Marginal speed confinement resolves the conflict between correlation and control in natural flocks of birds

Speed fluctuations of individual birds within natural flocks are moderate, due to the aerodynamic, energetic and biomechanical constraints of flight. Yet the spatial correlations of such fluctuations are scale-free, namely they have a range as wide as the entire group. Scale-free correlations and limited fluctuations set conflicting constraints on the mechanism controlling the speed of each bird, as the factors boosting correlations tend to amplify fluctuations, and vice versa. Here, using a field-theoretical approach, we demonstrate that a marginal speed confinement that ignores small deviations from the natural reference value while ferociously suppressing larger fluctuations, is the only mechanism reconciling scale-free correlations with biologically acceptable flocks' speed, a result that we confirm through numerical simulations on self-propelled particles in three dimensions. We validate the theoretical as well as the numerical predictions of this analysis by comparing our results with field experimental data on starling flocks having group sizes spanning an unprecedented interval of over two orders of magnitude

Marginal speed confinement resolves the conflict between correlation and control in natural flocks of birds

Speed fluctuations of individual birds in natural flocks are moderate, due to the aerodynamic and biomechanical constraints of flight. Yet the spatial correlations of such fluctuations are scale-free, namely they have a range as wide as the entire group, a property linked to the capacity of the system to collectively respond to external perturbations. Scale-free correlations and moderate fluctuations set conflicting constraints on the mechanism controlling the speed of each agent, as the factors boosting correlation amplify fluctuations, and vice versa. Here, using a statistical field theory approach, we suggest that a marginal speed confinement that ignores small deviations from the natural reference value while ferociously suppressing larger speed fluctuations, is able to reconcile scale-free correlations with biologically acceptable group's speed. We validate our theoretical predictions by comparing them with field experimental data on starling flocks with group sizes spanning an unprecedented interval of over two orders of magnitude.Comment: 18 pages, 5 figures. Latest version before publication uploaded, journal reference adde

Dual RNA-seq of Orientia tsutsugamushi informs on host-pathogen interactions for this neglected intracellular human pathogen.

Studying emerging or neglected pathogens is often challenging due to insufficient information and absence of genetic tools. Dual RNA-seq provides insights into host-pathogen interactions, and is particularly informative for intracellular organisms. Here we apply dual RNA-seq to Orientia tsutsugamushi (Ot), an obligate intracellular bacterium that causes the vector-borne human disease scrub typhus. Half the Ot genome is composed of repetitive DNA, and there is minimal collinearity in gene order between strains. Integrating RNA-seq, comparative genomics, proteomics, and machine learning to study the transcriptional architecture of Ot, we find evidence for wide-spread post-transcriptional antisense regulation. Comparing the host response to two clinical isolates, we identify distinct immune response networks for each strain, leading to predictions of relative virulence that are validated in a mouse infection model. Thus, dual RNA-seq can provide insight into the biology and host-pathogen interactions of a poorly characterized and genetically intractable organism such as Ot