Covariation between colony social structure and immune defences of workers in the ant Formica selysi

Several ant species vary in the number of queens per colony, yet the causes and consequences of this variation remain poorly understood. In previous experiments, we found that Formica selysi workers originating from multiple-queen (=polygyne) colonies had a lower resistance to a fungal pathogen than workers originating from single-queen (=monogyne) colonies. In contrast, group diversity improved disease resistance in experimental colonies. This discrepancy between field and experimental colonies suggested that variation in social structure in the field had antagonistic effects on worker resistance, possibly through a down-regulation of the immune system balancing the positive effect of genetic diversity. Here, we examined if workers originating from field colonies with alternative social structure differed in three major components of their immune system. We found that workers from polygyne colonies had a lower bacterial growth inhibitory activity than workers from monogyne colonies. In contrast, workers from the two types of colonies did not differ significantly in bacterial cell wall lytic activity and prophenoloxidase activity. Overall, the presence of multiple queens in a colony correlated with a slight reduction in one inducible component of the immune system of individual workers. This reduced level of immune defence might explain the lower resistance of workers originating from polygyne colonies despite the positive effect of genetic diversity. More generally, these results indicate that social changes at the group level can modulate individual immune defence

Experimentally increased group diversity improves disease resistance in an ant species.

A leading hypothesis linking parasites to social evolution is that more genetically diverse social groups better resist parasites. Moreover, group diversity can encompass factors other than genetic variation that may also influence disease resistance. Here, we tested whether group diversity improved disease resistance in an ant species with natural variation in colony queen number. We formed experimental groups of workers and challenged them with the fungal parasite Metarhizium anisopliae. Workers originating from monogynous colonies (headed by a single queen and with low genetic diversity) had higher survival than workers originating from polygynous ones, both in uninfected groups and in groups challenged with M. anisopliae. However, an experimental increase of group diversity by mixing workers originating from monogynous colonies strongly increased the survival of workers challenged with M. anisopliae, whereas it tended to decrease their survival in absence of infection. This experiment suggests that group diversity, be it genetic or environmental, improves the mean resistance of group members to the fungal infection, probably through the sharing of physiological or behavioural defences

Cotton cultivation in Laos

Le Laos est un pays de tradition cotonnière, dont les systèmes de culture sont adaptés à de multiples situations écologiques. Ils comprennent en particulier le riz, le cotonnier, l'arachide. Afin qu'une véritable filière cotonnière, source de devises pour le pays, puisse être développée, les recherches du projet de coopération bilatérale franco-lao de recherche-développement sur les plantes à fibre ont porté sur des systèmes de culture améliorés, comprenant engrais et pesticides, techniques de culture plus performantes et variétés productives. Dans les villages, des structures artisanales d'égrenage et de pressage de la fibre s'organisent, en plus de l'usine de filature installée à Vientiane. Dans certaines régions proches de la Thaïlande, la culture cotonnière d'exportation se développe avec des variétés améliorée

Transport and conservation laws

We study the lowest order conservation laws in one-dimensional (1D) integrable quantum many-body models (IQM) as the Heisenberg spin 1/2 chain, the Hubbard and t-J model. We show that the energy current is closely related to the first conservation law in these models and therefore the thermal transport coefficients are anomalous. Using an inequality on the time decay of current correlations we show how the existence of conserved quantities implies a finite charge stiffness (weight of the zero frequency component of the conductivity) and so ideal conductivity at finite temperatures.Comment: 6 pages, Late

Time evolution of a quantum many-body system: transition from integrability to ergodicity in thermodynamic limit

Numerical evidence is given for non-ergodic (non-mixing) behavior, exhibiting ideal transport, of a simple non-integrable many-body quantum system in the thermodynamic limit, namely kicked $t-V$ model of spinless fermions on a ring. However, for sufficiently large kick parameters $t$ and $V$ we recover quantum ergodicity, and normal transport, which can be described by random matrix theory.Comment: 4 pages in RevTex (6 figures in PostScript included

Electron spin resonance in high-field critical phase of gapped spin chains

Motivated by recent experiments on Ni(C_{2}H_{8}N_{2})_{2}Ni(CN)_{4} (commonly known as NENC), we study the electron spin resonance in the critical high-field phase of the antiferromagnetic S=1 chain with strong planar anisotropy and show that the ESR spectra exhibit several peculiarities in the critical phase. Possible relevance of those results for other gapped spin systems is discussed.Comment: 8 revtex pages, 1 eps figure include

Transport in the XX chain at zero temperature: Emergence of flat magnetization profiles

We study the connection between magnetization transport and magnetization profiles in zero-temperature XX chains. The time evolution of the transverse magnetization, m(x,t), is calculated using an inhomogeneous initial state that is the ground state at fixed magnetization but with m reversed from -m_0 for x0. In the long-time limit, the magnetization evolves into a scaling form m(x,t)=P(x/t) and the profile develops a flat part (m=P=0) in the |x/t|1/2 while it expands with the maximum velocity, c_0=1, for m_0->0. The states emerging in the scaling limit are compared to those of a homogeneous system where the same magnetization current is driven by a bulk field, and we find that the expectation values of various quantities (energy, occupation number in the fermionic representation) agree in the two systems.Comment: RevTex, 8 pages, 3 ps figure

Emotion beliefs and cognitive behavioural therapy for social anxiety disorder

Despite strong support for the efficacy of cognitive behavioural therapy (CBT) for social anxiety disorder (SAD), little is known about mechanisms of change in treatment. Within the context of a randomized controlled trial of CBT, this study examined patients' beliefs about the fixed versus malleable nature of anxiety-their 'implicit theories'-as a key variable in CBT for SAD. Compared to waitlist (n = 29; 58% female), CBT (n = 24; 52% female) led to significantly lower levels of fixed beliefs about anxiety (Mbaseline = 11.70 vs. MPost = 7.08, d = 1.27). These implicit beliefs indirectly explained CBT-related changes in social anxiety symptoms (κ(2) = .28, [95% CI = 0.12, 0.46]). Implicit beliefs also uniquely predicted treatment outcomes when controlling for baseline social anxiety and other kinds of maladaptive beliefs (perceived social costs, perceived social self-efficacy, and maladaptive interpersonal beliefs). Finally, implicit beliefs continued to predict social anxiety symptoms at 12 months post-treatment. These findings suggest that changes in patients' beliefs about their emotions may play an important role in CBT for SAD

Finite temperature mobility of a particle coupled to a fermion environment

We study numerically the finite temperature and frequency mobility of a particle coupled by a local interaction to a system of spinless fermions in one dimension. We find that when the model is integrable (particle mass equal to the mass of fermions) the static mobility diverges. Further, an enhanced mobility is observed over a finite parameter range away from the integrable point. We present a novel analysis of the finite temperature static mobility based on a random matrix theory description of the many-body Hamiltonian.Comment: 11 pages (RevTeX), 5 Postscript files, compressed using uufile