Behavioural Processes

Rats are highly social mammals that form social groups of various sizes. Interestingly, they are known to show prosocial behaviors, and are socially tolerant of other conspecifics as they feed together, but the specificity of their prosociality has not been fully understood. Here, we investigated what degree rats showed social choice, i.e., preferential joint feeding even with unfamiliar animals by performing a simple feeding site choice task. In the task, subjects were tested to choose between the feeding site where they fed with other rats (social option) or the other site where they could feed alone (solitary option). The results showed that social option choices increased particularly when the partner was a single non-cagemate rat. This result means that high social preference for other individuals occurs spontaneously, even when they are feeding with unfamiliar non-cagemates. This high degree of social tolerance would lead to the suppression of aggressive behavior as well as enhancement of affiliative relationships even in situations when the rats met with unfamiliar conspecifics for the first time. HighlightsO_LIRats are highly socially tolerant mammals as they feed with conspecifics together. C_LIO_LIWe explored how the presence of conspecifics affects feeding site choices in rats. C_LIO_LISocial choices increased when the partners were non-cagemates. C_LIO_LISocial choices decreased as the number of non-cagemates increased. C_LIO_LIJoint feeding with a single non-cagemate is observed particularly frequently. C_LI

Environmental enrichment (EE) consists of a series of interventions that are carried out in the home environment to provide greater exposure to sensory stimuli with the objective of mimicking the natural habitat for the animals housed in the laboratory, offering a more complex environment like those found in nature. Some studies have shown the positive effects of EE on zebrafish housed in a laboratory environment. However, this evidence is still very recent and accompanied by contradictory results. Furthermore, there is great variability in the protocols applied, and in the conditions of the tests, tanks, and materials used for creating an EE environment. This substantial variability can bring many uncertainties to the development of future studies and hinder the reproducibility and replicability of research. In this context, the main objective of this study was to carry out a systematic review of the literature aiming to provide an overview of the EE protocols used in zebrafish. We conducted a systematic review following PRISMA recommendations. The literature search was performed in PubMed, Scopus, and Web of Science databases and the studies were selected based on inclusion/exclusion criteria. We performed data extraction and risk of bias analysis of the studies included. A total of 901 articles were identified in the databases and 27 of these studies were included in this review. Among these studies, the effect of EE was evaluated as two different proposals. (1) to improve animal welfare and (2) as an intervention for the prevention of some disorders. Although the zebrafish EE protocols presented a series of experimental differences, the results showed that the benefits of the EE for zebrafish were robust. According to the results described here, the use of EE in the zebrafish home tank provides better welfare and may reduce sources of bias in scientific experiments, such as high-stress levels and fighting events.

Social play is a motivating and rewarding behavior displayed by juveniles of many mammalian species, including humans and rats. Social play is vital to the development of social skills. Autistic children show less social play engagement which may contribute to their impairments in social skills. There is limited knowledge about what external conditions may positively or negatively influence social play engagement in humans or other animals. Therefore, we determined how two common external conditions, playmate familiarity and social isolation, modulate social play levels and social play defense tactics in juveniles of three common laboratory rat strains: Long-Evans, Sprague-Dawley, and Wistar. Males and females were socially isolated for either 2h or 48h prior to social play testing and were then exposed to either a familiar (cage mate) or novel playmate, creating four testing conditions: 2h-Familiar, 48h-Familiar, 2h-Novel, and 48h-Novel. Both playmate familiarity and social isolation length influenced social play behavior levels and tactics in juvenile rats, but did so differently for each of the three rat strains. Long-Evans played most with a familiar playmate, irrespective of time isolated, Sprague-Dawley played most in the 48h-Familiar condition, and Wistar played the least in the 2h-Familiar condition, but Wistar played more with a novel playmate than Long-Evans and Sprague-Dawley. Analysis of social play tactics by the playmates in response to nape attacks by the experimental rats revealed strain differences with novel playmates. Here, Sprague-Dawley and Wistar defended more nape attacks than Long-Evans. Sprague-Dawley evaded these attacks, thereby shortening body contact. In contrast, Wistar turned to face their playmate attacker and showed more complete rotations, thereby extending body contact and wrestling longer. Role reversals, which increase social play reciprocity and reflect the quality of social play, were higher in Long-Evans and Sprague-Dawley with familiar playmates. Role reversals decreased for Sprague-Dawley but increased for Wistar after 48h isolation. The effects of playmate familiarity or social isolation length on social play levels and tactics were similar across sex for all three strains. In conclusion, we showed that two common external factors (playmate familiarity and social isolation length) that largely vary across social play studies have a major impact on the level and quality of social play in the three rat strains. Strain differences indicate higher level and quality of social play with familiar playmates in Long-Evans, with familiar playmates after short isolation in Sprague-Dawley, and with novel playmates after longer isolation for Wistar. Future research could determine whether strain differences in neuronal mechanisms underlie these condition-induced variations in social play engagement. Our findings are also informative in suggesting that external conditions like playmate familiarity and social isolation length could influence social play levels and social play quality in typical and atypical children.

Swimway and open field are the two popular apparatus used for measuring boldness - the propensity to take risky decisions - in various piscine species. The present study compared boldness exhibited by an air breathing freshwater fish climbing perch in a swimway, rectangular open field, intermediate stages between these two apparatus and circular open field. Impact of the modification of the start chamber by providing substratum made up of cobbles and covering the water surface using water plant hydrilla, alone and in combinations on the boldness was also tested. Our results revealed that the apparatus has a significant impact on the boldness in climbing perch. The presence of a shelter in the experimental arena (swimway) and cobble substratum in the start chamber of the apparatus were found to be reducing boldness in this fish, while hydrilla cover on the water surface neutralised the impact of cobble substratum. Repeated exposure and resultant familiarity with the arena increased boldness of climbing perch but the pattern of modification of this behavioural trait exhibited during the course of experiment was divergent across the instruments. These results point towards the need for critically analyzing the influence of instruments used for measuring various behavioural traits and considering biological needs of the subject species while designing the apparatus.

The effect of incorporating a fixed consecutive number (FCN) procedure in interresponse time (IRT) shaping using a discrete-trial percentile schedule was examined. Eight pigeons were used. On each trial, pigeons were required to peck the IRT start key and then the IRT end key. Reinforcers were presented according to the percentile schedule based on the time interval (IRT) or the cumulative response count to the IRT start key during those two key pecks. Multiple responses to the IRT start key were allowed only in the condition incorporating the FCN procedure. Results showed that incorporating the FCN procedure improved the success of IRT shaping from 1/8 to 7/8 of the pigeons. The procedure developed in this study provides an ideal baseline for studying response shaping with IRT as the dependent variable.

Mate search tactics and association preferences among organisms in natural habitats can be dynamic and are determined by inherent trait preferences as well as the cost-benefit trade-offs associated with each mating decision. Two of the prime factors regulating mating decisions are the presence of competing conspecifics and predatory threats, both of which have important fitness consequences for the individual. We studied the influence of these two factors separately in mate search tactics and association preferences among zebrafish males. Male zebrafish were presented with a choice of two patches, consisting of different number of females, of which one patch was also associated with a predatory threat. We found that males made a preferential choice for the patch with more number of females only when the numerical difference between choices are starkly different, irrespective of the predatory threat associated with the patch. This points towards the role of numerical cognition in assessing cost-benefit tradeoffs in male zebrafish. We also studied the association preference of males in a multi-choice setup, consisting of four separate mixed-sex groups of zebrafish varying in densities. Our results showed that while test males preferred to visit the male-biased patches more often, they spent more time near female-biased patches or patches with equal sex ratio patches indicating the role of complex interplay of social cues in determining the associative behavior of males to a patch. This study, thus, sheds further light on the interactive roles of social cues and cognitive abilities in mate association patterns in this species.

A pilot study demonstrating complex cognitive abilities of altruism in rats by observing if rats would voluntarily put themselves in distress solely in order to help another conspecific irrespective of kinship and without any expectation of reward in terms of food or mate in return.

In behavior analysis, the modulation of the effect of time-based schedules by the spatial characteristics of the environment has been scarcely studied. Furthermore, the spatial organization of behavior, despite its ubiquity and ecological relevance, has not been widely addressed. The purpose of the present work was to analyze the effect of water delivery location (peripheral vs. central) on the spatial organization of water-feeding behavior under time-based schedules. One group of rats was exposed to a Fixed Time 30 s-water-delivery schedule and a second group to a Variable Time 30 s schedule. For both groups, in the first phase, the water dispenser was located in the perimetral zone. In the second condition, the water dispenser was located in the central zone. Each location was presented for 20 sessions. Rats trajectories, distance to the dispenser, accumulated time in regions, and entropy measures were analyzed. A differential effect of the location of water delivery in interaction with the time-based schedule was observed on all the analyzed spatial qualities of behavior. The findings are discussed in relation to the ecological proposal of Timberlakes behavioral systems.

Animals differ in their ability to learn. One potential factor contributing to learning differences is personality types. We investigated the relationship between learning and the bold-shy continuum by comparing performance of bold and shy zebrafish in conditioned place preference (CPP) and 2 choice tasks. Bold fish learned significantly faster than the shy fish but there were no differences in their final performance. When tested in the 2 choice task, we found no clear evidence of learning, however bold fish made more initial choices than shy fish. Overall,our study suggests that bold fish tend to be faster learners when compared to shy fish. The lack of differences in the final change in behavior suggests that the learning difference is due to neophobic tendencies and resulting initial interactions with the learning stimulus.

Same-sex affiliative relationships are common in humans and some social animals, forming one of the bases of group living. The neuropeptide vasopressin (VP) and its receptors mediate these relationships and behaviours in mammals and birds with gregarious and colonial social structures. In some species, affiliative relationships between dominant and subordinate individuals can be maintained while still retaining strict dominance hierarchies where three or more individuals interact. However, it is unclear whether triadic interaction promotes these relationships, and whether the VP system is also involved in such affiliations due to the lack of suitable animal models and experimental settings. This study addresses these questions with two experiments. In Experiment 1, two-week cohabitation among three male crows facilitated affiliative relationships in particular dyads within each triad. In Experiment 2, vasopressin 1a receptor (V1aR) antagonism disrupted affiliative behaviours and led to the resurgence of agonistic behaviours in affiliated males but not in unaffiliated ones by peripherally administering a V1aR antagonist. These findings suggest that the VP system might universally mediate same-sex affiliative relationships, despite differences in inherent aggression levels among individuals. The triadic cohabitation paradigm established here could advance our understanding of animal societies and be applied across various species, sexes, and social structures. Impact statementThis study provides evidence that a triadic interactive environment facilitates the formation of affiliative relationship between specific dominant and subordinate males in large-billed crows, with crucial involvement of vasopressin 1a receptor in maintaining this affiliation.

Previous studies suggest that vocal-learning species use variations of prosodic cues, such as changes in pitch, amplitude, or duration, in the conveying of meaning and emotions as well as individual recognition. Although it is known that the long-distance contact calls ("phee" calls) of common marmosets, a vocal non-learner, vary in prosodic information depending on individual characteristics, evidence of the species use of this information only recently started to emerge. In this study we tested 18 captive common marmosets (Callithrix jacchus) reactions to playbacks of familiar and unfamiliar individuals phee calls and extracted pitch-contour information. The playbacks consisted of i) natural phee calls from group members or unfamiliar conspecifics, or ii) synthesized pitch contours of familiar or unfamiliar phee calls following a natural or artificial syllable order as well as pure tones of similar frequency and duration. We found that although individuals seemed to show different reactions towards the natural calls of familiar and unfamiliar individuals, we did not find group level differences. Marmosets furthermore show significantly reduced interest in synthesized pitch contours compared to natural phee calls and did not differentiate between pitch contour playbacks and pure tone control stimuli, indicating that they did not categorize the pitch contours as conspecific calls. Our results suggest that extracted pitch contour information alone is not sufficient for marmosets to recognise conspecifics, however further studies are required to investigate the exact mechanism of individual recognition in marmosets.

Spatiotemporal dynamics of behavior is key to understanding the organism-environment relationship. While often implicitly addressed, its relation to Pavlovian contingencies remains understudied in domestic dogs. This study quantitatively examined the spatial dimension of behavior of three freely moving dogs under pairing and extinction of a tone-food Pavlovian contingency. In pairing, a tone (CS) was paired with food delivery (US) on a fixed-time 60-second (FT 60 s) schedule; in extinction, only the tone was presented. Locomotion was recorded using two-dimensional tracking based on center of mass. During pairing, dogs moved closer to the dispenser, covered greater distances, displayed extended trajectories, and showed a conditional approach pattern to the dispenser during CS presentation. In extinction, they stayed closer to the owner or room periphery, traveled shorter distances, and exhibited more restricted trajectories. These findings show that spatial segments (dispenser area) are integrated into the CS-US relationship, demonstrate the usefulness of continuous recording of spatial behavior in the analysis of Pavlovian contingencies, and suggest potential application in contexts relevant to animal welfare. HighlightsO_LISpatial behavior remains largely unexplored in studies of Pavlovian contingencies C_LIO_LIDog locomotion was continuously tracked during pairing and extinction phases C_LIO_LIDistinct spatial patterns emerged across pairing and extinction phases C_LIO_LIIncorporating space into CS-US relations clarifies behavioral organization C_LIO_LITracking tools expand the experimental and applied scope of Pavlovian research C_LI

In rodents, young pups communicate with their parents through harmonic calls and ultrasonic vocalizations (USVs). These forms of communication can improve chances of survival, since pups rely on their parents for thermoregulation, nutrition and protection. The extent to which pups modulate calls in response to their surroundings remains unclear. In this study we examined whether olfactory stimuli influence characteristics of pup calls, and how these calls may be affected by pup sex and litter size, in the California mouse (Peromyscus californicus). Pups were isolated and audio recorded during an initial, 3-minute control period, after which they were exposed for 5 minutes to bedding containing one of 4 olfactory cues: scent from their home cage, scent from the home cage of an unfamiliar family, coyote urine, or no scent. Latency to call, call rate, call duration and call characteristics (e.g. frequency and amplitude) were compared between the control period and olfactory-exposure period as well as among olfactory conditions. Pups from 2-pup litters called more quietly (lower amplitude) when exposed to odor from a predator while pups from 3-pup litters called louder (higher amplitude). Additionally, pups tended to reduce their call rates in response to odors from their home cage, consistent with contact quieting. However, pups tended to increase their rate of calling when exposed to predator urine, in contrast to the expectations of predator-induced vocal suppression. Lastly, male pups produced higher-frequency calls and more USVs than females. These results indicate that a number of pup call characteristics in this species can be influenced by acute olfactory stimuli as well as factors such as litter size and sex. The value of these pup call variations for offspring-parent communication is unclear: whether they elicit different parental responses is unknown and would be an interesting/valuable/informative avenue for future studies.

Pup retrieval is a critical maternal behavior ensuring pup survival. Its mechanisms have been studied mainly in rodents, where mothers tolerate brief pup separation. In contrast, in species for which even short separation is life-threatening, mothers maintain constant physical contact, reinforcing anti-separation behavior. Studying such species may uncover maternal strategies under survival-critical extremes. Among these species, echolocating bats provide an ideal model for acoustic-based decision-making, as they rely heavily on sound. In bats, pup isolation calls (ICs) are essential signals in mother-pup communication. To assess their motivation in retrieval based on ICs, we conducted behavioral experiments: (1) pup retrieval test, and (2) playback test using ICs from own vs. non-own pups. Each was conducted under three maternal conditions: holding (a) no-pup, (b) one-pup, and (c) two-pup, to assess tactile influence on maternal motivation. Mothers responded only during periods of high-rate ICs vocalization and showed selective responsiveness to their own pups. ICs alone were sufficient to elicit maternal responses, acted as decisive communicative triggers for maternal response. Maternal responses were strongly suppressed under condition (c), but robustly expressed under conditions (a) and (b). These findings suggest that maternal motivation is governed by a decision-making threshold, whereby internal motivation induced by pup loss is amplified by ICs, a decisive trigger for retrieval--providing insight into instinctive maternal behavior in mammals.

Early life environment influences the development of various aspects of social behavior, particularly during sensitive developmental periods. Here, we aimed to study how challenges in the early postnatal period or (early) adolescence affect pro-social behavior. To this end, we adapted an existing paw operated liberation task to an automated operant task, to measure motivation (by progressively increasing required lever pressing) to liberate a trapped conspecific. Liberation of the trapped rat resulted either in social contact, or in liberation into a separate compartment. Additionally, a condition was tested in which both rats could freely move in two separate compartments and lever pressing resulted in social contact. When partners were not trapped, rats were more motivated to press the lever for opening the door than in either of the trapped configurations. Contrary to our expectation, the trapped configuration resulted in a reduced motivation to act. Early postnatal stress (24h maternal deprivation on postnatal day 3) did not affect behavior in the liberation task. However, rearing rats from early adolescence onwards in complex housing conditions (Marlau cages) reduced the motivation to door opening, both in the trapped and freely moving conditions, while motivation for a sucrose reward was not affected.

Humans show distinct social behaviours when we recognise social similarity in opponents that are members of the same social group. However, little attention has been paid to the role of social similarity in non-human animals. In Wistar subject rats, the presence of an unfamiliar Wistar rat mitigated stress responses, suggesting the importance of social similarity in this phenomenon. We found that the presence of unfamiliar Sprague-Dawley (SD) or Long-Evans (LE) rats, but not an unfamiliar Fischer 344 (F344) rat, similarly mitigated stress in subject rats. It is therefore possible that the subject rats recognised social similarity to unfamiliar SD and LE rats. In this study, we demonstrated that Wistar subject rats were capable of categorizing unfamiliar rats based on their strain, and that Wistar subjects showed a preference for unfamiliar Wistar, SD, and LE rats over F344 rats. However, the subject rats did not show a preference among Wistar, SD, and LE rats. In addition, the results were not due to an aversion to F344 rats, and preference was not affected when anaesthetised rats were presented to subject rats. The findings suggested that rats recognise social similarity to certain unfamiliar strains of rats.

Previous research has shown that humans can discriminate two individual rhesus monkeys (Macaca mulatta), as well as two individual zebra finches (Taeniopygia guttata) by their vocalizations. The discrimination of individual zebra finches largely relies on differences in pitch contour, although this is not the only relevant cue. The purpose of the present experiment was to examine whether humans can also discriminate two individual large-billed crows (Corvus macrorhynchos) by their calls. Discrimination was tested with a forced-choice Same-Different Paradigm. Results show a high discrimination accuracy without prior training, although the scores obtained here were lower than those in the zebra finch discrimination task. There was no significant learning trend across trials. Future studies should investigate which acoustic cues participants use for the discrimination of individual crows and expand these findings with more non-human animal vocalizations.

Freediving in rats has emerged as a relevant model to study physiology and neural adaptation underlying submersion mechanisms. However, despite well-established strain-dependent differences in behaviour and physiological responses, most studies about freediving rely on Sprague Dawley rats. As the choice of strain could significantly shape experimental results depending on the field of research, we conducted a behavioural comparative study between Long Evans (LE) rats, genetically closer to the Wild Norway rat, with the commonly used Sprague Dawley (SD) strain. We developed an 11-week progressive voluntary freediving protocol involving four distances (from 5 to 11 meters), and assessed the rats natural willingness to dive and swim, and identified several parameters for evaluation of their confidence (waiting time before diving, speed), performance capacity (freediving time) and population variability. We found that Long Evans rats were naturally more willing to dive and more confident, compared to Sprague Dawley rats: they showed better performance with longer time underwater and slower diving speed. We also uncover differences in their variability, at trial-to-trial intra-individual and population inter-individual levels, which can guide the choice of one strain over the other, depending on the aim of the scientific inquiry. HighlightsO_LILong Evans rats were naturally more willing and confident at the beginning of the freediving training. C_LIO_LILong Evans freedivers showed greater ease in the water during the course of training compared to Sprague Dawleyfreedivers. C_LIO_LILong Evans freedivers demonstrated greater inter- and intra-individual variability. C_LI

Both mental and physiological conditions determine the well-being state in an animal. Enrichment is a way to increase an animals well-being and may require problem solving through thinking, tolerance of ambiguity, openness, and intrinsic motivation. It is unclear if it is enriching when an animal participates in different types of research. Therefore, it is important to answer the question of whether research can be used as an enrichment tool in zoological facilities. Here, we examine if participation in psychophysical research affected the mental stimulation of three grey seals under human care. The effects varied amongst the three individuals that took part in the research, and indicated that their participation in the research task was dependent on their individual personalities and life history. Two seals indicated that their involvement in the research was positive and motivating, and therefore can be considered enriching. In comparison, the third seal displayed a tendency for frustration and low motivation. Our results indicate that research can be a powerful enrichment tool with animals that find research motivating.

It is established that p-cresol, a compound produced by bacterial colonies within the gastrointestinal tract of mammals, plays a contributory role in the manifestation of various mental disorders. Recently, our research demonstrated that diminishing p-cresol levels in the brain adversely impact the behavioral manifestation of cognitive abilities in rats. In this study, we aimed to investigate the impact of augmenting p-cresol levels in the brain on learning. The Active Avoidance Test was employed to assess learning capabilities. The results, with a high level of confidence, indicated that rats with an increased concentration of p-cresol in the brain exhibited superior task performance and accelerated learning compared to the control group.