results on the evolution of initial uniform wave trains cover a wide range of initial wave steepness (

) and thus, greatly extend earlier studies that are confined only to the larger initial wave steepness region (

). The amplitudes of the fastest growth sidebands exhibit a symmetric exponential growth until the onset of wave breaking. At a further stage, the amplitude of lower sideband becomes larger than the carrier wave and upper sideband after wave breaking, which is known as the frequency downshift.

The investigations on the evolution of initial imposed sideband wave trains for fixed initial wave steepness but different sideband space indicate that the most unstable mode of initial wave train will manifest itself during evolution through a multiple downshift of wave spectrum for the wave train with the smaller sideband space. It reveals that the spectrum energy tends to shift to a lower frequency as the wave train propagates downstream due to the sideband instability.

Experiments on initial imposed sideband wave trains with varied initial wave steepness illustrate that the evolution of the wave train is a periodic modulation and demodulation at post-breaking stages, in which most of the energy of the wave train is transferred cyclically between the carrier wave and two imposed sidebands. Meanwhile, the wave spectra show both temporal and permanent frequency downshift for different initial wave steepness, suggesting that the permanent frequency downshift induced by wave breaking observed by earlier researchers is not permanent. Additionally, the local wave steepness and the ratio of horizontal particle velocity to linear phase velocity at wave breaking in modulated wave group are very different from those of Stokes theory.
Self-harm caused by an insect's innate immunity
Authors: Sadd Ben M , Siva-Jothy Michael T
Published: August 2006

It has been a long-held assumption that the innate immune system of insects causes self-harm when used to combat an immune insult. We show empirically that this assumption is correct. Invertebrate innate immunity relies heavily on effector systems which, on activation, produce cytotoxins that kill pathogens. Reliance on these robust, fast-acting, generic killing mechanisms ensures a potent and rapid response to pathogen invasion, but has the potential disadvantage of causing self-damage. We show that the innate immune response against an immune insult produces measurable phenotypic and functional damage to self-tissue in the beetleTenebrio molitor. This type of self-harm (autoreactivity) and the life-history implications that arise from it are important to understand evolutionary phenomena such as the dynamics between hosts and parasites as well as the nature of immune system costs.
Sibling competition in a brood-tending leech
Authors: Burd Martin , Govedich Fredric R , Bateson Laura
Published: August 2006

Conflict among siblings over parental investment, particularly over parental feeding, is a feature of family life in many kinds of animals. In some bird species, the size of prey items provided to juveniles has been implicated as a cause of aggressive competition among sibling chicks, because prey size determines whether dominance allows monopolization of parental offerings. Our experiment was meant to test the generality of this factor in creating intrafamilial conflict. We investigated sibling competition in relation to prey size using the carnivorous, brood-tending leechHelobdella papillornata. We equalized the total amount of food available toH. papillornatabroods, but varied the size of individual prey items. Competition, measured by disparity in body size at independence, was more intense in broods provisioned with small items than in broods receiving large items, but similar between broods receiving large items and broods fedad libitum. These patterns suggest that the intensity of conflict did not depend only on the total food amount, but was enhanced by small prey size. Our results indicate that conflict over the provision of parental resources to offspring can have a similar basis across very dissimilar organisms.
Evidence that female preferences have shaped male signal evolution in a clade of specialized plant-feeding insects
Authors: Rodríguez Rafael L , Ramaswamy Karthik , Cocroft Reginald B
Published: August 2006

Mate choice is considered an important influence in the evolution of mating signals and other sexual traits, and—since divergence in sexual traits causes reproductive isolation—it can be an agent of population divergence. The importance of mate choice in signal evolution can be evaluated by comparing male signal traits with female preference functions, taking into account the shape and strength of preferences. Specifically, when preferences are closed (favouring intermediate values), there should be a correlation between the preferred values and the trait means, and stronger preferences should be associated with greater preference–signal correspondence and lower signal variability. When preferences are open (favouring extreme values), signal traits are not only expected to be more variable, but should also be shifted towards the preferred values. We tested the role of female preferences in signal evolution in the
Enchenopa binotata
species complex of treehoppers, a clade of plant-feeding insects hypothesized to have speciated in sympatry. We found the expected relationship between signals and preferences, implicating mate choice as an agent of signal evolution. Because differences in sexual communication systems lead to reproductive isolation, the factors that promote divergence in female preferences—and, consequently, in male signals—may have an important role in the process of speciation.
Network frailty and the geometry of herd immunity
Authors: Ferrari Matthew J , Bansal Shweta , Meyers Lauren A , Bjørnstad Ottar N
Published: August 2006

The spread of infectious disease through communities depends fundamentally on the underlying patterns of contacts between individuals. Generally, the more contacts one individual has, the more vulnerable they are to infection during an epidemic. Thus, outbreaks disproportionately impact the most highly connected demographics. Epidemics can then lead, through immunization or removal of individuals, to sparser networks that are more resistant to future transmission of a given disease. Using several classes of contact networks—Poisson, scale-free and small-world—we characterize the structural evolution of a network due to an epidemic in terms offrailty(the degree to which highly connected individuals are more vulnerable to infection) andinterference(the extent to which the epidemic cuts off connectivity among the susceptible population that remains following an epidemic). The evolution of the susceptible network over the course of an epidemic differs among the classes of networks; frailty, relative to interference, accounts for an increasing component of network evolution on networks with greater variance in contacts. The result is that immunization due to prior epidemics can provide greater community protection than random vaccination on networks with heterogeneous contact patterns, while the reverse is true for highly structured populations.
Compliant leg behaviour explains basic dynamics of walking and running
Authors: Geyer Hartmut , Seyfarth Andre , Blickhan Reinhard
Published: August 2006

The basic mechanics of human locomotion are associated with vaulting over stiff legs in walking and rebounding on compliant legs in running. However, while rebounding legs well explain the stance dynamics of running, stiff legs cannot reproduce that of walking. With a simple bipedal spring–mass model, we show that not stiff but compliant legs are essential to obtain the basic walking mechanics; incorporating the double support as an essential part of the walking motion, the model reproduces the characteristic stance dynamics that result in the observed small vertical oscillation of the body and the observed out-of-phase changes in forward kinetic and gravitational potential energies. Exploring the parameter space of this model, we further show that it not only combines the basic dynamics of walking and running in one mechanical system, but also reveals these gaits to be just two out of the many solutions to legged locomotion offered by compliant leg behaviour and accessed by energy or speed.
Pharmacodynamics of non-replicating viruses, bacteriocins and lysins
Authors: Bull James J , Regoes Roland R
Published: August 2006

The pharmacodynamics of antibiotics and many other chemotherapeutic agents is often governed by a ‘multi-hit’ kinetics, which requires the binding of several molecules of the therapeutic agent for the killing of their targets. In contrast, the pharmacodynamics of novel alternative therapeutic agents, such as phages and bacteriocins against bacterial infections or viruses engineered to target tumour cells, is governed by a ‘single-hit’ kinetics according to which the agent will kill once it is bound to its target. In addition to requiring only a single molecule for killing, these agents bind irreversibly to their targets. Here, we explore the pharmacodynamics of such ‘irreversible, single-hit inhibitors’ using mathematical models. We focus on agents that do not replicate, i.e. in the case of phage therapy, we deal only with non-lytic phages and in the case of cancer treatment, we restrict our analysis to replication of incompetent viruses. We study the impact of adsorption on dead cells, heterogeneity in adsorption rates and spatial compartmentalization.
Can the common brain parasite,Toxoplasma gondii, influence human culture?
Authors: Lafferty Kevin D
Published: August 2006

The latent prevalence of a long-lived and common brain parasite,Toxoplasma gondii, explains a statistically significant portion of the variance in aggregate neuroticism among populations, as well as in the ‘neurotic’ cultural dimensions of sex roles and uncertainty avoidance. Spurious or non-causal correlations between aggregate personality and aspects of climate and culture that influenceT. gondiitransmission could also drive these patterns. A link between culture andT. gondiihypothetically results from a behavioural manipulation that the parasite uses to increase its transmission to the next host in the life cycle: a cat. While latent toxoplasmosis is usually benign, the parasite's subtle effect on individual personality appears to alter the aggregate personality at the population level. Drivers of the geographical variation in the prevalence of this parasite include the effects of climate on the persistence of infectious stages in soil, the cultural practices of food preparation and cats as pets. Some variation in culture, therefore, may ultimately be related to how climate affects the distribution ofT. gondii, though the results only explain a fraction of the variation in two of the four cultural dimensions, suggesting that ifT. gondiidoes influence human culture, it is only one among many factors.
Sex-specific foraging strategies and resource partitioning in the southern elephant seal (Mirounga leonina)
Authors: Lewis Rebecca , O'Connell Tamsin C , Lewis Mirtha , Campagna Claudio , Hoelzel A. Rus
Published: August 2006

The evolution of resource specializations is poorly understood, especially in marine systems. The southern elephant seal (Mirounga leonina) is the largest of the phocid seals, sexually dimorphic, and thought to prey predominantly on fish and squid. We collected vibrissae from male and female southern elephant seals, and assessed stable C and N isotope ratios along the length of the vibrissae. Given that whiskers grow slowly, this sampling strategy reflects any variation in feeding behaviour over a period of time. We found that isotopic variation among females was relatively small, and that the apparent prey choice and trophic level of females was different from that for males. Further, males showed a very broad range of trophic/prey choice positions, grouped into several clusters, and this included isotopic values too low to match a broad range of potential fish and cephalopod prey tested. One of these clusters overlapped with data for South American sea lions (Otaria flavescens), which were measured for comparison. Both male southern elephant seals and southern sea lions forage over the continental shelf, providing the potential for competition. We discuss the possibility that individual southern elephant seals are pursuing specialist foraging strategies to avoid competition, both with one another, and with the South American sea lions that breed nearby.
Major cranial changes during
Triceratops
ontogeny
Authors: Horner John R , Goodwin Mark B
Published: August 2006

This is the first cranial ontogenetic assessment of
Triceratops
, the well-known Late Cretaceous dinosaur distinguished by three horns and a massive parietal–squamosal frill. Our analysis is based on a growth series of 10 skulls, ranging from a 38 cm long baby skull to about 2 m long adult skulls. Four growth stages correspond to a suite of ontogenetic characters expressed in the postorbital horns, frill, nasal, epinasal horn and epoccipitals. Postorbital horns are straight stubs in early ontogeny, curve posteriorly in juveniles, straighten in subadults and recurve anteriorly in adults. The posterior margin of the baby frill is deeply scalloped. In early juveniles, the frill margin becomes ornamented by 17–19 delta-shaped epoccipitals. Epoccipitals are dorsoventrally compressed in subadults, strongly compressed and elongated in adults and ultimately merge onto the posterior frill margin in older adults. Ontogenetic trends within and between growth stages include: posterior frill margin transitions from scalloped to wavy and smooth; progressive exclusion of the supraoccipital from the foramen magnum; internal hollowing at the base of the postorbital horns; closure of the midline nasal suture; fusion of the epinasal onto the nasals; and epinasal expansion into a morphologically variable nasal horn. We hypothesize that the changes in horn orientation and epoccipital shape function to allow visual identity of juveniles, and signal their attainment of sexual maturity.
Rapid adaptation of insect herbivores to an invasive plant
Authors: Siemann Evan , Rogers William E , Dewalt Saara J
Published: August 2006

Introduced plant success often is attributed to release from natural enemies in their new ranges. However, herbivores may accumulate over time and reduce invasiveness but evidence for this process to date is weak. We report here that enemy release is indeed limited to the early stages of introduction of the Chinese tallow tree (
Sapium sebiferum
). In bioassays and gardens along a geographical gradient of time since tallow tree introduction, herbivory was highest and tree performance was poorest where tallow tree has been present longer (i.e. introduced earlier). Additionally, Asian ecotypes (grown from seeds collected in Asia) had lower survival than North American ecotypes (seeds collected in North America), which is consistent with genetic responses to low herbivory in the introduced range (EICA Hypothesis). Release from insect herbivores appears to contribute to early success of the tallow tree, but accumulation of insect herbivores has apparently reduced this benefit over time.
Modelling the initial spread of foot-and-mouth disease through animal movements
Authors: Green D.M , Kiss I.Z , Kao R.R
Published: August 2006

Livestock movements in Great Britain (GB) are well recorded and are a unique record of the network of connections among livestock-holding locations. These connections can be critical for disease spread, as in the 2001 epidemic of foot-and-mouth disease (FMD) in the UK. Here, the movement data are used to construct an individual-farm-based model of the initial spread of FMD in GB and determine the susceptibility of the GB livestock industry to future outbreaks under the current legislative requirements. Transmission through movements is modelled, with additional local spread unrelated to the known movements. Simulations show that movements can result in a large nationwide epidemic, but only if cattle are heavily involved, or the epidemic occurs in late summer or early autumn. Inclusion of random local spread can considerably increase epidemic size, but has only a small impact on the spatial extent of the disease. There is a geographical bias in the epidemic size reached, with larger epidemics originating in Scotland and the north of England than elsewhere.
Locating the barnacle settlement pheromone: spatial and ontogenetic expression of the settlement-inducing protein complex ofBalanus amphitrite
Authors: Dreanno Catherine , Kirby Richard R , Clare Anthony S
Published: August 2006

Barnacles are prominent members of hard substratum benthic communities and their study has been important to advances in experimental ecology and contemporary ecological theory. Having recently characterized the cue to gregarious settlement ofBalanus amphitrite, the settlement-inducing protein complex (SIPC), we use two polyclonal antibodies to examine the tissue distribution and ontogenetic expression of this glycoprotein. These antibodies were raised against two separate peptides located near the N- and C-termini of the SIPC and were used to detect the glycoprotein by western blotting and immunohistochemistry. Byin situhybridization we also show that the SIPC mRNA co-occurs with the expressed glycoprotein in the cuticles ofbothnauplius and cypris larval stages and the adult. In the larvae, the SIPC is expressed most strongly in the mouthparts and the hindgut of the stage 2 nauplius and in the thoracopods, antennules and bivalved carapace of the cyprid. In adultB. amphitrite, the expressed SIPC is present in protein extracts of the shell and in all organs that are lined by cuticular tissues. We suggest that the SIPC is produced by the epidermal cells that secrete the cuticle and discuss these observations with regard to earlier studies and the role of the SIPC as a contact pheromone.
Bird navigation: what type of information does the magnetite-based receptor provide?
Authors: Wiltschko Wolfgang , Munro Ursula , Ford Hugh , Wiltschko Roswitha
Published: August 2006

Previous experiments have shown that a short, strong magnetic pulse caused migratory birds to change their headings from their normal migratory direction to an easterly direction in both spring and autumn. In order to analyse the nature of this pulse effect, we subjected migratory Australian silvereyes,Zosterops lateralis, to a magnetic pulse and tested their subsequent response under different magnetic conditions. In the local geomagnetic field, the birds preferred easterly headings as before, and when the horizontal component of the magnetic field was shifted 90° anticlockwise, they altered their headings accordingly northwards. In a field with the vertical component inverted, the birds reversed their headings to westwards, indicating that their directional orientation was controlled by the normal inclination compass. These findings show that although the pulse strongly affects the magnetite particles, it leaves the functional mechanism of the magnetic compass intact. Thus, magnetite-based receptors seem to mediate magnetic ‘map’-information used to determine position, and when affected by a pulse, they provide birds with false positional information that causes them to change their course.
Himalayan porter's specialization: metabolic power, economy, efficiency and skill
Authors: Minetti Alberto E , Formenti Federico , Ardigò Luca P
Published: August 2006

Carrying heavy loads in the Himalayan region is a real challenge. Porters face extreme ranges in terrain condition, path steepness, altitude hypoxia and climate for 6–8 h a day, many months a year, since they were boys. It has been previously shown that, when carrying loads on level terrain, porters' metabolic economy is higher than in Caucasians but the reasons are still unknown. We monitored Nepalese porters both during 90 km trekking in Khumbu Valley and at two different altitudes (3490 and 5050 m above sea-level), where they were compared to Caucasian mountaineers during (22%) gradient walking. Both subject groups carried a load of up to 90% body mass. The remarkably higher performance of porters during uphill locomotion (+60% in speed, +39% mechanical power) is only partly explained by the lower cost of loaded walking (−20%), being also the result of a better cardio-circulatory adaptation to altitude, which generates a higher mass-specific metabolic power (+30%). Consequently, Nepalese porters show higher efficiency, both during uphill and downhill loaded walking. Their higher economy on steep paths cannot be ascribed to a better exchange between potential and kinetic energy, as in our experiments the body centre of mass travelled monotonically uphill (or downhill). A different oscillation pattern of the loaded head–trunk segment, together with the analysis of the different components of the mechanical work during load carrying, suggests that achieved motor skills in balancing the loaded body segment above the hip could play a role in determining the better economy of porters.
Do distantly related parasites rely on the same proximate factors to alter the behaviour of their hosts?
Authors: Ponton F , Lefevre T , Lebarbenchon C , Thomas F , Loxdale H.D , Marché L , Renault L , Perrot-Minnot M.J , Biron D.G
Published: August 2006

Phylogenetically unrelated parasites often increase the chances of their transmission by inducing similar phenotypic changes in their hosts. However, it is not known whether these convergent strategies rely on the same biochemical precursors. In this paper, we explored such aspects by studying two gammarid species (
Gammarus insensibilis
and
Gammarus pulex
; Crustacea: Amphipoda: Gammaridae) serving as intermediate hosts in the life cycle of two distantly related parasites: the trematode,
Microphallus papillorobustus
and the acanthocephalan,
Polymorphus minutus
. Both these parasite species are known to manipulate the behaviour of their amphipod hosts, bringing them towards the water surface, where they are preferentially eaten by aquatic birds (definitive hosts). By studying and comparing the brains of infected
G. insensibilis
and
G. pulex
with proteomics tools, we have elucidated some of the proximate causes involved in the parasite-induced alterations of host behaviour for each system. Protein identifications suggest that altered physiological compartments in hosts can be similar (e.g. immunoneural connexions) or different (e.g. vision process), and hence specific to the host–parasite association considered. Moreover, proteins required to alter the same physiological compartment can be specific or conversely common in both systems, illustrating in the latter case a molecular convergence in the proximate mechanisms of manipulation.
Volatile emission by contest losers revealed by real-time chemical analysis
Authors: Goubault Marlène , Batchelor Tim P , Linforth Robert S.T , Taylor Andrew J , Hardy Ian C.W
Published: August 2006

Animal interactions often involve chemical exchange but simultaneous evaluation of chemistry and behaviour has been problematical. Here we report findings from a novel method, atmospheric pressure chemical ionization-mass spectrometry (APCI-MS) coupled with manipulation of molecular-mass achieved by rearing organisms on deuterium-enhanced nutrients. This allows real-time monitoring of the occurrence and quantity of volatile chemicals released by each of two interacting individuals, in tandem with behavioural observations. We apply these methods to female–female contests in the parasitoid waspGoniozus legneri. We show that this species emits the spiroacetal 2-methyl-1,7-dioxaspiro[5.5]undecane. Chemical release is most common in more behaviourally aggressive contests, which occur when prior resource owners successfully resist take-over by similar-sized intruder females. Volatiles released during contests are always emitted by the loser. Aggression in contests is reduced after spiroacetal release. We suggest that the spiroacetal functions as a weapon of rearguard action. We anticipate that APCI-MS, which is rapid, non-intrusive and relatively inexpensive to operate, will be widely applied in studies linking chemistry and behaviour.
Seasonal plankton dynamics along a cross-shelf gradient
Authors: Stenseth Nils Chr , Llope Marcos , Anadón Ricardo , Ciannelli Lorenzo , Chan Kung-Sik , Hjermann Dag Ø , Bagøien Espen , Ottersen Geir
Published: August 2006

Much interest has recently been devoted to reconstructing the dynamic structure of ecological systems on the basis of time-series data. Using 10 years of monthly data on phyto- and zooplankton abundance from the Bay of Biscay (coastal to shelf-break sites), we demonstrate that the interaction between these two plankton components is approximately linear, whereas the effects of environmental factors (nutrients, temperature, upwelling and photoperiod) on these two plankton population growth rates are nonlinear. With the inclusion of the environmental factors, the main observed seasonal and inter-annual dynamic patterns within the studied plankton assemblage also indicate the prevalence of bottom-up regulatory control.
Plasticity of functional connectivity in the adult spinal cord
Authors: Cai L.L , Courtine G , Fong A.J , Burdick J.W , Roy R.R , Edgerton V.R
Published: August 2006

This paper emphasizes several characteristics of the neural control of locomotion that provide opportunities for developing strategies to maximize the recovery of postural and locomotor functions after a spinal cord injury (SCI). The major points of this paper are: (i) the circuitry that controls standing and stepping is extremely malleable and reflects a continuously varying combination of neurons that are activated when executing stereotypical movements; (ii) the connectivity between neurons is more accurately perceived as a functional rather than as an anatomical phenomenon; (iii) the functional connectivity that controls standing and stepping reflects the physiological state of a given assembly of synapses, where the probability of these synaptic events is not deterministic; (iv) rather, this probability can be modulated by other factors such as pharmacological agents, epidural stimulation and/or motor training; (v) the variability observed in the kinematics of consecutive steps reflects a fundamental feature of the neural control system and (vi) machine-learning theories elucidate the need to accommodate variability in developing strategies designed to enhance motor performance by motor training using robotic devices after an SCI.