Vortex Formation and Foraging in Polyphenic Spadefoot Toad Tadpoles

Cryptic genetic variation in brain gene expression precedes the evolution of cannibalism in spadefoot toad tadpoles

The origins of novel behaviors are poorly understood, despite behavior's hypothesized roles in evolution. One model, "genetic accommodation," proposes that selection on ancestral phenotypic plasticity may precede the evolution of novel traits. A critical assumption of genetic accommodation is that ancestral lineages possess heritable genetic variation for trait plasticity that is revealed in novel environments, thereby providing the raw materials for subsequent refinement of the novel trait in derived lineages. Here, we use a combination of behavioral and RNA-seq approaches to test this assumption in the context of a novel tadpole behavior: predatory cannibalism. Cannibalism evolved in the spadefoot genus Spea, where an invertebrate diet induces a carnivorous tadpole morph capable of consuming live conspecific tadpoles. In contrast, closely related Scaphiopus tadpoles do not induce this carnivorous phenotype. Through species comparisons, we found that ancestral Spea likely expressed behavioral plasticity and harbored latent (i.e., "cryptic") genetic variation in brain gene expression plasticity associated with cannibalism-inducing cues. Further, we found that this cryptic genetic variation includes genes specifically associated with a dietary response and cannibalism in derived Spea. Our results suggest that novel behaviors, alongside novel morphologies, can evolve via the process of genetic accommodation. More generally, our results provide key evidence for the plausibility of genetic accommodation, revealing that cryptic genetic variation-the raw material for the evolution of novel traits-exists in natural populations at the level of gene expression.

Spontaneous stable rotation of flocking flexible active matter

In this paper we present an n-node flexible active matter model to study the collective motion due to the flocking of individual achiral agents on a two-dimensional surface. By introducing a measure of the direction detectability of the agents to tune their body direction towards the food source, we find that a spontaneous stable cluster rotation emerges with increasing direction detectability. The spontaneous rotation is synchronized with the chirality produced by the alignment of their bodies under the impetus of the active force. A linear relationship between the normalized angular velocity and chirality is observed and the numerical simulation agrees well with the analytical derivation. The conclusions explain well the spontaneous stable rotation of clusters that exists in many flexible active matter systems, like worms or dogs, when they flock to the same single source.

Relative telencephalon size does not affect collective motion in the guppy (Poecilia reticulata)

Collective motion is common across all animal taxa, from swarming insects to schools of fish. The collective motion requires intricate behavioral integration among individuals, yet little is known about how evolutionary changes in brain morphology influence the ability for individuals to coordinate behavior in groups. In this study, we utilized guppies that were selectively bred for relative telencephalon size, an aspect of brain morphology that is normally associated with advanced cognitive functions, to examine its role in collective motion using an open-field assay. We analyzed high-resolution tracking data of same-sex shoals consisting of 8 individuals to assess different aspects of collective motion, such as alignment, attraction to nearby shoal members, and swimming speed. Our findings indicate that variation in collective motion in guppy shoals might not be strongly affected by variation in relative telencephalon size. Our study suggests that group dynamics in collectively moving animals are likely not driven by advanced cognitive functions but rather by fundamental cognitive processes stemming from relatively simple rules among neighboring individuals.

A Circular Formation Method for Biomimetic Robotic Fish Inspired by Fish Milling

Circular motion phenomena, akin to fish milling, are prevalent within the animal kingdom. This paper delineates two fundamental mechanisms underlying such occurrences: forward following and circular topological communication. Leveraging these pivotal concepts, we present a multi-agent formation circular model based on a second-order integrator. This model engenders the attainment of homogeneous intelligence convergence along the circumferential trajectory. The convergence characteristics are intricately linked to the number of agents and the model parameters. Consequently, we propose positive and negative solutions for ascertaining the convergent circle property and model parameters. Furthermore, by integrating our proposed formation control methodology with a robotic fish dynamics model, we have successfully implemented simulations and experiments, demonstrating the circular formation of multiple biomimetic robotic fish. This study provides a mathematical explication for the circular motion observed in animal groups and introduces a novel approach to achieving circular formation in multiple robots inspired by biological phenomena.

Collective dynamics of dipolar self-propelled particles

We present a numerical study of the collective behavior of self-propelled particles for which dipolar interactions are considered. These are obtained by introducing pointlike magnetic dipoles in the particles. Various dynamical regimes are found depending on three major parameters: the density of particles, the ratio Γ defined as the competition between kinetic energy and potential magnetic energy, as well as the orientation of the magnetic dipoles inherent to the particles. Patterns such as chains, vortices, flocks, and strips have been obtained.

Social Synchronization of Conditioned Fear in Mice Requires Ventral Hippocampus Input to the Amygdala

BACKGROUND

Social organisms synchronize behaviors as an evolutionary-conserved means of thriving. Synchronization under threat, in particular, benefits survival and occurs across species, including humans, but the underlying mechanisms remain unknown because of the scarcity of relevant animal models. Here, we developed a rodent paradigm in which mice synchronized a classically conditioned fear response and identified an underlying neuronal circuit.

METHODS

Male and female mice were trained individually using auditory fear conditioning and then tested 24 hours later as dyads while allowing unrestricted social interaction during exposure to the conditioned stimulus under visible or infrared illumination to eliminate visual cues. The synchronization of the immobility or freezing bouts was quantified by calculating the effect size Cohen's d for the difference between the actual freezing time overlap and the overlap by chance. The inactivation of the dorsomedial prefrontal cortex, dorsal hippocampus, or ventral hippocampus was achieved by local infusions of muscimol. The chemogenetic disconnection of the hippocampus-amygdala pathway was performed by expressing hM4D(Gi) in the ventral hippocampal neurons and infusing clozapine N-oxide in the amygdala.

RESULTS

Mice synchronized cued but not contextual fear. It was higher in males than in females and attenuated in the absence of visible light. Inactivation of the ventral but not dorsal hippocampus or dorsomedial prefrontal cortex abolished fear synchronization. Finally, the disconnection of the hippocampus-amygdala pathway diminished fear synchronization.

CONCLUSIONS

Mice synchronize expression of conditioned fear relying on the ventral hippocampus-amygdala pathway, suggesting that the hippocampus transmits social information to the amygdala to synchronize threat response.

A fellow-following-principle based group model and its application to fish school analysis

Group models based on simple rules are viewed as a bridge to clarifying animal group movements. The more similar a model to real-world observations, the closer it is to the essence of such movements. Inspired by the fish school, this study suggests a principle called fellow-following for group movements. More specifically, a simple-rules-based model was proposed and extended into a set of concrete rules, and two- and three-dimensional group models were established. The model results are intuitively similar to the fish school, and when the group size increases, the milling phase of both the model and fish school tends from unstable to stable. Further, we proposed a novel order parameter and a similarity measurement framework for group structures. The proposed model indicates the intuition similarity, consistency of dynamic characteristics, and static structure similarity with fish schools, which suggests that the principle of fellow-following may reveal the essence of fish school movements. Our work suggests a different approach for the self-organized formation of a swarm robotic system based on local information.

Feeding exposure and feeding behaviour as relevant approaches in the assessment of the effects of micro(nano)plastics to early life stages of amphibians

The sedimentation of micro and nanosized plastics is of considerable environmental relevance and the need to assess its sublethal effects to biota increasingly recognized. In their majority, as bottom, non-selective grazers, independent-feeding young life stages of amphibians, an already severely endangered worldwide group, may be particularly vulnerable to sedimented plastics. Alongside, they may be good model organisms for the assessment of the effects of micro(nano)plastics (MNPs) through ingestion. However, to our knowledge, few studies have assessed amphibians' exposure to MNPs through contaminated food or its effects in feeding behaviour assays. The available studies reveal a lack of consistent methodology: organisms, food type, media of exposure, or exposure conditions (temperature and light) in the assessment of effects. This perspective article, will address major differences found in the available studies, identifying type, size and concentrations of the polymers tested, species, and observed effects, aiming to highlight the importance of feeding exposure assays when attempting to evaluate the effect of MNPs in amphibians.

Individualism versus collective movement during travel

Collective movement may emerge if coordinating one’s movement with others produces a greater benefit to oneself than can be achieved alone. Experimentally, the capacity to manoeuvre simulated groups in the wild could enable powerful tests of the impact of collective movement on individual decisions. Yet such experiments are currently lacking due to the inherent difficulty of controlling whole collectives. Here we used a novel technique of experimentally simulating the movement of collectives of social hermit crabs (Coenobita compressus) in the wild. Using large architectural arrays of shells dragged across the beach, we generated synchronous collective movement and systematically varied the simulated collective’s travel direction as well as the context (i.e., danger level). With drone video from above, we then tested whether focal individuals were biased in their movement by the collective. We found that, despite considerable engagement with the collective, individuals’ direction was not significantly biased. Instead, individuals expressed substantial variability across all stimulus directions and contexts. Notably, individuals typically achieved shorter displacements in the presence of the collective versus in the presence of the control stimulus, suggesting an impact of traffic. The absence of a directional bias in individual movement due to the collective suggests that social hermit crabs are individualists, which move with a high level of opportunistic independence, likely thanks to the personal architecture and armour they carry in the form of a protective shell. Future studies can manipulate this level of armour to test its role in autonomy of movement, including the consequences of shell architecture for social decisions. Our novel experimental approach can be used to ask many further questions about how and why collective and individual movement interact.

Testing a thermodynamic approach to collective animal behavior in laboratory fish schools

Collective behaviors displayed by groups of social animals are observed frequently in nature. Understanding and predicting the behavior of complex biological systems is dependent on developing effective descriptions and models. While collective animal systems are characteristically nonequilibrium, we can employ concepts from equilibrium statistical mechanics to motivate the measurement of material-like properties in laboratory animal aggregates. Here, we present results from a new set of experiments that utilize high speed footage of two-dimensional schooling events, particle tracking, and projected static and dynamic light fields to observe and control the behavior of negatively phototaxic fish schools (Hemigrammus bleheri). First, we use static light fields consisting of dark circular regions to produce visual stimuli that confine the schools to a range of areas. We find that schools have a maximum density which is independent of group size, and that a swim pressurelike quantity, Π increases linearly with number density, suggesting that unperturbed schools exist on an isotherm. Next, we use dynamic light fields where the radius of the dark region shrinks linearly with time to compress the schools. We find that an effective temperature parameter depends on the compression time and our results are thus consistent with the school having a constant heat flux. These findings further evidence the utility of effective thermodynamic descriptions of nonequilibrium systems in collective animal behavior.

Collective gradient sensing in fish schools

Throughout the animal kingdom, animals frequently benefit from living in groups. Models of collective behaviour show that simple local interactions are sufficient to generate group morphologies found in nature (swarms, flocks and mills). However, individuals also interact with the complex noisy environment in which they live. In this work, we experimentally investigate the group performance in navigating a noisy light gradient of two unrelated freshwater species: golden shiners (Notemigonuscrysoleucas) and rummy nose tetra (Hemigrammus bleheri). We find that tetras outperform shiners due to their innate individual ability to sense the environmental gradient. Using numerical simulations, we examine how group performance depends on the relative weight of social and environmental information. Our results highlight the importance of balancing of social and environmental information to promote optimal group morphologies and performance.

Brain size does not impact shoaling dynamics in unfamiliar groups of guppies (Poecilia reticulata)

Collective movement is achieved when individuals adopt local rules to interact with their neighbours. How the brain processes information about neighbours' positions and movements may affect how individuals interact in groups. As brain size can determine such information processing it should impact collective animal movement. Here we investigate whether brain size affects the structure and organisation of newly forming fish shoals by quantifying the collective movement of guppies (Poecilia reticulata) from large- and small-brained selection lines, with known differences in learning and memory. We used automated tracking software to determine shoaling behaviour of single-sex groups of eight or two fish and found no evidence that brain size affected the speed, group size, or spatial and directional organisation of fish shoals. Our results suggest that brain size does not play an important role in how fish interact with each other in these types of moving groups of unfamiliar individuals. Based on these results, we propose that shoal dynamics are likely to be governed by relatively basic cognitive processes that do not differ in these brain size selected lines of guppies.

Does relatedness influence the intensity of competition in Bufo gargarizans minshanicus tadpoles?

Kin selection theory predicts that mechanisms should evolve to reduce kin competition when this maximizes inclusive fitness. In this study, we tested these predictions by investigating the effects of relatedness on fitness-related metamorphic traits (e.g., length of larval period, size at metamorphosis, body condition and survival rate). We did this in a laboratory experiment by exposing individuals of Bufo gargarizans minshanicus to competition with full-sibling or non-sibling larvae. Although tadpoles seemed to grow slightly better in environments when their competition consisted of full-siblings than when their competitors consisted of non-siblings, these effects of relatedness on the growth and development were not significant. Therefore, we suggest that interference competition may be equally intense in in full-sibling and non-sibling groups.

Social behaviour and collective motion in plant-animal worms

Social behaviour may enable organisms to occupy ecological niches that would otherwise be unavailable to them. Here, we test this major evolutionary principle by demonstrating self-organizing social behaviour in the plant-animal, Symsagittifera roscoffensis. These marine aceol flat worms rely for all of their nutrition on the algae within their bodies: hence their common name. We show that individual worms interact with one another to coordinate their movements so that even at low densities they begin to swim in small polarized groups and at increasing densities such flotillas turn into circular mills. We use computer simulations to: (i) determine if real worms interact socially by comparing them with virtual worms that do not interact and (ii) show that the social phase transitions of the real worms can occur based only on local interactions between and among them. We hypothesize that such social behaviour helps the worms to form the dense biofilms or mats observed on certain sun-exposed sandy beaches in the upper intertidal of the East Atlantic and to become in effect a super-organismic seaweed in a habitat where macro-algal seaweeds cannot anchor themselves. Symsagittifera roscoffensis, a model organism in many other areas in biology (including stem cell regeneration), also seems to be an ideal model for understanding how individual behaviours can lead, through collective movement, to social assemblages.

Understanding how animal groups achieve coordinated movement

Moving animal groups display remarkable feats of coordination. This coordination is largely achieved when individuals adjust their movement in response to their neighbours' movements and positions. Recent advancements in automated tracking technologies, including computer vision and GPS, now allow researchers to gather large amounts of data on the movements and positions of individuals in groups. Furthermore, analytical techniques from fields such as statistical physics now allow us to identify the precise interaction rules used by animals on the move. These interaction rules differ not only between species, but also between individuals in the same group. These differences have wide-ranging implications, affecting how groups make collective decisions and driving the evolution of collective motion. Here, I describe how trajectory data can be used to infer how animals interact in moving groups. I give examples of the similarities and differences in the spatial and directional organisations of animal groups between species, and discuss the rules that animals use to achieve this organisation. I then explore how groups of the same species can exhibit different structures, and ask whether this results from individuals adapting their interaction rules. I then examine how the interaction rules between individuals in the same groups can also differ, and discuss how this can affect ecological and evolutionary processes. Finally, I suggest areas of future research.

COLLECTIVE VORTEX BEHAVIORS: DIVERSITY, PROXIMATE, AND ULTIMATE CAUSES OF CIRCULAR ANIMAL GROUP MOVEMENTS

Ant mill, caterpillar circle, bat doughnut, amphibian vortex, duck swirl, and fish torus are different names for rotating circular animal formations, where individuals turn around a common center. These "collective vortex behaviors" occur at different group sizes from pairs to several million individuals and have been reported in a large number of organisms, from bacteria to vertebrates, including humans. However, to date, no comprehensive review and synthesis of the literature on vortex behaviors has been conducted. Here, we review the state of the art of the proximate and ultimate causes of vortex behaviors. The ubiquity of this behavioral phenomenon could suggest common causes or fundamental underlying principles across contexts. However, we find that a variety of proximate mechanisms give rise to vortex behaviors. We highlight the potential benefits of collective vortex behaviors to individuals involved in them. For example, in some species, vortices increase feeding efficiency and could give protection against predators. It has also been argued that vortices could improve collective decision-making and information transfer. We highlight gaps in our understanding of these ubiquitous behavioral phenomena and discuss future directions for research in vortex studies.

Evolution of rapid development in spadefoot toads is unrelated to arid environments

The extent to which species' life histories evolve to match climatic conditions is a critical question in evolutionary biology and ecology and as human activities rapidly modify global climate. GIS-based climatic data offer new opportunities to rigorously test this question. Superficially, the spadefoot toads of North America (Scaphiopodidae) seem to offer a classic example of adaptive life-history evolution: some species occur in extremely dry deserts and have evolved the shortest aquatic larval periods known among anurans. However, the relationships between the climatic conditions where spadefoots occur and the relevant life-history traits have not been explicitly tested. Here, we analyzed these relationships using GIS-based climatic data, published life-history data, and a time-calibrated phylogeny for pelobatoid frogs. Surprisingly, we find no significant relationships between life-history variables and precipitation or aridity levels where these species occur. Instead, rapid development in pelobatoids is strongly related to their small genome sizes and to phylogeny.

Individual-to-resource landscape interaction strength can explain different collective feeding behaviours

Taking in sufficient quantities of nutrients is vital for all living beings and in doing so, individuals interact with the local resource environment. Here, we focus explicitly on the interactions between feeding individuals and the resource landscape. In particular, we are interested in the emergent movement dynamics resulting from these interactions. We present an individual-based simulation model for the movement of populations in a resource landscape that allows us to vary the strength of the interactions mentioned above. The key assumption and novelty of our model is that individuals can cause the release of additional nutrients, as well as consuming them. Our model produces clear predictions. For example, we expect more tortuous individual movement paths and higher levels of aggregation in populations occupying homogeneous environments where individual movement makes more nutrients available. We also show how observed movement dynamics could change when local nutrient sources are depleted or when the population density increases. Our predictions are testable and qualitatively reproduce the different feeding behaviours observed in filter-feeding ducks, for example. We suggest that considering two-way interactions between feeding individuals and resource landscapes could help to explain fine-scale movement dynamics.

Collective motion of humans in mosh and circle pits at heavy metal concerts

Human collective behavior can vary from calm to panicked depending on social context. Using videos publicly available online, we study the highly energized collective motion of attendees at heavy metal concerts. We find these extreme social gatherings generate similarly extreme behaviors: a disordered gaslike state called a mosh pit and an ordered vortexlike state called a circle pit. Both phenomena are reproduced in flocking simulations demonstrating that human collective behavior is consistent with the predictions of simplified models.

Making friends: social attraction in larval green and golden bell frogs, Litoria aurea

Socio-ecological models combine environmental and social factors to explain the formation of animal groups. In anurans, tadpole aggregations have been reported in numerous species, but the factors driving this behaviour remain unclear. We conducted controlled choice experiments in the lab to determine whether green and golden bell frog (Litoria aurea) tadpoles are directly attracted to conspecifics (social factors) in the absence of environmental cues. Using repeated measures, we found that individual tadpoles strongly preferred associating with conspecifics compared to being alone. Furthermore, this preference was body size dependent, and associating tadpoles were significantly smaller than non-associating tadpoles. We suggest that small tadpoles are more vulnerable to predation and therefore more likely to form aggregations as an anti-predator behaviour. We demonstrate that tadpoles present an ideal model system for investigating how social and ecological factors influence group formation in vertebrates.