Glucose-6-phosphate Dehydrogenase Activity under Conditions of Water Limitation: a Possible Model System for Enzyme Reactions in Unimbibed Resting Seeds and its Relevance to Seed Viability

A model system has been used to measure glucose-6-phosphatedehydrogenase (G-6-PDH) activity when the water contents ofthe reactants are comparable to the water contents of dry restingseeds. The activity of G-6-PDH is reduced by 10²–10³ whenthe water content is limited to between 1.5 and 25 per cent.G-6-PDH activity is affected by temperature and by the proteincontent of the model system. The glucose 6-phosphate (7.03 nmolg^–1 embryo) and the NADP⁺ (25.0 nmol g^–1 embryo)contents of barley embryos were measured. Using these measurements,together with the measurements in the model system of G-6-PDHactivity at low water concentrations, an estimate is made ofthe G-6-PDH activity in resting barley embryo. A cor-relationbetween estimated G-6-PDH activity at different water contentsand the periods for which seeds remain viable is indicated.The limitations of the model system are discussed.     

Seasonal Changes in the Physiology of S24 Perennial Ryegrass (Lolium perenne L.). 2. Potential Leaf and Canopy Photosynthesis during the Transition from Vegetative to Reproductive growth

The photosynthetic potential of successive youngest fully-expandedleaves of S24 L. perenne, grown as simulated swards under naturalenvironmental conditions, was measured during establishmentin autumn, over winter and during the transition from vegetativeto reproductive growth the following spring. Measurements weremade at a standard light energy receipt of 250 J m^–2 s^–1(400–700 nm) and at 15 °C. The photosynthetic potential of the leaves decreased in autumnas the swards increased in density under worsening environmentalconditions. During the spring, photosynthetic rates rose fromlow over-winter values so that by March, before stem elongationbegan, they were equal to the rates in the previous autumn.Following stem elongation there was a further increase in leafpotential. Reasons for these changes in leaf potential are discussed. During spring, the photosynthetic potential of the canopy alsorose - both as measured, and as predicted by the Monteith modelof canopy photosynthesis. Use of the model suggested that increasingleaf potential made the greatest contribution to the rise inthe potential of the canopy, although, following stem elongation,changes in LAI and canopy structure had a further significanteffect.     

Respiratory Efflux of Carbon Dioxide from Mature and Meristematic Tissue of Uniculm Barley During Eighty Hours of Continuous Darkness

Young plants of uniculm barley were grown singly in pots ina growth room at 23/21 °C, and an irradiance of 655 µEm^–2s^–1 during each 12 h photoperiod. At the fifth leaf stage,they were subjected to 80 h of continuous darkness during whichthe rates of CO₂ efflux of vegetative shoot meristems, and maturefully expanded leaves, were separately monitored. Respiratoryefflux from the meristematic tissue was initially high, 12–15mg CO₂ g^–1 h^–1, equivalent to a daily loss in weightof 20–25 per cent. It remained high, or even rose slightly,during what would have been the normal dark period, but thenfell sharply. Even so, it was still three times that of themature tissue at the end of the experimental period. The rateof CO₂ efflux of the mature tissue began low, and fell evenfurther during the first 12 h of darkness. It then levelledoff at a rate of 2·0–2·5 mg CO2 g^–1h^–1, equivalent to a daily loss in weight of about 3 percent. It is suggested that the rate of ‘mature tissue’respiration, established after 12–24 h of darkness, mightbe a useful selection criterion to employ in attempts to increasethe total dry matter yield of the grass crop by breeding. Hordeum vulgare L., barley, respiration, synthetic respiration, maintenance respiration, meristem, mature tissue respiration, simulated sward     

Scanning electron microscope study of the palar pegs of three species of Corixidae (Hemiptera)

Scanning electron microscope studies were performed on the palar pegs of male forelegs of Trichocorixa sexcincta, Sigara alternata and Hesperocorixa interrupta. The studies showed the pegs to be basically conical and chevron-ridged, with a wide base that tapered of to a narrow apex. Clear species differences were apparent with respect to the size of the peg, the number of ridges on an individual peg, and the number and arrangement of the pegs on the pala. The possible behavioural and evolutionary significance of the palar pegs is discussed in relation to mating.     

Relative roles of dispersal dynamics and competition in determining the isotopic niche breadth of a wetland fish

1. The niche variation hypothesis predicts that among‐individual variation in niche use will increase in the presence of intraspecific competition and decrease in the presence of interspecific competition. We sought to determine whether the local isotopic niche breadth of fish inhabiting a wetland was best explained by competition for resources and the niche variation hypothesis, by dispersal of individuals from locations with different prey resources or by a combination of the two. We analysed stable isotopes of carbon and nitrogen as indices of feeding niche and compared metrics of within‐site spread to characterise site‐level isotopic niche breadth. We then evaluated the explanatory power of competing models of the direct and indirect effects of several environmental variables spanning gradients of disturbance, competition strength and food availability on among‐individual variation of the eastern mosquitofish (Gambusia holbrooki). 2. The Dispersal model posits that only the direct effect of disturbance (i.e. changes in water level known to induce fish movement) influences among‐individual variation in isotopic niche. The Partitioning model allows for only direct effects of local food availability on among‐individual variation. The Combined model allows for both hypotheses by including the direct effects of disturbance and food availability. 3. A linear regression of the Combined model described more variance than models limited to the variables of either the Dispersal or Partitioning models. Of the independent variables considered, the food availability variable (per cent edible periphyton) explained the most variation in isotopic niche breadth, followed closely by the disturbance variable (days since last drying event). 4. Structural equation modelling provided further evidence that the Combined model was best supported by the data, with the Partitioning and the Dispersal models only modestly less informative. Again, the per cent edible periphyton was the variable with the largest direct effect on niche variability, with other food availability variables and the disturbance variable only slightly less important. Indirect effects of heterospecific and conspecific competitor densities were also important, through their effects on prey density. 5. Our results support the Combined hypotheses, although partitioning mechanisms appear to explain the most diet variation among individuals in the eastern mosquitofish. The results also support some predictions of the niche variation hypothesis, although both conspecific and interspecific competition appeared to increase isotopic niche breadth in contrast to predictions that interspecific competition would decrease it. We think this resulted from high diet overlap of co‐occurring species, most of which consume similar macroinvertebrates.     

Lycophytes from the Middle Triassic (Anisian) locality Kühwiesenkopf (Monte Prà della Vacca) in the Dolomites (northern Italy)

Abstract: Generally, lycophytes are not well represented in Anisian floras. Nonetheless, four different genera, each with one species, have been distinguished in the Anisian flora from Kühwiesenkopf (Monte Prà della Vacca), Italy. They were well preserved and yielded leaf cuticles in all four taxa and in situ spores in two of them. Lycopia dezanchei gen. et sp. nov. is the most common form; it is characterized by a dichotomising creeping prostrate rhizome (representing the primary shoot axis) from which arise aerial axes, apically bifurcated and covered with bundles of long leaves. This taxon cannot be attributed to any of the lycophyte orders, but most resembles Lycopodiales. Two representatives of the Isoetales have been found, of which Isoetites brandneri sp. nov. is abundant. This species is characterized by a short stem, which is unusual for this genus. In situ immature microspores and megaspores were found in some specimens. Lepacyclotes bechstaedtii sp. nov. has a quadrilobe corm with fertile scales inserted in whorls or slightly helicoidally. Short sterile leaves arise distally from the corm in some specimens. Selaginellales are very rare in the flora; Selaginellites leonardii sp. nov. is represented by a strobilus that yielded both micro‐ and megaspores. Some sterile fragments have been found associated, but never in organic connection.     

Description of a new species of Phylloscopus warbler from Vietnam and Laos

A new species of Phylloscopus warbler, which we name Phylloscopus calciatilis Limestone Leaf Warbler, is described from central and northern Vietnam and central and northern Laos; it probably also breeds in southernmost China. In morphology, the new species is very similar to Sulphur-breasted Warbler Phylloscopus ricketti , but it is smaller with a proportionately larger bill and rounder wing. Its song and calls are diagnostic. Based on mitochondrial and nuclear DNA, the new species is most closely related to P. ricketti and Yellow-vented Warbler Phylloscopus cantator , and it is inferred to be sister to the latter. The mitochondrial divergences between these three species are at the low end of the variation found in other species of Phylloscopus and Seicercus warblers, but greater than in other taxa generally treated as subspecies. Possible introgressive hybridization between the new species and P. ricketti is discussed, but more data are needed to establish whether it does occur and, if it does, to what extent. The new species appears to have a restricted breeding range in limestone karst environments, where it is locally common and therefore not under any immediate threat. In view of the recognition of the new species, all previous records of P. ricketti sensu lato need to be re-evaluated.     

Using Resource Selection Functions to Improve Estimation of Elk Population Numbers

Abstract: Stratification is commonly used to improve sampling efficiency of aerial surveys of ungulate populations with strata typically based on a priori information, such as preflight animal observations or vegetation attributes as surrogates for animal densities. We evaluated the usefulness of stratifying survey units for elk (Cervus elaphus) in the Rocky Mountain foothills of Alberta, Canada, using a resource selection function (RSF). We compared precision and design efficiency (DEFF) of population estimates from stratification approaches based on an RSF model to the past approach using amount of forest cover. We used a sample of telemetry relocations taken over a 3-year period from 165 elk, rarified to times of the day and months of the year when aerial surveys are conducted, to develop the RSF. We then used the top RSF model, based on Akaike's Information Criterion, to derive the average RSF value for an 8-km² survey unit. Using survey data from the first year, we evaluated binning schemes to define RSF-oriented strata based on poststratification and showed that Jenks natural breaks in the RSF values provided the greatest improvement in DEFF and increased precision, compared to 2 other stratification schemes. We then used this approach with data from 2 additional surveys to find that stratification by RSF consistently improves relative precision and design efficiency of elk population estimates, whether we employ pre- or poststratification. Where a RSF is available it could be used as a surrogate for animal densities when conducting stratified sampling for population surveys.     

A BACTERIAL METHOD FOR TRACING SEWAGE POLLUTION

SUMMARY: Serratia indica , added to raw sewage, has been used to discover the distribution of effluent material discharged into the sea. Results were obtained after six days, but a new variant of Sr. indica has been selected which should give identifiable colonies in 48 hr.