The role of endosymbionts in the evolution of haploid-male genetic systems in scale insects (Coccoidea)

There is an extraordinary diversity in genetic systems across species, but this variation remains poorly understood. In part, this is because the mechanisms responsible for transitions between systems are often unknown. A recent hypothesis has suggested that conflict between hosts and endosymbiotic microorganisms over transmission could drive the transition from diplodiploidy to systems with male haploidy (haplodiploidy, including arrhenotoky and paternal genome elimination [PGE]). Here, we present the first formal test of this idea with a comparative analysis across scale insects (Hemiptera: Coccoidea). Scale insects are renowned for their large variation in genetic systems, and multiple transitions between diplodiploidy and haplodiploidy have taken place within this group. Additionally, most species rely on endosymbiotic microorganisms to provide them with essential nutrients lacking in their diet. We show that species harboring endosymbionts are indeed more likely to have a genetic system with male haploidy, which supports the hypothesis that endosymbionts might have played a role in the transition to haplodiploidy. We also extend our analysis to consider the relationship between endosymbiont presence and transitions to parthenogenesis. Although in scale insects there is no such overall association, species harboring eukaryote endosymbionts were more likely to be parthenogenetic than those with bacterial symbionts. These results support the idea that intergenomic conflict can drive the evolution of novel genetic systems and affect host reproduction.Peer reviewe

Heating of the intergalactic medium due to structure formation

We estimate the heating of the intergalactic medium due to shocks arising from structure formation. Heating of the gas outside the collapsed regions, with small overdensities (${n_b \over {\bar n_b}}\ll 200$) is considered here, with the aid of Zel'dovich approximation. We estimate the equation of state of this gas, relating the density with its temperature, and its evolution in time, considering the shock heating due to one-$\sigma$ density peaks as being the most dominant. We also estimate the mass fraction of gas above a given temperature as a function of redshift. We find that the baryon fraction above $10^6$ K at $z=0$ is $\sim 10$. We estimate the integrated Sunyaev-Zel'dovich distortion from this gas at present epoch to be of order $10^{-6}$.Comment: 5 pages (3 figs), To appear in MNRAS (pink pages

What trends in energy efficiencies? Evidence from a robust test

A proper modeling of the long-run behavior of energy and oil intensities is crucial in many respects. This paper aims at checking whether this long-run behavior should be modelled as a deterministic or a stochastic trend or both. We first apply a test for a deterministic trend robust to uncertainty about the stochastic trend. Our results indicate that, for the period 1960–2004, energy intensities of only 8 OECD countries out of 25 include a negative deterministic trend, 3 include a positive one and 14 seem to be better modelled by a stochastic trend only. When considering a sample of 73 non-OECD countries on the period 1971–2004, we show that only 22 exhibit a deterministic trend (negative for 15 countries and positive for 7 countries). Asimilar analysis for oil intensity leads to reject the hypothesis of an insignificant deterministic trend for 7 OECD countries out of 23 for the period 1965–2004 and 11 non-OECD countries out of 40 for the period 1971–2004. In the next step, we apply standard unit root tests and find that the unit root hypothesis is not very often rejected. We conclude that a main feature of energy intensities is the presence of a stochastic trend

On the non-convergence of energy intensities: Evidence from a pair-wise econometric approach

This paper evaluates the convergence of energy intensities for a group of 97 countries in the period 1971–2003. Convergence is tested using a recent method proposed by Pesaran (2007) [Pesaran, M.H., 2007. A pair-wise approach to testing for output and growth convergence. Journal of Econometrics 138, 312–355] based on the stochastic convergence criterion. An advantage of this method is that results do not depend on a benchmark against which convergence is assessed. It gives more robust results. Applications of several unit-root tests as well as a stationarity test uniformly reject the global convergence hypothesis. Locally, for Middle East, OECD and Europe sub-groups, non-convergence is less strongly rejected. The introduction of possible structural breaks in the analysis only marginally provides more support to the convergence hypothesis.ou

Likelihood Analysis of Cosmic Shear on Simulated and VIRMOS-DESCART Data

We present a maximum likelihood analysis of cosmological parameters from measurements of the aperture mass up to 35 arcmin, using simulated and real cosmic shear data. A four-dimensional parameter space is explored which examines the mean density \Omega_M, the mass power spectrum normalization \sigma_8, the shape parameter \Gamma and the redshift of the sources z_s. Constraints on \Omega_M and \sigma_8 (resp. \Gamma and z_s) are then given by marginalizing over \Gamma and z_s (resp. \Omega_M and \sigma_8). For a flat LCDM cosmologies, using a photometric redshift prior for the sources and \Gamma \in [0.1,0.4], we find \sigma_8=(0.57\pm0.04) \Omega_M^{(0.24\mp 0.18) \Omega_M-0.49} at the 68% confidence level (the error budget includes statistical noise, full cosmic variance and residual systematic). The estimate of \Gamma, marginalized over \Omega_M \in [0.1,0.4], \sigma_8 \in [0.7,1.3] and z_s constrained by photometric redshifts, gives \Gamma=0.25\pm 0.13 at 68% confidence. Adopting h=0.7, a flat universe, \Gamma=0.2 and \Omega_m=0.3 we find \sigma_8=0.98 \pm0.06 . Combined with CMB, our results suggest a non-zero cosmological constant and provide tight constraints on \Omega_M and \sigma_8. We finaly compare our results to the cluster abundance ones, and discuss the possible discrepancy with the latest determinations of the cluster method. In particular we point out the actual limitations of the mass power spectrum prediction in the non-linear regime, and the importance for its improvement.Comment: 11 pages, submitted to A&

Generating Cosmological Gaussian Random Fields

We present a generic algorithm for generating Gaussian random initial conditions for cosmological simulations on periodic rectangular lattices. We show that imposing periodic boundary conditions on the real-space correlator and choosing initial conditions by convolving a white noise random field results in a significantly smaller error than the traditional procedure of using the power spectrum. This convolution picture produces exact correlation functions out to separations of L/2, where L is the box size, which is the maximum theoretically allowed. This method also produces tophat sphere fluctuations which are exact at radii $R \le L/4$. It is equivalent to windowing the power spectrum with the simulation volume before discretizing, thus bypassing sparse sampling problems. The mean density perturbation in the volume is no longer constrained to be zero, allowing one to assemble a large simulation using a series of smaller ones. This is especially important for simulations of Lyman-$\alpha$ systems where small boxes with steep power spectra are routinely used. We also present an extension of this procedure which generates exact initial conditions for hierarchical grids at negligible cost.Comment: 12 pages incl 3 figures, accepted in ApJ Letter