Collective predator evasion: Putting the criticality hypothesis to the test

According to the criticality hypothesis, collective biological systems should operate in a special parameter region, close to so-called critical points, where the collective behavior undergoes a qualitative change between different dynamical regimes. Critical systems exhibit unique properties, which may benefit collective information processing such as maximal responsiveness to external stimuli. Besides neuronal and gene-regulatory networks, recent empirical data suggests that also animal collectives may be examples of self-organized critical systems. However, open questions about self-organization mechanisms in animal groups remain: Evolutionary adaptation towards a group-level optimum (group-level selection), implicitly assumed in the "criticality hypothesis", appears in general not reasonable for fission-fusion groups composed of non-related individuals. Furthermore, previous theoretical work relies on non-spatial models, which ignore potentially important self-organization and spatial sorting effects. Using a generic, spatially-explicit model of schooling prey being attacked by a predator, we show first that schools operating at criticality perform best. However, this is not due to optimal response of the prey to the predator, as suggested by the "criticality hypothesis", but rather due to the spatial structure of the prey school at criticality. Secondly, by investigating individual-level evolution, we show that strong spatial self-sorting effects at the critical point lead to strong selection gradients, and make it an evolutionary unstable state. Our results demonstrate the decisive role of spatio-temporal phenomena in collective behavior, and that individual-level selection is in general not a viable mechanism for self-tuning of unrelated animal groups towards criticality

Evolutionary Impact of Size-Selective Harvesting on Shoaling Behavior: Individual-Level Mechanisms and Possible Consequences for Natural and Fishing Mortality

16 pages, 5 figures, 1 table, supplementary data https://doi.org/10.5061/dryad.x95x69pkf; supplementary material https://www.journals.uchicago.edu/doi/suppl/10.1086/718591.-- Data and Code Availability: Experimental data and the R code have been deposited in the Dryad Digital Repository (https://doi.org/10.5061/dryad.x95x69pkf; Sbragaglia 2021). The code to run the burst-and-coast model with the fishing/predator scenarios is available at GitHub (https://doi.org/10.5281/zenodo.5651937; https://github.com/PaPeK/sde_burst_coast). The optimization was done with a Python implementation of the CMA-ES (https://github.com/CMA-ES/pycma)Intensive and size-selective harvesting is an evolutionary driver of life history as well as individual behavioral traits. Yet whether and to what degree harvesting modifies the collective behavior of exploited species are largely unknown. We present a multigeneration harvest selection experiment with zebrafish, Danio rerio, as a model species to understand the effects of size-selective harvesting on shoaling behavior. The experimental system is based on a large-harvested (typical of most wild-capture fisheries targeting larger size classes) and small-harvested (typical of specialized fisheries and gape-limited predators targeting smaller size classes) selection lines. By combining high-resolution tracking of fish behavior with computational agent-based modeling, we show that shoal cohesion changed in the direction expected by a trade-off between individual vigilance and the use of social cues. In particular, we document a decrease of individual vigilance in the small-harvested line, which was linked to an increase in the attention to social cues, favoring more cohesive shoals. Opposing outcomes were found for the large-harvested line, which formed less cohesive shoals. Using the agent-based model, we outline possible consequences of changes in shoaling behavior for both fishing and natural mortality. The changes in shoaling induced by large size-selective harvesting may decrease fishing mortality but increase mortality by natural predators. Our work suggests an insofar overlooked evolutionary mechanism by which size-selective harvesting can affect fishing and natural mortality of exploited fishV.S. was supported by a Leibniz-DAAD (German Academic Exchange Service) postdoctoral research fellowship (91632699), and he is now supported by the Spanish Ministry of Science and Innovation (Juan de la Cierva Incorporación Research Fellowship, IJC2018-035389-I). V.S. also acknowledges the Spanish government through the Severo Ochoa Centre of Excellence accreditation to the Department of Marine Renewable Resources, Institute of Marine Sciences (ICM-CSIC; CEX2019-000928-S). P.P.K. and P.R. received financial support from the German Research Foundation (DFG) under RO 4766/2-1 and under Germany’s Excellence Strategy (EXC 2002/1 Science of Intelligence, project 390523135)Peer reviewe

Inferring country-specific import risk of diseases from the world air transportation network

Disease propagation between countries strongly depends on their effective distance, a measure derived from the world air transportation network (WAN). It reduces the complex spreading patterns of a pandemic to a wave-like propagation from the outbreak country, establishing a linear relationship to the arrival time of the unmitigated spread of a disease. However, in the early stages of an outbreak, what concerns decision-makers in countries is understanding the relative risk of active cases arriving in their country-essentially, the likelihood that an active case boarding an airplane at the outbreak location will reach them. While there are data-fitted models available to estimate these risks, accurate mechanistic, parameter-free models are still lacking. Therefore, we introduce the 'import risk' model in this study, which defines import probabilities using the effective-distance framework. The model assumes that airline passengers are distributed along the shortest path tree that starts at the outbreak's origin. In combination with a random walk, we account for all possible paths, thus inferring predominant connecting flights. Our model outperforms other mobility models, such as the radiation and gravity model with varying distance types, and it improves further if additional geographic information is included. The import risk model's precision increases for countries with stronger connections within the WAN, and it reveals a geographic distance dependence that implies a pull- rather than a push-dynamic in the distribution process.</p

Magnetoelastic resonance as a probe for exchange springs at antiferromagnet ferromagnet interfaces

In prototype ferromagnet antiferromagnet interfaces we demonstrate that surface acoustic waves can be used to identify complex magnetic phases arising upon evolution of exchange springs in an applied. Applying sub GHz surface acoustic waves to study the domain structure of the ferromagnetic layer in exchange biased bilayers of Ir20Mn80 Co60Fe20B20, we are able to associate the magnetoelastic resonance with the presence of the exchange spin spirals in both the ferromagnetic and antiferromagnetic layer. Our findings offer a complementary, integrative insight into emergent magnetic materials for applications of noncollinear spin textures in view of low energy consumption spintronic device

Rank and relative performance of import risk estimation models.

The different import probability models are compared via their rank (A) and relative performance (B), with the highest values representing the best approach. The rank and relative performance are shown for each (black dots) of the six comparison measures (corr, logcorr, RMSE, logRMSE, cpc, τKendall) the box illustrates the interquartile range, the horizontal line the median and the red triangle the mean. The colors of the boxes illustrate the different distance measures in use. The outlier measure of the import risk models (I.R.) is the logRMSE, where the gravity models with effective distance are performing best. See Material and methods for definitions of comparison measures and Figs E, F in S1 Text for absolute and detailed relative performance.</p

Dataset associated with "Magnetoelastic resonance as a probe for exchange springs at antiferromagnet-ferromagnet interfaces"

Dataset associated with "Magnetoelastic resonance as a probe for exchange springs at antiferromagnet-ferromagnet interfaces" by K. M. Seemann et al

Source countries’ prediction quality and WAN outflow.

The correlation between the logarithm of the import risk and the reference import probability improves with the outflow of the respective source country (top). Examples of source countries with particularly low (ER, Eritrea) and high (GB, Great Britain) outflow and log_corr are shown with their import risk and reference import risk to target countries (middle row). Countries with exceptionally low log_corr measures compared to source countries with a comparable outflow are either historically linked to specific regions as Australia (AU) and Israel (IL) to European countries (lower right panel) or politically as Macao (MO) as a special administrative region of China.</p