Loads on an internal spinal fixation device during sitting.

Sitting is often assumed to involve high loads on the spine as well as on implants for stabilising the spine. Loads on internal spinal fixation devices were therefore measured in ten patients sitting on several types of seats, including a stool, a stool with a padded wedge, a chair, a physiotherapy ball, a knee-stool, and a bench. The patients also successively sat relaxed and erect on a stool. In addition, six of them sat on a special chair allowing different inclinations of the backrest. Implant loads were also measured for standing up and sitting down. There were only minor differences in fixator loads for sitting on the different types of seats. Sitting erect caused an average of 11% higher implant loads than sitting relaxed. Implant loads decreased with increasing inclination of the upper body while sitting on a chair with an adjustable backrest. Implant loads were about 27% higher for standing up and sitting down than for sitting.     

Cellular injury and carcinogenesis. The effect of a protein-free high-carbohydrate diet on the metabolism of dimethylnitrosamine in the rat

1. Rats fed on a protein-free high-carbohydrate diet for 7 days metabolized dimethylnitrosamine at only 55% the rate of rats fed on a commercial diet. 2. Dimethylnitrosamine was metabolized by liver slices from rats fed on the protein-free diet at less than half the rate attained by slices from rats fed on a commercial diet. But kidney slices from these rats metabolized dimethylnitrosamine at the same rate as kidney slices from rats on a commercial diet. 3. Methylation by dimethylnitrosamine (70mg/kg body wt.) of N-7 of guanine of the liver RNA and DNA of rats fed on a protein-free diet was only slightly higher than in rats fed on a normal diet given 27mg/kg body wt. In contrast, the methylation by dimethylnitrosamine of guanine in kidney nucleic acids of these rats was three times that in the rats fed on a normal diet. 4. In rats fed on a protein-free diet the incidence of kidney tumours produced by a single dose of dimethylnitrosamine is increased.     

Metapopulations of moths on islands: a test of two contrasting models

1. We describe a generalized mainland-island metapopulation model which includes migration among the island populations. We test model predictions with quantitative data on more than 200 species of moths in two contrasting networks of small islands. The data include a direct measure of migration rate, based on trapping of moths on rocky skerries with no local populations of the vast majority of species.
2. We predicted that moths which are strong fliers but uncommon on the islands have a higher incidence on scattered islands than on islands in a group, because the latter 'compete' for immigrants from the mainland. In contrast, we predicted that weakly flying species with potentially large local populations on the islands occur more frequently on islands in a group due to enhanced colonization rate.
3. Both predicted patterns were observed. Island occupancy increased significantly with the number of individuals caught on the rocky skerries, which is our measure of migration rate from the mainland, supporting the basic assumption that the species occur on the islands in a balance between colonizations and extinctions.
4. These results demonstrate that the moth metapopulations on islands represent a mixture of Levins's and mainland-island metapopulations, and that the mixture is different for different species in the same landscape.     

Investigating species incidence over habitat fragments of different areas—a look at error estimation

The use of incidence functions and their error structure is explored as a means of interpreting patterns present in fragmented systems. Incidence functions describe the probability of a species' presence on a fragment. The only information required for an incidence function is presence/absence data for a number of fragments of known size. Methods are developed for establishing prediction bounds on the incidence function. The example developed uses data from mammals on isolated mountaintops. Distributions of number of species expected on a fragment predicted the actual number of species well, but prediction of identities of species on small fragments was poor. Although the number of species expected on an assembly of small fragments compared to a single large fragment of the same total area was nearly always equal, the identity of species differed. Species with large area requirements were never found on any number of small fragments; species which occurred with a medium probability over most fragments had a higher probability of being present in an assembly of small fragments than on a single large fragment.     

Inter-joint coordination of posture on a seesaw device

Even though specific adjustments of the multi-joint control of posture have been observed when posture is challenged, multi-joint coordination on a seesaw device has never been accurately assessed. The current study was conducted in order to investigate the multi-joint coordination when subjects were standing on either a seesaw device or on a stable surface, with the eyes open or closed. Eighteen healthy active subjects were recruited. A principal component analysis and a Self-Organizing Maps analysis were performed on the joint angles in order to detect and characterize dominant coordination patterns. Intermuscular EMG coherence was analysed in order to assess the neurophysiological mechanisms associated with these coordination patterns. The results illustrated a multi-joint organization of posture on both stable ground and on the seesaw, with a higher variability among the individual postural responses observed when standing on the seesaw. These findings challenge the classical assumption of ankle mechanisms as dominating control on seesaw devices and confirm that inter-joint coordination in postural control is strongly modulated by stance conditions. When standing on the seesaw without vision, a decrease in intermuscular coherence was observed without any impact on the joint coordination patterns, likely due to an increase dependence on proprioceptive information.     

Decision between small and large prey: reduced energy acquisition by pre-migratory purple sandpipers,Calidris maritima,on Svalbard

On Svalbard, purple sandpipers forage on the shores when preparing for autumn migration to the European continent after a period of food shortage on the tundra in summer. Their food choice was studied on a beach when they were faced with the choice between two abundant prey species: a small collembolan (springtail) and a much larger amphipod. In spite of several times higher gain of energy when foraging on amphipops, the birds did not show a distinct preference for either of the two prey species in this situation. Alternative explanations for this behaviour are discussed. We suggest that this could be a consequence of adaptations to their summer diet on Svalbard, when they rely on Collembola as food to a considerable extent. Higher variance in energy gain rate when foraging on amphipods might also be important. Collembolan densities high enough to trigger predation from birds occurred only on some days, with cloudy calm weather. This, together with the possible existence of a dietary bottleneck, may reduce the cost associated with the switch to Collembola. Accepted: 25 April 1999     

Plant cues influence searching behaviour and parasitism in the egg parasitoid Trichogramma nr. brassicae

Abstract. 1. The effect of experience of plant cues at emergence on searching behaviour and parasitism was investigated in two strains of Trichogramma nr. brassicae (Hymenoptera: Trichogrammatidae).
2. Wasps reared on Sitotroga cereallela were allowed to emerge on a tomato plant or in a vial, with or without food. For one of the strains, females emerging on tomato searched significantly longer on a tomato seedling than females emerging in a vial.
3. The experience effect lasted between 1 and 2 days. It involves associating plant stimuli with the remains of the host, because females emerging from their host on a tomato plant had an increased searching response to tomato, but females transferred to the plant immediately after emergence did not.
4. The effect of emergence environment on parasitism of the host Helicoverpa punctigera on tomato and lettuce seedlings was tested. Wasps were allowed to emerge on seedlings of tomato or lettuce, or in an empty vial. For one strain, females experienced with tomato at emergence parasitized significantly more hosts on tomato than did females emerging on lettuce or in a vial. Parasitism on lettuce was not influenced by the treatments.     

The inheritance of fingerprint patterns.

Analysis of the fingerprints of 571 members of the Habbanite isolate suggest inherited patterns and pattern sequences. A genetic theory has been developed; it assumes that the basic fingerprint pattern sequence is all ulnar loops and that a variety of genes cause deviations from this pattern sequence. Genes that have been proposed include: (1) a semidominant gene for whorls on the thumbs (one homozygote has whorls on both thumbs, the other has ulnar loops on both thumbs and the heterozygote usually has two ulnar loops or one ulnar loop and one whorl); (2) a semidominant gene for whorls on the ring fingers which acts like the gene for whorls on the thumbs; (3) a dominant gene for arches on the thumbs and often on other fingers; (4) one or more dominant genes for arches on the fingers; (5) a dominant gene for whorls on all fingers except for an ulnar loop on the middle finger; (6) a dominant gene for radial loops on the index fingers, frequently associated with an arch on the middle fingers; and (7) a recessive gene for radial loops on the ring and little fingers. These genes may act independently or may show epistasis.     

Emergence of donor control in patchy predator—prey systems

We study a general predator—prey system in a spatially heterogeneous environment. The predation process, which occurs on a behavioural time-scale, is much faster than the other processes (reproduction, natural mortality and migrations) occurring on the population dynamics time-scale. We show that, taking account of this difference in time-scales, and assuming that the prey have a refuge, the dynamics of the system on a slow time-scale become donor-controlled. Even though predators may control the prey density locally and on a behavioural fast time-scale, nevertheless, both globally and on a slow time-scale, the prey dynamics are independent of predator density: the presence of predators generates a constant prey mortality. In other words, in heterogeneous environments, the prey population dynamics depend in a switch-like manner on the presence or absence of predators, not on their actual density.     

Trichogramma egg parasitism ofHelicoverpa armigera on short-duration pigeonpea intercultured with sorghum

The levels of egg parasitism byTrichogramma spp. (Hymenoptera: Trichogrammatidae) on populations ofHelicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) were recorded on sorghum (Sorghum bicolor L.) and on two flushes of flowers on short-duration pigeonpea (Cajanus cajan L.).H. armigera oviposition was concentrated on the early flowering stage of sorghum and the flowering and early podding stages of both flushes of pigeonpea. Parasitism on sorghum increased rapidly as egg density increased and reached a peak of 74.6%. Parasitism on pigeonpea was concentrated onH. armigera eggs laid on the first flush of pigeonpea flowers with a maximum of 69.2%. These high levels of parasitism on pigeonpea coincided with the period of parasite activity on sorghum. The levels of parasitism then declined rapidly and only very low levels were detected on a second flush of flowers. This rapid decline resulted in the overall egg mortality caused byTrichogramma on pigeonpea to be low, with a maximum of 7.8% caused by parasitism, compared to 34.4% on sorghum. The pattern of parasitism suggests that a transfer of parasites occurred from sorghum to pigeonpea. The rapid decline of parasitism on the pigeonpea indicates that parasite populations cannot be sustained on pigeonpea once the influx from sorghum stops. The results are discussed in terms of a possible method of encouraging the transfer of parasites from sorghum to short-duration pigeonpea by producing a more continuous cropping environment.     

Cladistic information in phylogenetic definitions and designated phylogenetic contexts for the use of taxon names

A phylogenetic definition of a taxon name associates that name with a clade through its reference to a particular ancestor and all of its descendants. Depending on one's perspective, phylogenetic definitions name either clades on the one true, but unknown, phylogeny, or components on cladograms (clades on hypotheses regarding the true phylogeny). Phylogenetic definitions do not contain enough information to identify components without a reference cladogram. As a result, (1) if clades are equated with components on cladograms, a phylogenetic definition may associate a taxon name with different clades on different cladograms, and (2) the inclusiveness, diagnostic synapomorphies, and distribution in time and space of the clade with a particular name can differ markedly depending on the phylogenetic hypothesis one chooses to adopt. This potentially unacceptable lability in the clade to which a name refers can be avoided by using a taxon name in conjunction with only phylogenetic hypotheses on which specific taxa are related in a particular fashion. This designated phylogenetic context can be described in an n-taxon statement that would be appended to the phylogenetic definition. Use of the taxon name would be considered inappropriate in conjunction with cladograms on which the relationships contradict those in the n-taxon statement. Whereas phylogenetic definitions stabilize the meaning of taxon names, designated phylogenetic contexts would stabilize the usage of those names.     

Avirulent isolates of Corynebacterium fascians that are unable to utilize agmatine and proline.

Growth of a highly virulent strain of the phytopathogen Corynebacterium fascians on rich media at 37 degrees C resulted in a loss of virulence in a majority of the population within 10 generations. Strains retained virulence during cultivation at 30 degrees C on a minimal medium with ammonia as a nitrogen source. Populations of avirulent strains on the surfaces of pea seedlings decreased, whereas the number of cells of the virulent strain increased 1,000-fold during a 3-week period. All avirulent mutants isolated by growth on rich media at 37 degrees C were unable to grow on media containing agmatine or proline as sole sources of nitrogen. The ability of the mutants to grow on pea seedlings and cause fasciation disease appeared to be related to their ability to utilize nitrogen sources available on plant surfaces.     

Related Causal Frameworks for Surrogate Outcomes

Summary .  Four major frameworks have been developed for evaluating surrogate markers in randomized trials: one based on conditional independence of observable variables, another based on direct and indirect effects, a third based on a meta-analysis, and a fourth based on principal stratification. The first two of these fit into a paradigm we call the causal-effects (CE) paradigm, in which, for a good surrogate, the effect of treatment on the surrogate, combined with the effect of the surrogate on the clinical outcome, allow prediction of the effect of the treatment on the clinical outcome. The last two approaches fall into the causal-association (CA) paradigm, in which the effect of the treatment on the surrogate is associated with its effect on the clinical outcome. We consider the CE paradigm first, and consider identifying assumptions and some simple estimation procedures; we then consider the CA paradigm. We examine the relationships among these approaches and associated estimators. We perform a small simulation study to illustrate properties of the various estimators under different scenarios, and conclude with a discussion of the applicability of both paradigms.     

Struttura e periodismo dei popolamenti a Cystoseira(Fucophyceae,Fucales) del Mediterraneo

Abstract

News on both the structure and the periodism of the communities with Cystoseira from the Mediterranean Sea based on literature data, are presented.

In order to a better knowledge of such communities, the opportunity of a standardized methodology based on a preliminary study of the qualitative minimal area, on monthly samples to be carried out throughout a year as well as on observations on the vertical distribution of species within the community, is suggested.     

Differential inhibition of branching enzyme in a morphological mutant and in wild type Neurospora. Influence of carbon source in the growth medium.

1. A morphological mutant of Neurospora crassa, smco 9, (R2508) that exhibits colonial morphology when grown on sucrose or on maltose, showed a partial reversal of this morphology toward that of the wild type when it was grown on potato starch or on isomaltose. 2. A common feature of both potato starch and isomaltose is the presence of alpha-1, 6 glucosidic linkages. This suggested that these morphological effects might be due to differences in alpha-1,4 glucan: alpha-1,4 glucan 6 glycosyltransferase, (EC 2.4.1.18) commonly known as "the branching enzyme". 3. The branching enzyme was purified from wild type, Neurospora crassa, and from the semicolonial mutant, R2508, both grown on sucrose or on potato starch. It has a molecular weight of 140,000 as estimated by gel filtration on a Bio Gel A 1.5 m column. This enzyme plus phosphorylase a in an unprimed reaction catalyzes the synthesis of a branched polysaccharide in vitro. 4. No branching enzyme activity was apparent in extracts of the mutant R2508, grown on potato starch until a thermolabile inhibitor was removed by fractionation on a DEAE column. 5. This inhibitor has a molecular weight greater than 100,000 as estimated on a P-100 polyacrylamide gel column. The specificity of the inhibitor is not absolute in that it inhibits glycogen synthetase in addition to the branching enzyme in Neurospora.     

Fig Wasps: A Staple Food for Ants on Ficus

Mutualisms involve the exchange of resources and these resources attract exploiters and predators. Because predators may have a stronger effect either on mutualists or on exploiters, their net effect on the mutualism may be positive or negative. Ants and Ficus -associated wasps are a potential example. These wasps could represent sufficient food to ensure a permanent presence of predators. If this is the case then we may expect divergent selection (dependent on fig species) on traits facilitating or impeding ant predatory activity. Dioecious Ficus species in Brunei present the opportunity to determine whether presence of fig wasps on a tree ensures increased presence of ants because: (1) wasps are mainly present on male trees, thus allowing study of the effect of wasp abundance on ant presence; and (2) preliminary observations showed that ants present on trees were mainly predatory species that do not tend hemipterans. We show here, for several dioecious Ficus species, that many more ants were present on male trees than on female trees. Furthermore, these ants were mainly dominant predatory taxa that often nested in the male trees. Hence, wasps on male trees provide a sufficient resource in terms of quantity and reliability to ensure the continuous presence of dominant ants on the trees.     

Effect of an additional manual motor task on the maintenance of equilibrium in the frontal and sagittal planes in standing subjects

The postural oscillations of a standing subject during an additional manual motor task consisting in holding a movable ball in the center of a flat box were studied. The movements of the center of pressure (CP) in the frontal and sagittal planes were studied when subjects were standing on a stable rigid support and on a movable unstable support. The effect of the additional motor task on the movement of the CP depended on the stability of the support. When the additional task was performed, the sagittal movements of the CP increased in the case a movable support and did not increase when the support was stable. The additional task decreased the frontal movements of CP in the case of a stable support, and it did not change the frontal movements of CP when the support was unstable. Thus, the performance of an additional motor task led to a reduction of the efficiency of the postural control system in maintaining equilibrium on an unstable support. This decrease may be due to a greater cortical influence on the posture control system in subjects standing on a movable support in comparison with this influence in the case of a stable support.     

Multiple DNA and protein sequence alignment on a workstation and a supercomputer

This paper describes a multiple alignment method using a workstationand supercomputer. The method is based on the alignment of aset of aligned sequences with the new sequence, and uses a recursiveprocedure of such alignment. The alignment is executed in areasonable computation time on diverse levels from a workstationto a supercomputer, from the viewpoint of alignment resultsand computational speed by parallel processing. The applicationof the algorithm is illustrated by several examples of multiplealignment of 12 amino acid and DNA sequences of HIV (human immunodeficiencyvirus) env genes. Colour graphic programs on a workstation andparallel processing on a supercomputer are discussed. Received on April 26, 1988; accepted on July 7, 1988