Costs and benefits of social relationships in the collective motion of bird flocks

This is the author accepted manuscript. The final version is available from Nature Research via the DOI in this record.Supplementary Figs. 1–12 and Supplementary Tables 1–3 are available in the Supplementary Information. Raw images captured by one of the four cameras and the reconstructed birds’ 3D movement trajectories are provided in Supplementary Videos 1–6. Plain text files, each including bird ID number, position, time, velocity, acceleration and wingbeat frequency at every time step, are provided in Supplementary Data 1–7. A plain text file that includes mean wingbeat frequency, flight speed and local density (approximated by the number of neighbours within a distance of 5 m from the focal bird) for paired and unpaired birds in six flocks, as well as for birds flying alone, is provided in Supplementary Data 8. All data required to reproduce the results in this study are included in Supplementary Data 1–8. Supplementary Data and Supplementary Videos are available at https://figshare.com/s/c55eb82bab800571d25d.Current understanding of collective behaviour in nature is based largely on models that assume that identical agents obey the same interaction rules, but in reality interactions may be influenced by social relationships among group members. Here, we show that social relationships transform local interactions and collective dynamics. We tracked individuals’ three-dimensional trajectories within flocks of jackdaws, a species that forms lifelong pair-bonds. Reflecting this social system, we find that flocks contain internal sub-structure, with discrete pairs of individuals tied together by spring-like effective forces. Within flocks, paired birds interacted with fewer neighbours than unpaired birds and flapped their wings more slowly, which may result in energy savings. However, flocks with more paired birds had shorter correlation lengths, which is likely to inhibit efficient information transfer through the flock. Similar changes to group properties emerge naturally from a generic self-propelled particle model. These results reveal a critical tension between individual- and group-level benefits during collective behaviour in species with differentiated social relationships, and have major evolutionary and cognitive implications.Human Frontiers in Science Programm

Simultaneous measurements of three-dimensional trajectories and wingbeat frequencies of birds in the field

This is the author accepted manuscript. The final version is available from the Royal Society via the DOI in this recordData accessibility: We provide data including images recorded by four cameras, camera parameters, videos showing the time variation of the bird 3D positions, and plain text files that include bird id number, positions, times, velocities, accelerations, and wingbeat frequencies at every time step. We also provide the Matlab codes that were used to: (i) detect birds on images; (ii) reconstruct birds' 3D locations using the new stereo-matching algorithm; (iii) track individual's 3D motions; and (iv) calculate wing motion and wingbeat frequency from tracking results. The code and data are available at: https://github.com/linghj/3DTracking.git and https://figshare.com/s/3c572f91b07b06ed30aa.Tracking the movements of birds in three dimensions is integral to a wide range of problems in animal ecology, behaviour and cognition. Multi-camera stereo-imaging has been used to track the three-dimensional (3D) motion of birds in dense flocks, but precise localization of birds remains a challenge due to imaging resolution in the depth direction and optical occlusion. This paper introduces a portable stereo-imaging system with improved accuracy and a simple stereo-matching algorithm that can resolve optical occlusion. This system allows us to decouple body and wing motion, and thus measure not only velocities and accelerations but also wingbeat frequencies along the 3D trajectories of birds. We demonstrate these new methods by analysing six flocking events consisting of 50 to 360 jackdaws (Corvus monedula) and rooks (Corvus frugilegus) as well as 32 jackdaws and 6 rooks flying in isolated pairs or alone. Our method allows us to (i) measure flight speed and wingbeat frequency in different flying modes; (ii) characterize the U-shaped flight performance curve of birds in the wild, showing that wingbeat frequency reaches its minimum at moderate flight speeds; (iii) examine group effects on individual flight performance, showing that birds have a higher wingbeat frequency when flying in a group than when flying alone and when flying in dense regions than when flying in sparse regions; and (iv) provide a potential avenue for automated discrimination of bird species. We argue that the experimental method developed in this paper opens new opportunities for understanding flight kinematics and collective behaviour in natural environments.Human Frontier Science Progra

Local interactions and their group-level consequences in flocking jackdaws

This is the author accepted manuscript. The final version is available from the Royal Society via the DOI in this recordData accessibility: Data and code are available from the Dryad Digital Repository: https://doi.org/10.5061/dryad.kb8js06As one of nature's most striking examples of collective behaviour, bird flocks have attracted extensive research. However, we still lack an understanding of the attractive and repulsive forces that govern interactions between individuals within flocks and how these forces influence neighbours' relative positions and ultimately determine the shape of flocks. We address these issues by analysing the three-dimensional movements of wild jackdaws (Corvus monedula) in flocks containing 2–338 individuals. We quantify the social interaction forces in large, airborne flocks and find that these forces are highly anisotropic. The long-range attraction in the direction perpendicular to the movement direction is stronger than that along it, and the short-range repulsion is generated mainly by turning rather than changing speed. We explain this phenomenon by considering wingbeat frequency and the change in kinetic and gravitational potential energy during flight, and find that changing the direction of movement is less energetically costly than adjusting speed for birds. Furthermore, our data show that collision avoidance by turning can alter local neighbour distributions and ultimately change the group shape. Our results illustrate the macroscopic consequences of anisotropic interaction forces in bird flocks, and help to draw links between group structure, local interactions and the biophysics of animal locomotion.Human Frontiers in Science Programm

Behavioural plasticity and the transition to order in jackdaw flocks

This is the final version. Available on open access from Nature Research via the DOI in this recordData availability: Raw images captured by one of the four cameras and the reconstructed 3D movement trajectories of the jackdaws are provided in Supplementary Movies 1 to 3. The group density and group order for 154 groups are provided in Supplementary Data 1. Plain text files, each including bird ID number, position, time, and velocity at every time step are provided in Supplementary Data 2 to 4. All data required to reproduce the results in this study are included in Supplementary Data 1 to 4. The data analysis codes (including the self-propelled particle model) to generate all figures in the paper are also provided. Supplementary Data, Supplementary Movies, and data analysis codes are available at: https://figshare.com/s/472d354cc9e823a8f48fCollective behaviour is typically thought to arise from individuals following fixed interaction rules. The possibility that interaction rules may change under different circumstances has thus only rarely been investigated. Here we show that local interactions in flocks of wild jackdaws (Corvus monedula) vary drastically in different contexts, leading to distinct group-level properties. Jackdaws interact with a fixed number of neighbours (topological interactions) when traveling to roosts, but coordinate with neighbours based on spatial distance (metric interactions) during collective anti-predator mobbing events. Consequently, mobbing flocks exhibit a dramatic transition from disordered aggregations to ordered motion as group density increases, unlike transit flocks where order is independent of density. The relationship between group density and group order during this transition agrees well with a generic self-propelled particle model. Our results demonstrate plasticity in local interaction rules and have implications for both natural and artificial collective systems.Human Frontier Science Progra

Collective turns in jackdaw flocks: kinematics and information transfer

This is the author accepted manuscript. The final version is available from The Royal Society via the DOI in this record.The rapid, cohesive turns of bird flocks are one of the most vivid examples of collective behaviour in nature, and have attracted much research. Three-dimensional imaging techniques now allow us to characterize the kinematics of turning and their group-level consequences in precise detail. We measured the kinematics of flocks of wild jackdaws executing collective turns in two contexts: during transit to roosts and anti-predator mobbing. All flocks reduced their speed during turns, probably because of constraints on individual flight capability. Turn rates increased with the angle of the turn so that the time to complete turns remained constant. We also find that context may alter where turns are initiated in the flocks: for transit flocks in the absence of predators, initiators were located throughout the flocks, but for mobbing flocks with a fixed ground-based predator, they were always located at the front. Moreover, in some transit flocks, initiators were far apart from each other, potentially because of the existence of subgroups and variation in individual interaction ranges. Finally, we find that as the group size increased the information transfer speed initially increased, but rapidly saturated to a constant value. Our results highlight previously unrecognized complexity in turning kinematics and information transfer in social animals.Human Frontier Science Progra

The role of speculative trade in market efficiency: Evidence from a betting exchange

Does speculative trade reduce mispricing and help create efficient markets or does it drive prices further from fundamentals? We analyze betting exchange trading on 9,562 UK horse races in 2013 and 2014 to find out. Crucially, as each race is run, the fundamental value of bets is unambiguously revealed. We find that the volume of trade is predictive of fundamentals, suggesting that speculative trade is on average conducive to market efficiency. However, much of this effect is concentrated in the in-running period during races when, even without trade, asset fundamentals would be revealed seconds later

Bacterial microevolution and the Pangenome

The comparison of multiple genome sequences sampled from a bacterial population reveals considerable diversity in both the core and the accessory parts of the pangenome. This diversity can be analysed in terms of microevolutionary events that took place since the genomes shared a common ancestor, especially deletion, duplication, and recombination. We review the basic modelling ingredients used implicitly or explicitly when performing such a pangenome analysis. In particular, we describe a basic neutral phylogenetic framework of bacterial pangenome microevolution, which is not incompatible with evaluating the role of natural selection. We survey the different ways in which pangenome data is summarised in order to be included in microevolutionary models, as well as the main methodological approaches that have been proposed to reconstruct pangenome microevolutionary history

Nongenomic mechanisms of physiological estrogen-mediated dopamine efflux

<p>Abstract</p> <p>Background</p> <p>Neurological diseases and neuropsychiatric disorders that vary depending on female life stages suggest that sex hormones may influence the function of neurotransmitter regulatory machinery such as the dopamine transporter (DAT).</p> <p>Results</p> <p>In this study we tested the rapid nongenomic effects of several physiological estrogens [estradiol (E₂), estrone (E₁), and estriol (E₃)] on dopamine efflux via the DAT in a non-transfected, NGF-differentiated, rat pheochromocytoma (PC12) cell model that expresses membrane estrogen receptors (ERs) α, β, and GPR30. We examined kinase, ionic, and physical interaction mechanisms involved in estrogenic regulation of the DAT function. E₂-mediated dopamine efflux is DAT-specific and not dependent on extracellular Ca²⁺-mediated exocytotic release from vesicular monoamine transporter vesicles (VMATs). Using kinase inhibitors we also showed that E₂-mediated dopamine efflux is dependent on protein kinase C and MEK activation, but not on PI3K or protein kinase A. In plasma membrane there are ligand-independent associations of ERα and ERβ (but not GPR30) with DAT. Conditions which cause efflux (a 9 min 10^-9M E₂treatment) cause trafficking of ERα (stimulatory) to the plasma membrane and trafficking of ERβ (inhibitory) away from the plasma membrane. In contrast, E₁and E₃can inhibit efflux with a nonmonotonic dose pattern, and cause DAT to leave the plasma membrane.</p> <p>Conclusion</p> <p>Such mechanisms explain how gender biases in some DAT-dependent diseases can occur.</p

Eccentric resistance training and beta-hydroxy-beta-methylbutyrate free acid affects muscle PGC-1 alpha expression and serum irisin, nesfatin-1 and resistin in rats

The hypothalamus controls metabolism and feeding behaviour via several signals with other tissues. Exercise and supplements can change hypothalamic signalling pathways, so the present study investigated the influence of eccentric resistance training and β-hydroxy-β-methylbutyrate free acid supplementation on PGC-1α expression, serum irisin, nesfatin-1 and resistin concentrations. Thirty-two male rats (8 weeks old, 200±17 g body mass) were randomly allocated to control, β-hydroxy-β-methylbutyrate free acid supplementation (HMB), eccentric resistance training (ERT), and β-hydroxy-β-methylbutyrate free acid supplementation plus eccentric resistance training (HMB+ERT) groups. Training groups undertook eccentric resistance training (6 weeks, 3 times a week) and supplement groups consumed β-hydroxy-β-methylbutyrate free acid (HMB-FA) orally (76 mg kg-1 day-1). Twenty-four hours after the last training session, serum and triceps brachii muscle samples were collected and sent to the laboratory for analysis. Two-way ANOVA and Pearson correlation were employed (significance level: P<0.05). The results showed that eccentric resistance training increases skeletal muscle PGC-1α gene expression, as well as serum levels of irisin and nesfatin-1 (P=0.001). Eccentric resistance training decreased the serum concentration of resistin (P=0.001). HMB-FA supplementation increased skeletal muscle PGC-1α gene expression (P=0.002), as well as the serum concentration of irisin and nesfatin-1 (P=0.001), but decreased the serum concentration of resistin (P=0.001). Significant correlations were observed between PGC-1α gene expression and serum concentrations of irisin, nesfatin-1 and resistin. HMB-FA supplementation with eccentric resistance training may induce crosstalk between peptide release from other tissues and increases maximal muscle strength. The combination of the two interventions had a more substantial effect than each in isolation

Climatically sensitive transfer of iron to maritime Antarctic ecosystems by surface runoff

Iron supplied by glacial weathering results in pronounced hotspots of biological production in an otherwise iron-limited Southern Ocean Ecosystem. However, glacial iron inputs are thought to be dominated by icebergs. Here we show that surface runoff from three island groups of the maritime Antarctic exports more filterable (<0.45 μm) iron (6–81 kg km−2 a−1) than icebergs (0.0–1.2 kg km−2 a−1). Glacier-fed streams also export more acid-soluble iron (27.0–18,500 kg km−2 a−1) associated with suspended sediment than icebergs (0–241 kg km−2 a−1). Significant fluxes of filterable and sediment-derived iron (1–10 Gg a−1 and 100–1,000 Gg a−1, respectively) are therefore likely to be delivered by runoff from the Antarctic continent. Although estuarine removal processes will greatly reduce their availability to coastal ecosystems, our results clearly indicate that riverine iron fluxes need to be accounted for as the volume of Antarctic melt increases in response to 21st century climate change