We are pleased to present the first collection dedicated to highlighting the research of our Editorial Board, entitled Editors' Showcase: Behavioral Development and Play. This exclusive collection is open to Editorial Board members only and will feature high-quality contributions from our Associate and Review Editors. Specialty Chief Editor Professor Christine Drea leads this initiative which will focus on new insights, novel developments, current challenges, latest discoveries, recent advances, and future perspectives in the field of Behavioral Development and Play. The work presented here celebrates the broad diversity of research performed across the section and aims to put a spotlight on all areas of interest to our Editors. This collection aims to further support Frontiers’ strong community by recognizing and promoting the work of highly deserving Editors.

Duke University

Frontiers in Ethology

Behavioral Development and Play

Editors' Showcase: Behavioral Development and Play

Effect of social play deprivation on stress sensitivity in response to social and non-social challenges

Play is a widespread phenomenon in the animal kingdom with observations from all vertebrate classes. The adaptive value of this behaviour, however, remains unclear. In the past century, numerous theories have been put forward, ranging from releasing surplus energy to training species-specific behaviours. However, none of these theories can fully explain the functions of play. A recent neurocognitive theory suggests that play allows the brain to encounter many different and surprising situations that provide it with opportunities to learn about the environment and form predictions about it. This theory has, however, to our knowledge, previously not been experimentally tested. To start exploring the connection between play and cognition, we compared the cognitive capacities of White Leghorn chicks that were stimulated to play in the first five weeks of their lives with chicks that did not receive any play stimulation. More specifically, we wanted to test the connection between specific types of play and cognitive domains. To achieve this, we designed two play treatments: object players that were provided with a variety of toys during their treatment, and social players that were released into an arena with plenty of space and conspecifics, as this has previously been shown to trigger social play. Subsequently, all three treatments (control, object players, social players) were tested in a cognitive test battery consisting of two experiments targeting the social domain and two targeting the physical domain. We found no improvement of cognitive capacities in either play treatment group compared to control subjects, though the social play treatment appears to have affected some behavioural variables recorded during the cognitive tests. Chicks that had played socially were in general bolder, more explorative and had more access to resources in the tests. This might subsequently allow them to exploit their environment more efficiently, which could in turn affect their welfare as they might be more resilient to stress and have more access to resources. More studies will be needed to assess the long-term effects of play on cognitive capacities and welfare of chickens.

Play is a widespread phenomenon in the animal kingdom with observations from all vertebrate classes. The adaptive value of this behaviour, however, remains unclear. In the past century, numerous theories have been put forward, ranging from releasing surplus energy to training species-specific behaviours. However, none of these theories can fully explain the functions of play. A recent neurocognitive theory suggests that play allows the brain to encounter many different and surprising situations that provide it with opportunities to learn about the environment and form predictions about it. This theory has, however, to our knowledge, previously not been experimentally tested. To start exploring the connection between play and cognition, we compared the cognitive capacities of White Leghorn chicks that were stimulated to play in the first five weeks of their lives with chicks that did not receive any play stimulation. More specifically, we wanted to test the connection between specific types of play and cognitive domains. To achieve this, we designed two play treatments: object players that were provided with a variety of toys during their treatment, and social players that were released into an arena with plenty of space and conspecifics, as this has previously been shown to trigger social play. Subsequently, all three treatments (control, object players, social players) were tested in a cognitive test battery consisting of two experiments targeting the social domain and two targeting the physical domain. We found no improvement of cognitive capacities in either play treatment group compared to control subjects, though the social play treatment appears to have affected some behavioural variables recorded during the cognitive tests. Chicks that had played socially were in general bolder, more explorative and had more access to resources in the tests. This might subsequently allow them to exploit their environment more efficiently, which could in turn affect their welfare as they might be more resilient to stress and have more access to resources. More studies will be needed to assess the long-term effects of play on cognitive capacities and welfare of chickens.

The effects of play stimulation on cognitive capacities of chickens

Play behavior is common in a range of mammalian species and can have important influences on early development. We evaluated possible influences of social play on the development of behavior along the caution/boldness continuum in juvenile Belding’s ground squirrels (Urocitellus beldingi). We disrupted juvenile squirrels engaged in play by walking toward them until their play interactions stopped. We used undisrupted juveniles and juveniles disrupted while not engaged in play as controls. Caution was measured with behavioral tests during which a human intruder walked toward a squirrel and recorded the distances at which the squirrel first noticed and then fled from the intruder. Rates of social play were lower and play bouts were shorter in play-disrupted juveniles than in undisrupted and nonplay-disrupted juveniles. The distances at which juveniles noticed and fled from an intruder increased across the developmental period in which play primarily occurs, suggesting increases in caution across this interval. Increases in the distances to notice and flee from an intruder did not differ between undisrupted and nonplay-disrupted juveniles, but were greater in these groups than in play-disrupted juveniles. These results are consistent with social play behavior contributing to the development of cautious responses in juvenile U. beldingi.

Play behavior is common in a range of mammalian species and can have important influences on early development. We evaluated possible influences of social play on the development of behavior along the caution/boldness continuum in juvenile Belding’s ground squirrels (Urocitellus beldingi). We disrupted juvenile squirrels engaged in play by walking toward them until their play interactions stopped. We used undisrupted juveniles and juveniles disrupted while not engaged in play as controls. Caution was measured with behavioral tests during which a human intruder walked toward a squirrel and recorded the distances at which the squirrel first noticed and then fled from the intruder. Rates of social play were lower and play bouts were shorter in play-disrupted juveniles than in undisrupted and nonplay-disrupted juveniles. The distances at which juveniles noticed and fled from an intruder increased across the developmental period in which play primarily occurs, suggesting increases in caution across this interval. Increases in the distances to notice and flee from an intruder did not differ between undisrupted and nonplay-disrupted juveniles, but were greater in these groups than in play-disrupted juveniles. These results are consistent with social play behavior contributing to the development of cautious responses in juvenile U. beldingi.

Disruption of social play influences development of caution in juvenile ground squirrels

Play fighting has been one of the most intensely studied forms of play and so has provided some of our deepest insights into the understanding of play in general. As the label implies, this behavior resembles serious fighting, in that the animals compete for an advantage over one another, but unlike true aggression, for play fighting to remain playful, it also incorporates a degree of cooperation and reciprocity – restrained competition seems to be its hallmark. Despite these common features, it should be noted that both the advantage competed over and the mechanisms by which restraint is achieved varies across species. Such variation mitigates simple generalities. For example, how empirical support for a proposed adaptive function in one species not being replicated in another, is to be interpreted. What has emerged over the past few decades is that play fighting is diverse, varying across several dimensions, some superficial, some fundamental, making choosing species to compare a challenge. In this paper, we explore various design features that constitute play fighting and the ways these can be modified across different species and lineages of species. Given that a major pillar of ethology is that description precedes explanation, having a good grasp of the behavioral diversity of play fighting is an essential starting point for detailed analyses of the mechanisms and functions of play. We show that commonalities across species likely involve different mechanisms than do species idiosyncrasies, and that different styles of play fighting likely afford different adaptive opportunities.

Play fighting has been one of the most intensely studied forms of play and so has provided some of our deepest insights into the understanding of play in general. As the label implies, this behavior resembles serious fighting, in that the animals compete for an advantage over one another, but unlike true aggression, for play fighting to remain playful, it also incorporates a degree of cooperation and reciprocity &#x2013; restrained competition seems to be its hallmark. Despite these common features, it should be noted that both the advantage competed over and the mechanisms by which restraint is achieved varies across species. Such variation mitigates simple generalities. For example, how empirical support for a proposed adaptive function in one species not being replicated in another, is to be interpreted. What has emerged over the past few decades is that play fighting is diverse, varying across several dimensions, some superficial, some fundamental, making choosing species to compare a challenge. In this paper, we explore various design features that constitute play fighting and the ways these can be modified across different species and lineages of species. Given that a major pillar of ethology is that description precedes explanation, having a good grasp of the behavioral diversity of play fighting is an essential starting point for detailed analyses of the mechanisms and functions of play. We show that commonalities across species likely involve different mechanisms than do species idiosyncrasies, and that different styles of play fighting likely afford different adaptive opportunities.