Small population instability and island settlement patterns

A model of extinction probability, based on the general theory of island biogeography [MacArthur and Wilson, 1967], is proposed for humans on oceanic islands; extinction probability is determined by island carrying capacity, frequency and amplitude of fluctuations in resources determining carrying capacity, and the net costs of contact and exchange between population units. The model predicts that extinction probability will determine island settlement patterns within an island group resulting in nonsettlement of islands with low carrying capacities and settlement of all islands with high carrying capacities. Data examined from the Marshall Islands tend to support the model. The model is extended to initial atoll colonization patterns. Possible requirements for initial settlement are suggested.Deceased.     

The permeability coefficient of the wall of a villous membrane

Summary The equations hitherto used to correct the permeability coefficient for the unstirred layer influence are valid only for flat membranes. Therefore, appropriate equations for membranes with a villous surface (e.g., small intestine) have been derived. They take into account the non-linear concentration gradient in the intervillous part of the unstirred layer. Quantitative information about the geometry of the villous surface and the unstirred layer thickness are needed to calculate the permeability coefficient of the membrane wall (e.g., intestinal epithelium). The concentration of highly permeable substances drops sharply already in the upper part of the intervillous space, so that the tips of the villi function as effective absorbing area. The intervillous concentration gradient of a substance with a low permeability coefficient is so small, that such a substance is absorbed by the total surface area of the villous membrane. The effective absorbing area of substances with intermediate permeability coefficient lies between the described limits.     

Permeability characteristics of muscle membrane

Unidirectional flux rates of saturated fatty acids, saturated alcohols, and bile acids were measured in an intact rat diaphragm preparation. The logarithm of the permeability coefficients for fatty acids containing from five to ten carbon atoms was a linear function of the number of carbon atoms in the fatty acid chain. Incremental free energies of solution were +336 cal · mol⁻¹ for the addition of a hydroxyl group and −258 cal · mol⁻¹ for the addition of a methylene group. These incremental free energies were similar to those obtained by other investigators in other animal tissues, and our data suggest a structural similarity between membranes in different tissues and in different species. The muscle membrane exhibited anomalously high permeabilities for fatty acids containing less than five carbon atoms. Since muscle lacks tight junctions, this result suggests that small non-electrolytes traverse polar regions or aqueous pores within the cellular membrane.     

Pressure-induced changes in the molecular organization of a lipid-peptide complex. Polymyxin binding to phosphatidic acid membranes

The effect of 100 atm pressure on the organization of the lipid-peptide complex formed between polymyxin and dipalmitoyl phosphatidic acid has been investigated. Phase transition curves were obtained by electron paramagnetic resonance by measuring the partition coefficient of the spin label, 2, 2, 5, $\text{5-}\text{tetramethylpiperidine}\text{-N-}\text{oxyl}$. The three-step phase transition curve previously obtained with fluorescence polarization measurements was confirmed, demonstrating three distinct phosphatidic acid domains in the bilayer. Pressure increases binding of polymyxin to phosphatidic acid bilayers and alters the proportions of the two domains that differ in the mode of binding between phosphatidic acid and polymyxin. The binding curves of polymyxin to phosphatidic acid bilayers were determined and it was shown that application of pressure reduces the cooperativity of the binding curve.     

Nutrient inflows into apple roots. I. 32P-orthophosphate uptake from solution by M.9 rootstocks and Worcester Pearmain seedlings

Abstract. The rates of uptake of ³²P-labelled orthophosphate by whole root systems of young apple trees (M.9 rootslocks and Worcester Pearmain seedlings) were measured in solution culture. Using a solution depletion technique, the ³²P-phosphate uptake rates per unit length, surface area or fresh weight of roots were determined as a function of ³²P-phosphate concentration in solution at the root surface over the range 0.25–10 mmol m⁻³. The effect of P concentration within various plant parts on the relation between uptake rate and external P concentration was studied using plants differing in internal P levels.
The apparent minimutn P concentration below which P uptake ceased was of the order of 0.25–0.50 mmol m⁻³. Fluxes, inflows and unit absorption rates increased approximately proportionately with solution concentration up to 10mmolm⁻³. Except perhaps in the case of the low-P M.9 plant, there was no evidence of a diminishing returns type of relationship over the range of solution concentrations examined. The threshold P concentration in solution above which uptake rates cease to increase thus appears to be higher for apples than for other species.
At any given P concentration, fluxes, inflows and unit absorption rates were higher for M.9 than for Worcester and for low-P plants than for high-P plants. The difference between plants of different P status was more marked for M.9 and seems to be more closely related to shoot P levels than to root P.     

Quasi-elastic light scattering of Artemia ribosomes sedimented in a CsCl density gradient

It is impossible to measure the diffusion coefficient of macromolecules directly and accurately by quasi—elastic light scattering, when aggregates cannot be eliminated from the solutions to be investigated. Nevertheless, a simple method can be applied to overcome this problem in many cases. Aggregates are separated from the monomeric macromolecules by rate-zonal sedimentation in a CsCl density gradient in a transparent centrifugation tube; the monomers are then located by laser light scattering intensity measurements; photon correlation spectroscopy of the scattered light finally yields their diffusion coefficient. The viscosity of aqueous CsCl solutions at different temperatures and concentrations allows a good separation by centrifugation and a low uncertainty in the reduction of the measured diffusion coefficient to standard conditions.The application of the method to eukaryotic large ribosomal subunits is described as an example.     

Estimation of growth yield and maintenance coefficient of plant cell suspensions

Methodology is presented for the determination of growth yield (Y(g)) and maintenance coefficient (m) for carbon utilization of plant cells grown in suspension culture. Estimation of Y(g) and m requires measurements of specific growth rate (micro) and specific rate of substrate uptake (q) at different growth limiting substrate concentrations. Batch culture of tobacco cells did not permit evaluation of Y(g) and m because micro is constant and maximal during most of the growth cycle. In batch culture, the period of declining specific growth rate is extremely brief because of the rapid transition from logarithmic growth to stationary phase. This occurs because the K(m) for growth is relatively small compared to the initial sucrose concentration. Thus, when the substrate level reaches the K(m), the large mass of cells rapidly depletes the remaining substrate. In contrast, semicontinuous culture facilitates the determination of Y(g) and m because various steady-state growth rates can be achieved. Mathematical expressions were developed to determine the effective values of micro and q over the semicontinuous replacement interval. The validity of this approach was verified by conducting simulations using experimentally determined parameters.     

Effects of temperature on acaricidal and insecticidal activities of the benzoylureas flucycloxuron and diflubenzuron

Effects of temperature on the activity of flucycloxuron on larval stages of Panonychus ulmi (Koch), based on LC₅₀ values, were highly significant (P < 0.001) with temperature coefficients of-1.7 in both the ranges of 15° to 25°C and 20° to 30°C. The slopes of probit regression lines at 15° and 20°C were significantly steeper than those at 25° and 30°C. As a consequence the temperature coefficients based on LC₉₀ values were-4.4 and-2.2, for the 2 temperature ranges. The ovicidal activity of flucycloxuron on P. ulmi was low and was only statistically detectable at 20°C (LC₉₀ of 84 mg a.i./l). In studies with larvae of Aedes aegypti (Linnaeus), Leptinotarsa decemlineata (Say), Plutella xylostella (Linnaeus), Spodeptera exigua (Hübner) and Spodoptera littoralis (Boisduval) probit regression lines were parallel over temperature. The activity of flucycloxuron on these five insect species was not affected by temperature. Based on LC₅₀ values, diflubenzuron showed positive temperature coefficients on P. xylostella of + 2.1 at 15° to 25°C and + 2.5 at 20° to 30°C. For S. littoralis the temperature coefficient was positive (+ 2.4) at 15° to 25°C but negative (-1.9) at the 20° to 30°C range. Temperature coefficients of diflubenzuron were neutral for A. aegypti, L. decemlineata and S. exigua. In the design and analysis of these studies special allowance was made for date effects and variation in natural mortality over temperature.     

Crossing experiments in Allium L. section Cepa

VAN RAAMSDONK, L. W. D., WIETSMA, W. A. & DE VRIES, J. N., 1992. Crossing experiments in Allium L. section Cepa . A full diallel was carried out with six diploid species of Allium section Cepa and A. roylei of section Rhizirideum , High isolation barriers were found between the related species A. cepa and A. oschaninii , between A. oschaninii and A. vavilovii , and between A. galanthum and A. pskemense . On the contrary, the species A. cepa and A. roylei , belonging to different sections, show only slight isolation barriers. The Wallace effect, which is the development of internal isolation barriers as such, is likely to have taken place in the evolution of A. oschaninii and A. vavilovii , and possibly also between A. galanthum and A. pskemense .     

A small protein in model membranes: a time-resolved fluorescence and ESR study on the interaction of M13 coat protein with lipid bilayers

Model membranes with unsaturated lipid chains containing various amounts of M13 coat protein in the -helical form were studied using time-resolved fluorescence and ESR spectroscopy. The lipid-to-protein (L/P) ratios used were > 12 to avoid protein-protein contacts and irreversible aggregation leading to -polymeric coat protein. In the ESR spectra of the 12-SASL probe in dioleoyl phosphatidylcholine (DOPC) bilayers no second protein induced component is observed upon incorporation of M13 coat protein. However, strong effects are detected on the ESR lineshapes upon changing the protein concentration. The ESR lineshapes are simulated by assuming a fixed ratio between the parallel (D) and perpendicular (D) diffusion coefficients of 4, and an order parameter equal to zero. It is found that increasing the protein concentration from L/P to L/P 15 results in a decrease of the rotational diffusion coefficient D from 3.4 × 10⁷ to 1.9 × 10⁷ s^–1. In the time-resolved fluorescence experiments with DPH-propionic acid as a probe, it is observed that increasing the M13 coat protein concentration causes an increase of the two fluorescent lifetimes, indicating an increase in bilayer order. Analysis of the time-resolved fluorescence anisotropy decay allows one to quantitatively determine the order parameters P₂ and P₄, and the rotational diffusion coefficient D of the fluorescent probe. The order parameters P₂ and P₄ increase from 0.34 to 0.55 and from 0.59 to 0.77, respectively, upon adding M13 coat protein to DOPC bilayers with an L/P ratio of 35. The rotational diffusion coefficient D of the DPH-propionic acid probe decreases on incorporating M13 coat protein, in accordance with the ESR results. It is concluded that M13 coat protein in the -monomeric state is not able to produce a long living lipid boundary shell and consequently an immobilization of the lipids. An overall effect on the lipids is induced, resulting in a reduction in the dynamics and an increase in average lipid order. The hydrophobic region of M13 coat protein is proposed to perfectly match the lipid bilayer, resulting in a relatively small distortion of the bilayer structure of the lipid system.