Nestmate recognition and the ontogeny of acceptability in the ant,Leptothorax curvispinosus

Summary In social insects, there is often a brief period following eclosion when workers are highly acceptable in alien nests of their own or other species. This study tested for such an acceptance period in the facultatively polygynous ant, Leptothorax curvispinosus, and compared the duration and effectiveness of this period for conspecific and heterospecific introductions. Workers that eclosed and aged for 1–70 h or 30 days in isolation were introduced into either their parental nests (n=24), alien conspecific nests (n=265), or nests of the closely related and biologically similar species, L. longispinosus (n=341). In alien conspecific nests, acceptance was maximal for workers aged 1–12 h at introduction (67.7% not attacked, 75.8% adopted) and gradually decreased until the level of nonaggression (after 60 h) and adoption (after 36 h) were not significantly different from 30-day-old workers (5.9% not attacked, 17.6% adopted). In heterospecific nests, acceptance was maximal for workers aged 1–4 h at introduction (34.8% not attacked, 37.0% adopted) but thereafter was not significantly different from 30-day-old workers (5.6% not attacked, 8.3% adopted). In their parental nests, workers were generally accepted regardless of age (4–56 h posteclosion, 95.8% not attacked, 100% adopted); a result that is consistent with previous research on older workers (38–157 days posteclosion). This study demonstrates an acceptance period that is more effective and of longer duration within than between these species but that, under uniform laboratory conditions, is often not necessary for the integration of workers into their parental colonies. Within colonies, acceptance periods might only be important during relatively brief periods in a colony's life history when eclosing workers produce genetically based nestmate recongition cues that are not already represented in the colony and must be learned by colony members (e.g., during early colony growth or following adoption of queens), or when young workers must acquire environmentally based nestmate recognition cues to achieve and maintain acceptability.     

Comparison of sinking velocity,swimming velocity,rotation and path characteristics among six marine dinoflagellate species

Six marine dinoflagellate species representing a range of equivalent spherical diameters between 12 and 36 m were examined for several characteristics that influence their translation velocity. Sinking velocities estimated by three independent techniques and applied to swimming and narcotized cells generally agreed, and followed the cell-size relationships previously reported for diatoms. Dinokont sinking and swimming velocities both decreased with increasing surface area: volume ratio, but a small desmokont deviated from the dinokont relationships. Sinking velocities influenced the relative ascent/descent capabilities of a species. The swim:sink ratio decreased as equivalent spherical diameter increased to 25 m and then remained constant at 7.6, despite further increases in cell size. This relationship suggests a minimum required swimming capability relative to cell size. The swim:sink ratio increased with increasing surface area:volume ratio for all the surveyed species. Out observations of decreasing cell rotation:translation ratio and increasing cell drag with increasing cell size supported the hypothesis that the dinoflagellate flagellar apparatus generates maximum swimming velocity at intermediate cell sizes. However, an alternate analysis supported the hypothesis that swimming velocity increases with cell size and that variations among genera are due to subtle differences in the basic dinoflagellate propulsion system. A three-dimensional helical path index provided a more realistic estimate of the actual translation velocity (along the helix axis) during diel vertical migration when applied as a correction factor to the more typically measured helix velocity (along the helix) of a given dinoflagellate.     

The challenge of sustainable tourism

The paradigm of sustainable tourism is discussed in terms of analysing what it actually means. Certain questions are raised and these include the means of its measurement, the question of intergenerational impacts and how these may be assessed, the determination of what exactly is meant by environment, the aspect of tourism as an industry and, with specific reference to tourism in the developing world, the potential for neocolonialism. It is argued that, although sustainable tourism may be a worthwhile goal, inherent problems in the definition and measurement of its success make it an elusive if not academic target. The challenge of sustainable tourism is to see it in a broader context as but one tool of development and to ensure that it is examined in the context of the local community as well as a global perspective.     

Normal fetal cardiac anatomy–a basis for the echocardiographic detection of abnormalities

Real-time examination of the fetal heart in 350 pregnancies has allowed a composite picture of normal fetal cardiac anatomy to be established and echocardiographic interpretation has been confirmed by anatomical studies. Two echocardiographic sections are readily obtainable and are suggested as applicable to routine scanning but the specialist nature of interpreting abnormalities is stressed. Six abnormalities have been suspected during the study and five confirmed anatomically or at cardiac catheterization. In view of the low incidence of congenital heart disease in a normal obstetric population, high risk groups should perhaps be selected for cardiac scanning at the present time. These include mothers of previously affected babies, diabetic mothers and certain abnormalities of pregnancy. Fetal ascites is particularly important, being present in three of the four proven cases of cardiac abnormality.     

A chemical view of the most ancient metazoa--biomarker chemotaxonomy of hexactinellid sponges

Hexactinellid sponges are often considered to be the most ancient metazoans. Lipid biomarkers from 23 species were studied for information on their phylogenetic properties, particularly their disputed relation to the two other sponge classes (Demospongiae, Calcarea). The most prominent lipid compounds in the Hexactinellida comprise C28 to C32 polyenoic fatty acids. Their structures parallel the unique patterns found in demosponge membrane fatty acids ('demospongic acids') and strongly support a close phylogenetic association of the Demospongiae and the Hexactinellida. Both taxa also show unusual mid-chain methylated fatty acids (C15-C25) and irregular C25- and C40-isoprenoid hydrocarbons, tracers for specific eubacteria and Archaea, respectively. These biomarkers indicate a similar, highly conservative symbiont community, although some shift in the abundance of the associated microbiota was observed. The lack of these features in calcareous sponges further contradicts the still common view that Calcarea and Demospongiae are more closely related to each other than either is to the Hexactinellida.     

Early sonographic diagnosis of body stalk anomaly

Ultrasonographic features of a fetus at 18 weeks of gestation suggesting a body stalk anomaly are presented. These included a large abdominal anterior wall defect in apparent continuity with the placenta, severe kyphoscoliosis of the lower spine, the absence of one kidney, and a very short umbilical cord with only one umbilical artery. The amniotic fluid was reduced and the fetus was almost immobile at short-interval ultrasound examinations. The pregnancy was terminated and autopsy of the fetus showed abnormalities compatible with maldevelopment of both cephalic and caudal embryonic folds.     

Measurement of the fetal mandible—feasibility and construction of a centile chart

The prenatal diagnosis of micrognathia is usually based on a subjective impression of the size of the jaw when examining the fetal profile. We have constructed a centile chart for mandibular length between 12 and 27 post-menstrual weeks in a cross-sectional study of 184 fetuses. The application of this chart in clinical practice may permit a more objective diagnosis of micrognathia in the prenatal period.     

Prenatal ultrasonographic diagnosis of radial-ray reduction malformations

Radial-ray reduction malformations (RRRMs) may occur isolated or in association with other anomalies. The data of seven fetuses born with RRRMs were collected. Six fetuses had associated lethal abnormalities of the central nervous system, urogenital system, and/or heart, detected by ultrasound. In five cases, it was possible to establish the precise diagnosis, enabling an informed prognosis and subsequent genetic counselling. The diagnoses were: Edwards syndrome (n=3), VACTERL association (n=1), and Poland-Moebius-like complex (n= 1). In two cases, a complete diagnosis was not possible because of inadequate evaluation of these fetuses before and/or after birth. A proposal is given for the diagnostic approach for infants with RRRMs detected in the antenatal period by means of ultrasonography.     

Economic aspects of appropriative water rights

In the and portion of the western U.S., economic development has been affected by the doctrine of appropriative water rights. This paper considers the efficiency aspects of the appropriative doctrine for the case of a stochastic and uncontrolled river, then, subsequently, extends the analysis to the case where the presence of an upstream storage facility provides some degree of flexibility in determining releases. Lastly, the effects of institutions which limit the degree of river use and the implicit release policies attendant are considered.     

Emissions Trading with Shares and Coupons when Control over Discharges Is Uncertain

Two important decisions in designing markets for tradable emissions permits are whether to allow banking of permits (coupons) and whether to allow trading in entitlements to future permits (shares). Banking is predicted to reduce price instability when firms trade in a reconciliation market after the quantity of emissions has been determined. Tradable shares are a common feature in proposals for emissions trading in Canada. We conduct a laboratory experiment to investigate how bankable coupons and tradable shares affect efficiency and prices under uncertainty. Cognitive demands on the subjects are reduced by computerized advice on the optimal allocation of coupons across periods and the implied marginal values of coupons and shares. Banking, share trading, and uncertainty conditions are introduced in a complete factorial design with three observations per cell. High efficiencies are observed across all treatments. Uncertainty in the control of emissions leads to substantial price instability when banking is not allowed. Banking virtually eliminates the instability, but reduces the efficiency of the market institution. Share trading reduces trading volumes, increases price stability, and improves efficiency.