Selective social interactions and speed-induced leadership in schooling fish.

Animals moving together in groups are believed to interact among each other with effective social forces, such as attraction, repulsion, and alignment. Such forces can be inferred using "force maps," i.e., by analyzing the dependency of the acceleration of a focal individual on relevant variables. Here, we introduce a force map technique suitable for the analysis of the alignment forces experienced by individuals. After validating it using an agent-based model, we apply the force map to experimental data of schooling fish. We observe signatures of an effective alignment force with faster neighbors and an unexpected antialignment with slower neighbors. Instead of an explicit antialignment behavior, we suggest that the observed pattern is the result of a selective attention mechanism, where fish pay less attention to slower neighbors. This mechanism implies the existence of temporal leadership interactions based on relative speeds between neighbors. We present support for this hypothesis both from agent-based modeling as well as from exploring leader-follower relationships in the experimental data.

Motion leadership and local interaction in two species of freshwater fish (Danio rerio and Hyphessobrycon herbertaxelrodi).

The authors studied momentary motion leadership in small groups of black neon tetra (Hyphessobrycon herbertaxelrodi) and zebrafish (Danio rerio), its relationship with local interaction parameters, such as the acceleration and turning angle of the individuals, and the relative locations of the individuals within the group. The purpose was to know whether leadership tended to be monopolised by certain individuals or whether it was equitably shared between them and if there were differences in leadership sharing between these two species, which are known to have different degrees of cohesion and polarisation. The authors filmed groups of two, three, four and eight fishes of each species and tracked their individual motion by image analysis and trajectory extraction. In both species, motion leadership was not monopolized but egalitarian and very short lived, with leadership shifts distributed randomly over time. The duration of leadership episodes decreased as group size increased and was longer in black neon tetra than in zebrafish. Momentary leaders did not tend to be in the front positions, but closer to the centre of the group. Acceleration and turning angle were more extreme in zebrafish than in black neon tetra and in the momentary leaders than the followers in both species. In general, these differences between species and between leaders/followers were qualitatively similar with some differences in detail, indicating that the relationship between motion leadership and local interaction parameters is likely to conform to a general physical law.

Previous Experience Seems Crucial to Eliminate the Sex Gap in Geometry Learning When Solving a Navigation Task in Rats (Rattus norvegicus).

There is much evidence, both in humans and rodents, that while navigating males tend to use geometric information whereas females rely more on landmarks. The present work attempts to alter the geometry bias in female rats. In Experiment 1 three groups of female rats were trained in a triangular-shaped pool to find a hidden platform, whose location was defined in terms of two sources of information, a landmark outside the pool and a particular corner of the pool. On a subsequent test trial with the triangular pool and no landmark, females with prior experience with two other pool shapes-with a kite-shaped pool and with a rectangular-shaped pool (Group Long Previous Experience, LPE), were significantly more accurate than control rats without such prior experience (Group No Previous Experience, NPE). Rats with a short previous experience-with the rectangular-shaped pool only (Group Short Previous Experience, SPE) did not differ from Group NPE. These results suggest that the previous experience with different shaped-pools could counteract the geometry bias in female rats. Then, Experiment 2A directly compared the performance of LPE males and females of Experiment 1, although conducting several test trials (i.e., shape, landmark, and preference). The differences between males and females disappeared in the three tests. Moreover, in a final test trial both males and females could identify the correct corner in an incomplete pool by its local, instead of global, properties. Finally, Experiment 2B compared the performance of NPE rats, males and females, of Experiment 1. On the test trial with the triangular pool and no landmark, males were significantly more accurate than females. The results are explained in the framework of selective attention.

Local interaction rules and collective motion in black neon tetra (Hyphessobrycon herbertaxelrodi) and zebrafish (Danio rerio).

We explored the local motion rules used by interacting individuals in small groups of black neon tetra (Hyphessobrycon herbertaxelrodi) and zebrafish (Danio rerio) to ascertain if and how these rules underlie the fishes' global collective coordinated motion. As these 2 species show very different styles of collective motion in terms of cohesion and polarization, we expected to find differences in their individual behavioral rules. We recorded groups of 2, 3, 4, and 8 fish of each species; tracked their individual trajectories; and studied how their individual turning angles and accelerations varied as a function of heading differences, distances, and relative angles to their neighbors. We found that black neon tetra and zebrafish differed in terms of their preferential positions with respect to their neighbors, the magnitude of turning angles and accelerations, and the way these angles and accelerations are modulated by both the distance from neighbors (thus suggesting a "repulsion" zone in black neon tetra but not in zebrafish) and the heading difference and relative angle to neighbors. Our results enable us to infer that, in black neon tetra, avoiding excessive proximity and collision takes priority over cohesion, and cohesion takes priority over polarization. This provides evidence that rules are similar in species of very different genera and that differences are a matter of degree. Our results also provide substantial empirical evidence to support the theoretical assumptions made in agent-based models that simulate coordinated collective motion in many different animal species. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Differences in shoaling behavior in two species of freshwater fish (Danio rerio and Hyphessobrycon herbertaxelrodi).

Fish can gain significant adaptive advantages when living in a group and they exhibit a wide variety of types of collective motion. The scientific literature recognizes 2 main patterns: shoals (aggregations of individuals that remain close to each other), and schools (aggregations of aligned, or polarized, individuals). We analyzed the collective motion of 2 social fish species, zebrafish (Danio rerio) and black neon tetra (Hyphessobrycon herbertaxelrodi), and compared their patterns of movement and the effect of group size and environmental constraints such as water column height and tank geometry on the collective motion of both species. We recorded the movement of groups of fish (n = 10 and n = 20) using 2 tank geometries: a rectangular shape and a rectangular shape with rounded corners; and we also manipulated the water column height (15 and 25 cm). We extracted the individual fish trajectories and calculated indices of cohesion, coordination, group density and group shape. The results showed that the 2 species had different types of collective motion: the zebrafish's global motion matched that of a shoal, while the black neon tetra's motion matched that of a school. Indirect evidence indicated that the 2 species tended to occupy the vertical space differently while swimming in a group. Finally, we found that tank geometry did not affect group polarization, whereas group size had an effect on black neon tetra density, which was higher in small group sizes than in large ones. (PsycINFO Database Record

Modelling the emergence of coordinated collective motion by minimizing dissatisfaction.

Coordinated collective motion (CCM) has been recently studied using agent-based simulations by applying three behavioural rules: repulsion, attraction and alignment. But these rules are so similar to the expected group behaviour that it can hardly be labelled emergent. We developed an agent-based model that produces CCM using a set of low-level dyadic interaction rules. The agents change their positions with regard to other agents in order to minimize their own dissatisfaction with their inter-individual distances. To test the emergence of CCM, several simulation experiments were performed. The results show that the agents were able to achieve CCM after a few thousand time steps, and that the bigger the area perceived by them, the more coordinated and cohesive the group motion became. An increased memory span and capacity to remember other agents' identities improved cohesion and coordination. The relationship with biological referents is discussed.

A method for resolving occlusions when multitracking individuals in a shoal.

Studying the collective behavior of fishes often requires tracking a great number of individuals. When many fishes move together, it is common for individuals to move so close to each other that some fishes superimpose themselves on others during one or several units of time, which impacts on tracking accuracy (i.e., loss of fish trajectories, interchange of fish identities). Type 1 occlusions arise when two fishes swim so near each other that they look like one long fish, whereas type 2 occlusions occur when the fishes' trajectories cross to create a T- or X-shaped individual. We propose an image processing method for resolving these types of occlusions when multitracking shoals in two dimensions. We assessed processing effectiveness after videorecording shoals of 20 and 40 individuals of two species that exhibit different shoal styles: zebrafish (Danio rerio) and black neon tetras (Hyphessobrycon herbertaxelrodi). Results show that, although the number of occlusions depended on both the number of individuals and the species, the method is able to effectively resolve a great deal of occlusions, irrespective of the species and the number of individuals. It also produces images that can be used in a multitracking system to detect individual fish trajectories. Compared to other methods, our approach makes it possible to study shoals with water depths similar to those seen in the natural conditions of the two species studied.

Navigation with two landmarks in rats (Rattus norvegicus): the role of landmark salience.

In two experiments, male and female rats were trained in a Morris pool in the presence of 1 (Experiment 1) or 2 (Experiment 2) landmarks, which were placed relatively close in relation to a hidden platform. Experiment 1 established the relative salience of 3 landmarks. Two of them revealed a similar salience, and smaller than a third one, the most salient landmark, both in training and on a test trial without the platform. Then in Experiment 2 rats were extensively trained to find a hidden platform in the presence of a configuration formed by 2 landmarks and the effects of varying the salience of one of the landmarks were studied. Subsequent test trials without the platform revealed that finding the platform was controlled by different strategies and that the rats were taking advantage of this redundancy depending on the nature of the test trials. Surprisingly, in Experiment 2 a clear sex difference was found on escape trials only, with males reaching the platform faster than females.