SPATIAL VARIATION IN SELECTIVE REGIMES: SEXUAL SELECTION IN THE WATER STRIDER,GERRIS ODONTOGASTER

Studies of phenotypic selection in natural populations are often concerned with simply detecting selection. In adopting a more mechanistic approach, this study compares the sexual selection regimes in natural populations of the water strider Gerris odontogaster with a priori predictions of selection, based on a number of previous field and laboratory studies of the behavioral mechanisms of selection. In this species, a general reluctance of females to mate allows for intersexual selection for ability to subdue reluctant females in males. Female reluctance to mate has been shown to decrease with increasing population density, suggesting that sexual selection should be weaker in high density populations. Three different populations with large differences in population density were studied. A number of traits including parasite load, body mass, body size and male abdominal process length were found to experience significant sexual selection. The investigated populations differed considerably with regard to the total strength of selection on the measured traits and the form of selection on single traits. In general, males in the population with the highest density experienced the weakest selection for grasping ability. This pattern is ascribed to density-related alterations of female mating behavior. Selection for male grasping ability, as reflected by selection on male abdominal process length, is reduced in high-density populations where reluctant females are more easily subdued. Further, the studied populations differed significantly in mean phenotype and phenotypic variance for male abdominal process length. It is suggested that interpopulational differences in selective regimes may generate local adaptations with respect to male abdominal process length, and that gene flow may contribute to the maintenance of the high genetic variation in this trait. It is further suggested that more empirical effort should be made in quantifying and understanding spatial and temporal variation in selection in natural populations, since this may provide information on the prevalence of local adaptations in metric traits and on the mechanisms of selection.     

A non-iterative confidence interval estimating procedure for the intraclass kappa statistic with multinomial outcomes

We obtain the asymptotic sample variance of the intraclass kappa statistic for multinomial outcome data. A modified Wald type procedure based on this theory is then used for confidence interval construction. The results of a simulation study show that the proposed non-iterative approach performs very well in terms of confidence interval coverage and width for samples as small as 50. The procedure is illustrated with two examples from previously published medical studies.     

Exact tests for one sample correlated binary data

In this paper we developed exact tests for one sample correlated binary data whose cluster sizes are at most two. Although significant progress has been made in the development and implementation of the exact tests for uncorrelated data, exact tests for correlated data are rare. Lack of a tractable likelihood function has made it difficult to develop exact tests for correlated binary data. However, when cluster sizes of binary data are at most two, only three parameters are needed to characterize the problem. One parameter is fixed under the null hypothesis, while the other two parameters can be removed by both conditional and unconditional approaches, respectively, to construct exact tests. We compared the exact and asymptotic p-values in several cases. The proposed method is applied to real-life data.     

Protein oligomerization through domain swapping: role of inter-molecular interactions and protein concentration

Domain swapping has been shown to be an important mechanism controlling multiprotein assembly and has been suggested recently as a possible mechanism underlying protein aggregation. Understanding oligomerization via domain swapping is therefore of theoretical and practical importance. By using a symmetrized structure-based (Gō) model, we demonstrate that in the free-energy landscape of domain swapping, a large free-energy barrier separates monomeric and domain-swapped dimeric configurations. We investigate the effect of finite monomer concentration, by implementing a new semi-analytical method, which involves computing the second virial coefficient, a thermodynamic indicator of inter-molecular interactions. This method, together with the symmetrized structure-based (Gō) model, minimizes the need for expensive many-protein simulations, providing a convenient framework to investigate concentration effect. Finally, we perform direct simulations of domain-swapped trimer formation, showing that this modeling approach can be used for higher-order oligomers.     

Yeast glycolytic oscillations that are not controlled by a single oscillophore: a new definition of oscillophore strength

Biochemical oscillations, such as glycolytic oscillations, are often believed to be caused by a single so-called ‘oscillophore’. The main characteristics of yeast glycolytic oscillations, such as frequency and amplitude, are however controlled by several enzymes. In this paper, we develop a method to quantify to which extent any enzyme determines the occurrence of oscillations. Principles extrapolated from metabolic control analysis are applied to calculate the control exerted by individual enzymes on the real and imaginary parts of the eigenvalues of the Jacobian matrix. We propose that the control exerted by an enzyme on the real part of the smallest eigenvalue, in terms of absolute value, quantifies to which extent that enzyme contributes to the emergence of instability. Likewise the control exerted by an enzyme on the imaginary part of complex eigenvalues may serve to quantify the extent to which that enzyme contributes to the tendency of the system to oscillate. The method was applied both to a core model and to a realistic model of yeast glycolytic oscillations. Both the control over stability and the control over oscillatory tendency were distributed among several enzymes, of which glucose transport, pyruvate decarboxylase and ATP utilization were the most important. The distributions of control were different for stability and oscillatory tendency, showing that control of instability does not imply control of oscillatory tendency nor vice versa. The control coefficients summed up to 1, suggesting the existence of a new summation theorem. These results constitute proof that glycolytic oscillations in yeast are not caused by a single oscillophore and provide a new, subtle, definition for the oscillophore strength of an enzyme.     

Modifications of Motor Asymmetry in Rats under the Influence of Low-Intensity Extra High-Frequency Electromagnetic Radiation in the Norm and under Stress Conditions

We studied modifications of motor asymmetry in rats with different motor lateralization (dextrals, sinistrals, and ambidextrals) induced by low-intensity extra high-frequency (EHF) electromagnetic radiation (EMR), hypokinetic stress, and their combination. It was found that the development of hypokinetic stress in rats induced by limitation of their mobility results in a considerable decrease of the coefficient of motor asymmetry (up to inversion of its sign); this can be related to a decrease in the resistivity to stressing and adaptability of the organism to the influence of external factors. The influence of EHF EMR on the animals under conditions of both normal and limited motor activity resulted in an increase in the index of motor lateralization in animals of all phenotypic groups under study; probably, this helped to increase the adaptive capabilities of the organism. Neirofiziologiya/Neurophysiology, Vol. 37, No. 2, pp. 164–168, March–April, 2005.     

A simple chlorophyll fluorescence parameter that correlates with the rate coefficient of photoinactivation of Photosystem II

A method of partitioning the energy in a mixed population of active and photoinactivated Photosystem II (PS II) complexes based on chlorophyll fluorescence measurements is presented. There are four energy fluxes, each with its quantum efficiency: a flux associated with photochemical electron flow in active PS II reaction centres (J_{PS II}), thermal dissipation in photoinactivated, non-functional PS IIs (J_NF), light-regulated thermal dissipation in active PS IIs (J_NPQ) and a combined flux of fluorescence and constitutive, light-independent thermal dissipation (J_f,D). The four quantum efficiencies add up to 1.0, without the need to introduce an ‘excess’ term E, which in other studies has been claimed to be linearly correlated with the rate coefficient of photoinactivation of PS II (k_pi). We examined the correlation of k_pi with various fluxes, and found that the combined flux (J_NPQ + J_f,D= J_pi) is as well correlated with k_pi as is E. This combined flux arises from F_s/F_m^′, the ratio of steady-state to maximum fluorescence during illumination, which represents the quantum efficiency of combined non-photochemical dissipation pathways in active PS IIs. Since F_s/F_m^′ or its equivalent, J_pi, is a likely source of events leading to photoinactivation of PS II, we conclude that F_s/F_m^′ is a simple predictor of k_pi.     

A comparative evaluation of oxygen mass transfer and broth viscosity using Cephalosporin-C production as a case strategy

The production of Cephalosporin-C (CPC) a secondary metabolite, using a mold Acremonium chrysogenum was studied in a lab scale Internal loop air lift reactor. Cephalosporin-C production process is a highly aerobic fermentation process. Volumetric gas–liquid mass transfer coefficient (k_La) and viscosity (η) were evaluated, during the growth and production phases of the microbial physiology. An attempt has been made to correlate the broth viscosity, η and volumetric oxygen transfer coefficient, k_La during the Cephalosporin-C production in an air lift reactor. The impact of biomass concentration and mycelial morphology on broth viscosity has been also evaluated. The broth exhibits a typical non-Newtonian fermentation broth. Rheology parameters like consistency index and fluidity index are also studied.     

Clone identification and clonal structure of the European aspen (Populus tremula)

The European aspen (Populus tremula) is thought to reproduce mostly asexually. Thus aspen forms clones, in which several ramets belong to one genetically defined genet. We compared the clonal structure of aspen in old-growth and managed forests in southern and northeastern Finland. Clones were identified using morphological characters and nine microsatellite loci originally developed for Populus tremuloides. There were more clones identified by microsatellites than morphotypes both in old-growth and managed forest. The average size of the clones was only 2.3 ramets and most clones (70%) consisted of just one ramet. The size of the clones showed no difference between managed and old-growth forests or between northeastern and southern Finland. The small size of the clones suggests that most of them are relatively young. Therefore, sexual reproduction may be more common than previously thought. There was an aggregated spatial genetic structure as measured by Moran's I (0-10 m) and by co-ancestry (rho(ij), 0-20 m). Low level of co-ancestry can be explained by relatively unrestricted gene flow, the important role of disturbance in reproduction, and/or local selection.