AN EARLY CENOZOIC NEOSELACHIAN SHARK FAUNA FROM THE SOUTHWEST PACIFIC

Abstract: An early Cenozoic shark fauna, comprising at least 16 taxa, is described from Paleocene sedimentary rocks on the South Island of New Zealand. Although representing a remote Southern Hemisphere location, the fauna includes forms closely comparable to contemporary species from the Northern Hemisphere, in addition to the new species Chlamydoselachus keyesi and Centroselachus goordi. Comparison with closely related extant species suggests the fauna may be interpreted as a deep water one, typical of the outer continental shelf and upper slope. However, after palaeogeography, sedimentology and mineralogy of the enclosing rock, and the nature of similar faunas from elsewhere are taken into consideration, the fauna is interpreted to have occupied a mid‐shelf environment.     

Habitat use by the inland carpet python (Morelia spilota metcalfei: Pythonidae): Seasonal relationships with habitat structure and prey distribution in a rural landscape

Abstract Squamate reptiles are significant components of woodland vertebrate communities in eastern Australia, but their ecology is poorly understood. We investigated seasonal variation in habitat use by the Inland Carpet Python, Morelia spilota metcalfei Wells and Wellington (Pythonidae), a threatened snake that inhabits the woodland environments of the Murray–Darling Basin. Nine pythons were radiotracked within and near the Mount Meg Flora and Fauna Reserve in north‐eastern Victoria to investigate how habitat structure and prey distribution (namely, that of the European Rabbit, Oryctolagus cuniculus L. (Leporidae)) influenced seasonal movement patterns. Data were analysed over three spatial scales to allow firm interpretations regarding resource selection. Pythons exhibited distinct seasonal trends in habitat use. During the cooler spring months, snakes chose warm, well‐insulated microhabitats, primarily rocky outcrops on north‐ and north‐west‐facing hillsides. Pythons moved widely during the summer months, apparently in search of prey. Snake localities could be readily linked to rabbit distribution at this time. Specifically, snakes moved to more open, disturbed habitats that contained a high density of rabbits, and consistently selected microhabitats in close proximity to rabbit burrows. In autumn, habitat use was transitional, as snakes progressively returned to the rocky hillsides where they overwintered. Thus, trends in habitat use were influenced by the snakes' thermoregulatory and foraging strategies. Careful management of specific habitats and feral prey populations is required to conserve populations of this endangered snake.     

Effects of External Mass Transfer and Product Inhibition on a Simulated Immobilized Enzyme‐Catalyzed Reactor for Lactose Hydrolysis

A mathematical model has been developed for predicting the performance and simulation of a packed bed immobilized enzyme reactor performing lactose hydrolysis, which follows Michaelis‐Menten kinetics with competitive product (galactose) inhibition. The performance characteristics of a packed bed immobilized enzyme reactor have been analyzed taking into account the effects of various diffusional phenomena like axial dispersion and external mass transfer limitations. The model design equations are then solved by Galerkin's method and orthogonal collocation on finite elements. The effects of external mass transfer and axial dispersion have been studied and their effects were shown to reduce the external effectiveness factor. The effects of product inhibition have been investigated at different operating conditions correlated at different regimes using dimensionless moduli (St, γ, θ, Da)¹⁾. The product inhibition was shown to reduce the substrate conversion, and, additionally, to decrease the effectiveness factor when Da > Da_xo, however, it increases the effectiveness factor when Da < Da_xo. The effectiveness factor is found to be independent of the product inhibition at a crossover point at which Da_xo is defined. Effects of St and Pe have been investigated at different kinetic regimes and the results show that their effects have a strong dependency on the kinetic parameters θ, γ (i.e., K_m/K_p), and Da_xo.     

在中国应用垂直波束雷达监测褐飞虱和其他水稻害虫迁飞的可行性

近年来,可用于昆虫迁飞研究且可自动运行的垂直波束雷达(vertical-looking radar,VLR)的发展使得对迁飞性害虫的周年长期自动监测成为可能。本文提供了我们对能否将这种雷达应用于中国的褐飞虱和其他水稻害虫的监测与预测体系以改善其综合治理的可行性研究结果。以往的研究已经表明,这些害虫一般在300—2000m高度迁飞;而我们根据褐飞虱的雷达和射有效截面的计算结果表明,目前使用的3．2cm波长的VLR对褐飞虱个体目标的最大可检测高度仅约240m;虽然建造一部8．8mm波长的VLR即可覆盖褐飞虱迁飞高度的绝大部分,但其造价和维护费用均过于昂贵。为此,一个更可行的解决方案是,以3．2cm波长的VLR作为包括大多数水稻害虫在内的个体较大的迁飞性害虫的监测工具。     

Evolution of duplicate genes in a tetraploid animal, Xenopus laevis

To understand the evolution of duplicate genes, we compared rates of nucleotide substitution between 17 pairs of nonallelic duplicated genes in the tetraploid frog Xenopus laevis with rates between the orthologous loci of human and rodent. For all duplicated X. laevis genes, the number of synonymous substitutions per site (dS) was greater than the number of nonsynonymous substitutions per site (dN), indicating that these genes are subject to purifying selection. There was also a significant positive correlation (r = 0.915) between dN for the X. laevis genes and dN for the mammalian genes, suggesting that, at the amino acid level, the X. laevis genes and the mammalian genes are under similar constraints. Results of relative-rate tests showed nearly equal rates of nonsynonymous substitution in each copy of the X. laevis genes; apparently there are similar constraints on both copies. No correlation was found between dS for the X. laevis genes and dS for the mammalian genes. There was a significant positive correlation both between members of pairs of duplicated X. laevis genes (r = 0.951) and between human and rodent orthologues (r = 0.854) with respect to third- position G+C content but no such relationship between the X. laevis genes and either of their mammalian orthologues. The results indicate that both copies of a duplicate gene can be subject to purifying selection and thus support the hypothesis of selection against all genotypes containing a null allele at either of two duplicate loci.      

Annual cycles of water vapour and carbon dioxide fluxes in and above a boreal aspen forest

Water vapour and CO₂ fluxes were measured using the eddy correlation method above and below the overstorey of a 21-m tall aspen stand in the boreal forest of central Saskatchewan as part of the Boreal Ecosystem-Atmosphere Study (BOREAS). Measurements were made at the 39.5-m and 4-m heights using 3-dimensional sonic anemometers (Kaijo-Denki and Solent, respectively) and closed-path gas analysers (LI-COR 6262) with 6-m and 4.7-m long heated sampling tubing, respectively. Continuous measurements were made from early October to mid-November 1993 and from early February to late-September 1994. Soil CO₂ flux (respiration) was measured using a LI-COR 6000-09 soil chamber and soil evaporation was measured using Iysimetry. The leaf area index of the aspen and hazelnut understorey reached 1.8 and 3.3, respectively. The maximum daily evapotranspiration (E) rate was 5–6 mm d^?1. Following leaf-out the hazelnut and soil accounted for 22% of the forest E. The estimated total E was 403 mm for 1994. About 88% of the precipitation in 1994 was lost as evapotranspiration. During the growing season, the magnitude of half-hourly eddy fluxes of CO₂ from the atmosphere into the forest reached 1.2 mg CO₂ m^?2 s^?1 (33 μmol C m^?2 s^?1) during the daytime. Downward eddy fluxes at the 4-m height were observed when the hazelnut was growing rapidly in June and July. Under well-ventilated night-time conditions, the eddy fluxes of CO₂ above the aspen and hazelnut, corrected for canopy storage, increased exponentially with soil temperature at the 2-cm depth. Estimates of daytime respiration rates using these relationships agreed well with soil chamber measurements. During the 1994 growing season, the cumulative net ecosystem exchange (NEE) was -3.5 t C ha^?1 y^?1 (a net gain by the system). For 1994, cumulative NEE, ecosystem respiration (R) and gross ecosystem photosynthesis (GEP = R - NEE) were estimated to be -1.3, 8.9 and 10.2 t C ha^?1 y^?1 respectively. Gross photosynthesis of the hazelnut was 32% of GEP.     

Response to Saturation Deficit of Leaf Extension in a Stand of Pearl Millet (Pennisetum typhoides S. & H.)II: II. DEPENDENCE ON LEAF WATER STATUS AND IRRADIANCE

This paper describes how the dominant relation between leafextension and temperature in pearl millet is modified by atmosphericsaturation vapour pressure deficit (SD) and irradiance. Standsof plants were grown at two levels of SD and soil moisture content.Leaf extension, water potential (₁) and stomatal conductancewere all reduced at high SD, ₁ was more closely related to transpirationrate than to SD itself. Leaf extension rate (R) was poorly correlatedwith ₁, even after correction for temperature differences, owingto variation in solute potential between leaves. However, Rin individual leaves was linearly related to turgor potential,except after periods of low irradiance. The thermal time conceptwas modified to incorporate turgor potential and used to showthat the ‘turgor thermal rate of extension’ decreasedsharply at low irradiances, presumably due to assimilate shortage. Key words: Extension, Saturation deficit, Millet     

Cell surface distribution and intracellular fate of asialoglycoproteins: a morphological and biochemical study of isolated rat hepatocytes and monolayer cultures

A combination of biochemistry and morphology was used to demonstrate that more than 95 percent of the isolated rat hepatocytes prepared by collagenase dissociation of rat livers retained the pathway for receptor-mediated endocytosis of asialoglycoproteins (ASGPs). Maximal specific binding of (125)I-asialoorosomucoid ((125)I-ASOR) to dissociated hepatocytes at 5 degrees C (at which temperature no internalization occurred) averaged 100,000-400,000 molecules per cell. Binding, uptake, and degredation of (125)I- ASOR at 37 degrees C occurred at a rate of 1 x 10(6) molecules per cell over 2 h. Light and electron microscopic autoradiography (LM- and EM-ARG) of (125)I-ASOR were used to visualize the surface binding sites at 5 degrees C and the intracellular pathway at 37 degrees C. In the EM-ARG experiments, ARG grains corresponding to (125)I-ASOR were distributed randomly over the cell surface at 5 degrees C but over time at 37 degrees C were concentrated in the lysosome region. Cytochemical detection of an ASOR-horseradish peroxidase conjugate (ASOR-HRP) at the ultrastructural level revealed that at 5 degrees C this specific ASGP tracer was concentrated in pits at the cell surface as well as diffusely distributed along the rest of the plasma membrane. Such a result indicates that redistribution of ASGP surface receptors had occurred. Because the number of surface binding sites of (125)I-ASOR varied among cell preparations, the effect of collagenase on (125)I-ASOR binding was examined. When collagenase-dissociated hepatocytes were re-exposed to collagenase at 37 degrees C, 10-50 percent of control binding was observed. However, by measuring the extent of (125)I-ASOR binding at 5 degrees C in the same cell population before and after collagenase dissociation, little reduction in the number of ASGP surface receptors was found. Therefore, the possibility that the time and temperature of the cell isolations allowed recovery of cell surface receptors following collagenase exposure was tested. Freshly isolated cells, dissociated cells that were re-exposed to collagenase, and perfused livers exposed to collagenase without a Ca(++)-free pre-perfusion, were found to bind 110-240 percent more(125)I-ASOR after 1 h at 37 degrees C that they did at 0 time. This recovery of surface ASGP binding activity occurred in the absence of significant protein synthesis (i.e., basal medium or 1 mM cycloheximide). Suspensions of isolated, unpolarized hepatocytes were placed in monolayer culture for 24 h and confluent cells were demonstrated to reestablish morphologically distinct plasma membrane regions analogous to bile canalicular, lateral, and sinusoidal surfaces in vivo. More than 95 percent of these cells maintained the capacity to bind, internalize, and degrade (125)I-ASOR at levels comparable to those of the freshly isolated population. ASOR-HRP (at 5 degrees C) was specifically bound to all plasma membrane surfaces of repolarized hepatocytes (cultured for 24 h) except those lining bile canalicular-like spaces. Thus, both isolated, unpolarized hepatocytes and cells cultured under conditions that promote morphological reestablishment of polarity maintain the pathway for receptor- mediated endocytosis of ASGPs.