Asymmetry in pay-off predicts how familiar individuals respond to one another

Rhythm of relationships in a social fish over the course of a full year in the wild

BACKGROUND

Animals are expected to adjust their social behaviour to cope with challenges in their environment. Therefore, for fish populations in temperate regions with seasonal and daily environmental oscillations, characteristic rhythms of social relationships should be pronounced. To date, most research concerning fish social networks and biorhythms has occurred in artificial laboratory environments or over confined temporal scales of days to weeks. Little is known about the social networks of wild, freely roaming fish, including how seasonal and diurnal rhythms modulate social networks over the course of a full year. The advent of high-resolution acoustic telemetry enables us to quantify detailed social interactions in the wild over time-scales sufficient to examine seasonal rhythms at whole-ecosystems scales. Our objective was to explore the rhythms of social interactions in a social fish population at various time-scales over one full year in the wild by examining high-resolution snapshots of a dynamic social network.

METHODS

To that end, we tracked the behaviour of 36 adult common carp, Cyprinus carpio, in a 25 ha lake and constructed temporal social networks among individuals across various time-scales, where social interactions were defined by proximity. We compared the network structure to a temporally shuffled null model to examine the importance of social attraction, and checked for persistent characteristic groups over time.

RESULTS

The clustering within the carp social network tended to be more pronounced during daytime than nighttime throughout the year. Social attraction, particularly during daytime, was a key driver for interactions. Shoaling behavior substantially increased during daytime in the wintertime, whereas in summer carp interacted less frequently, but the interaction duration increased. Therefore, smaller, characteristic groups were more common in the summer months and during nighttime, where the social memory of carp lasted up to two weeks.

CONCLUSIONS

We conclude that social relationships of carp change diurnally and seasonally. These patterns were likely driven by predator avoidance, seasonal shifts in lake temperature, visibility, forage availability and the presence of anoxic zones. The techniques we employed can be applied generally to high-resolution biotelemetry data to reveal social structures across other fish species at ecologically realistic scales.

Male zebrafish (Danio rerio) do not preferentially associate with familiar over unfamiliar conspecifics

Members of several shoaling species have been shown to prefer to associate with familiar individuals, enhancing the benefits of aggregation. The authors used a series of social preference tasks in the laboratory to evaluate whether prior familiarity with potential partners influences preference of shoaling partner in male zebrafish (Danio rerio), a social species found in shallow, slow-moving waters. The authors found that though male zebrafish exhibited a strong preference for shoaling with a male conspecific as opposed to remaining alone, they exhibited no preference for familiar over unfamiliar conspecifics. This suggests that the benefits of familiarity for shoaling behaviour may not be as important for male zebrafish as has been shown in other social fish species.

Predation risk shapes the use of conflicting personal risk and social safety information in guppies

When faced with uncertainty, animals can benefit from using multiple sources of information in order to make an optimal decision. However, information sources (e.g., social and personal cues) may conflict, while also varying in acquisition cost and reliability. Here, we assessed behavioral decisions of Trinidadian guppies (Poecilia reticulata), in situ, when presented with conflicting social and personal information about predation risk. We positioned foraging arenas within high- and low-predation streams, where guppies were exposed to a personal cue in the form of conspecific alarm cues (a known indicator of risk), a novel cue, or a control. At the same time, a conspecific shoal (a social safety cue) was either present or absent. When social safety was absent, guppies in both populations showed typical avoidance responses towards alarm cues, and high-predation guppies showed their typical avoidance of novel cues (i.e., neophobia). However, the presence of social safety cues was persuasive, overriding the neophobia of high-predation guppies and emboldening low-predation guppies to ignore alarm cues. Our experiment is one of the first to empirically assess the use of safety and risk cues in prey and suggests a threshold level of ambient risk which dictates the use of conflicting social and personal information.

Social familiarity improves fast-start escape performance in schooling fish

Using social groups (i.e. schools) of the tropical damselfish Chromis viridis, we test how familiarity through repeated social interactions influences fast-start responses, the primary defensive behaviour in a range of taxa, including fish, sharks, and larval amphibians. We focus on reactivity through response latency and kinematic performance (i.e. agility and propulsion) following a simulated predator attack, while distinguishing between first and subsequent responders (direct response to stimulation versus response triggered by integrated direct and social stimulation, respectively). In familiar schools, first and subsequent responders exhibit shorter latency than unfamiliar individuals, demonstrating that familiarity increases reactivity to direct and, potentially, social stimulation. Further, familiarity modulates kinematic performance in subsequent responders, demonstrated by increased agility and propulsion. These findings demonstrate that the benefits of social recognition and memory may enhance individual fitness through greater survival of predator attacks.

The activity of the prelimbic cortex in rats is enhanced during the cooperative acquisition of an instrumental learning task

The objective of this study was to identify the functional properties of the prefrontal cortex that allow animals to work together to obtain a mutual reward. We induced pairs of male rats to develop a cooperative behavior in two adjacent Skinner boxes divided by a metallic grille. The experimental boxes allowed the two rats to see and to smell each other and to have limited physical contact through the grille. Rats were progressively trained to climb onto two separate platforms (and stay there simultaneously for >0.5 s) to get food pellets for both. This set-up was compatible with the in vivo recording of local field potentials (LFPs) at the prelimbic (PrL) cortex throughout the task. A dominant delta/theta activity appeared mostly during the period in which rats were located on the platforms. Spectral powers were larger when rats had to stay together on the platforms than when they jumped individually onto them. When paired together, rats presented significant differences in the power of delta and low theta bands depending if they were leading or following the joint activity. PrL cortex encodes neural commands related to the individual and joint acquisition of an operant conditioning task by behaving rats.

House sparrows' (Passer domesticus) behaviour in a novel environment is modulated by social context and familiarity in a sex-specific manner

Background

Exploratory behaviour is one of the best-investigated behavioural traits. However, little is known about how differences in familiarity, i.e. in the knowledge and previous experience with a companion can influence the exploration of a novel environment. However, to our knowledge, such a critical feature of the social environment has never been the target of a study relating it to exploratory behaviour in birds. Here we examined if familiarity with a conspecific could affect behavioural responses of individuals confronted with a novel environment. We recorded the latency to land on the ground, latency to feed, time spent feeding and number of sectors visited of 48 female and 48 male house sparrows (Passer domesticus) in an indoor aviary in three contexts: alone (individual context), with an unfamiliar and with a familiar same-sex companion.

Results

House sparrows landed sooner on the ground when in the familiar context than when in the individual context. Birds in unfamiliar pairs followed each other less than familiar birds, but this difference diminished with time spent exploring. Moreover, males and females differed in their behavioural responses in the unfamiliar context. Females with a familiar companion landed sooner than when they were paired with an unfamiliar conspecific, whereas only the presence of a companion but not familiarity reduced males latency to land on the ground. Finally, when considering the unfamiliar context males had shorter latencies to forage and thus spent more time eating than females.

Conclusions

The presence or absence of a companion and its familiarity with the focal individual influenced differently the behavioural responses of male and female house sparrows in a novel environment. As house sparrows are strongly sociable, the influence of the social environment is likely to be of paramount importance to understand the selective pressures acting on them, particularly in recently colonized areas with ephemeral food sources. Our results shed light on the complex influence that the social environment has on the behavioural responses of a cosmopolitan bird.

Pair bond endurance promotes cooperative food defense and inhibits conflict in coral reef butterflyfish

Pair bonding is generally linked to monogamous mating systems, where the reproductive benefits of extended mate guarding and/or of bi-parental care are considered key adaptive functions. However, in some species, including coral reef butterflyfishes (f. Chaetodonitidae), pair bonding occurs in sexually immature and homosexual partners, and in the absence of parental care, suggesting there must be non-reproductive adaptive benefits of pair bonding. Here, we examined whether pair bonding butterflyfishes cooperate in defense of food, conferring direct benefits to one or both partners. We found that pairs of Chaetodon lunulatus and C. baronessa use contrasting cooperative strategies. In C. lunulatus, both partners mutually defend their territory, while in C. baronessa, males prioritize territory defence; conferring improvements in feeding and energy reserves in both sexes relative to solitary counterparts. We further demonstrate that partner fidelity contributes to this function by showing that re-pairing invokes intra-pair conflict and inhibits cooperatively-derived feeding benefits, and that partner endurance is required for these costs to abate. Overall, our results suggest that in butterflyfishes, pair bonding enhances cooperative defense of prey resources, ultimately benefiting both partners by improving food resource acquisition and energy reserves.

I remember you: female Siamese fighting fish recognise prior social partners

Recognising social partners allows individuals to establish social networks with one another, informs mating decisions, and decreases energy expenditure. Studies rarely examine if females have this ability outside of mate choice. Additionally, it is unknown if familiarity differs when females encounter females versus males. Female Siamese fighting fish were placed into one of six treatment groups that differed based on the sex of the interactant (female or male) and experience (familiar, unfamiliar or no previous exposure). In both female–female and female–male interactions, less behaviour was performed towards familiar individuals. However, the degree to which familiarity had an effect differed depending on the sex of the interactant and the behaviour measured. Familiarity may serve an important function if it increases an individual’s ability to remember the outcome of prior encounters and use this information in later encounters with the same individual. To fully understand social dynamics, both sexes must be examined.

Effect of elevated carbon dioxide on shoal familiarity and metabolism in a coral reef fish

Atmospheric CO₂ is expected to more than double by the end of the century. The resulting changes in ocean chemistry will affect the behaviour, sensory systems and physiology of a range of fish species. Although a number of past studies have examined effects of CO₂ in gregarious fishes, most have assessed individuals in social isolation, which can alter individual behaviour and metabolism in social species. Within social groups, a learned familiarity can develop following a prolonged period of interaction between individuals, with fishes preferentially associating with familiar conspecifics because of benefits such as improved social learning and greater foraging opportunities. However, social recognition occurs through detection of shoal-mate cues; hence, it may be disrupted by near-future CO₂ conditions. In the present study, we examined the influence of elevated CO₂ on shoal familiarity and the metabolic benefits of group living in the gregarious damselfish species the blue-green puller (Chromis viridis). Shoals were acclimated to one of three nominal CO₂ treatments: control (450 µatm), mid-CO₂ (750 µatm) or high-CO₂ (1000 µatm). After a 4-7 day acclimation period, familiarity was examined using a choice test, in which individuals were given the choice to associate with familiar shoal-mates or unfamiliar conspecifics. In control conditions, individuals preferentially associated with familiar shoal-mates. However, this association was lost in both elevated-CO₂ treatments. Elevated CO₂ did not impact the calming effect of shoaling on metabolism, as measured using an intermittent-flow respirometry methodology for social species following a 17-20 day acclimation period to CO₂ treatment. In all CO₂ treatments, individuals exhibited a significantly lower metabolic rate when measured in a shoal vs. alone, highlighting the complexity of shoal dynamics and the processes that influence the benefits of shoaling.

Social cognition in fishes

Brain evolution has often been correlated with the cognitive demands of social life. Further progress depends on our ability to link cognitive processes to corresponding brain part sizes and structures, and, ultimately, to demonstrate causality. Recent research suggests that fishes are suitable to test general hypotheses about vertebrate social cognition and its evolution: brain structure and physiology are rather conserved among vertebrates, and fish are able to perform complex decisions in social context. Here, we outline the opportunities for experimentation and comparative studies using fish as model systems, as well as some current shortcomings in fish social cognition research.