Aggression, rank and power: why hens (and other animals) do not always peck according to their strength

Thorlief Schjelderup-Ebbe's seminal paper on the ‘pecking’ order of chickens inspired numerous ethologists to research and debate the phenomenon of dominance. The expansion of dominance to the broader concept of power facilitated disentangling aggression, strength, rank and power. Aggression is only one means of coercing other individuals, and can sometimes highlight a lack of power. The fitness advantages of aggression may only outweigh the costs during periods of uncertainty. Effective instruments of power also include incentives and refusals to act. Moreover, the stability of the power relationship might vary with the instruments used if different means of power vary in the number and types of outcomes achieved, as well as the speed of accomplishing those outcomes. In well-established relationships, actions or physiological responses in the subordinate individual may even be the only indicator of a power differential. A focus on strength, aggression and fighting provides an incomplete understanding of the power landscape that individuals actually experience. Multiple methods for constructing hierarchies exist but greater attention to the implications of the types of data used in these constructions is needed. Many shifts in our understanding of power were foreshadowed in Schjelderup-Ebbe's discussion about deviations from the linear hierarchy in chickens. This article is part of the theme issue ‘The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies’.

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DomArchive: a century of published dominance data

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2020.0436 ◽

2022 ◽

Vol 377 (1845) ◽

Author(s):

Eli D. Strauss ◽

Alex R. DeCasien ◽

Gabriela Galindo ◽

Elizabeth A. Hobson ◽

Daizaburo Shizuka ◽

...

Keyword(s):

Best Practices ◽

Comparative Studies ◽

R Package ◽

Behavioural Ecology ◽

Future Prospects ◽

Theme Issue ◽

Pecking Order ◽

Dominance Hierarchies ◽

Current State ◽

And Function

Dominance behaviours have been collected for many groups of animals since 1922 and serve as a foundation for research on social behaviour and social structure. Despite a wealth of data from the last century of research on dominance hierarchies, these data are only rarely used for comparative insight. Here, we aim to facilitate comparative studies of the structure and function of dominance hierarchies by compiling published dominance interaction datasets from the last 100 years of work. This compiled archive includes 436 datasets from 190 studies of 367 unique groups (mean group size 13.8, s.d. = 13.4) of 135 different species, totalling over 243 000 interactions. These data are presented in an R package alongside relevant metadata and a tool for subsetting the archive based on biological or methodological criteria. In this paper, we explain how to use the archive, discuss potential limitations of the data, and reflect on best practices in publishing dominance data based on our experience in assembling this dataset. This archive will serve as an important resource for future comparative studies and will promote the development of general unifying theories of dominance in behavioural ecology that can be grounded in testing with empirical data. This article is part of the theme issue ‘The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies’.

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The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2020.0432 ◽

2022 ◽

Vol 377 (1845) ◽

Author(s):

Eli D. Strauss ◽

James P. Curley ◽

Daizaburo Shizuka ◽

Elizabeth A. Hobson

Keyword(s):

Full Range ◽

Individual Characteristics ◽

Future Prospects ◽

Theme Issue ◽

Pecking Order ◽

Dominance Hierarchies ◽

Current State ◽

Species Characteristics ◽

Foundational Work ◽

Analytical Approaches

A century ago, foundational work by Thorleif Schjelderup-Ebbe described a ‘pecking order’ in chicken societies, where individuals could be ordered according to their ability to exert their influence over their group-mates. Now known as dominance hierarchies, these structures have been shown to influence a plethora of individual characteristics and outcomes, situating dominance research as a pillar of the study of modern social ecology and evolution. Here, we first review some of the major questions that have been answered about dominance hierarchies in the last 100 years. Next, we introduce the contributions to this theme issue and summarize how they provide ongoing insight in the epistemology, physiology and neurobiology, hierarchical structure, and dynamics of dominance. These contributions employ the full range of research approaches available to modern biologists. Cross-cutting themes emerging from these contributions include a focus on cognitive underpinnings of dominance, the application of network-analytical approaches, and the utility of experimental rank manipulations for revealing causal relationships. Reflection on the last 100 years of dominance research reveals how Schjelderup-Ebbe's early ideas and the subsequent research helped drive a shift from an essentialist view of species characteristics to the modern recognition of rich inter-individual variation in social, behavioural and physiological phenotypes. This article is part of the theme issue ‘The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies’.

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Costs dictate strategic investment in dominance interactions

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2020.0447 ◽

2022 ◽

Vol 377 (1845) ◽

Cited By ~ 5

Author(s):

Tobit Dehnen ◽

Danai Papageorgiou ◽

Brendah Nyaguthii ◽

Wismer Cherono ◽

Julia Penndorf ◽

...

Keyword(s):

Lower Cost ◽

Social Groups ◽

Theme Issue ◽

Pecking Order ◽

Dominance Hierarchies ◽

Strategic Investment ◽

Aggressive Interactions ◽

Current State ◽

Dominance Interactions ◽

Group Members

Dominance is important for access to resources. As dominance interactions are costly, individuals should be strategic in whom they interact with. One hypothesis is that individuals should direct costly interactions towards those closest in rank, as they have most to gain—in terms of attaining or maintaining dominance—from winning such interactions. Here, we show that male vulturine guineafowl ( Acryllium vulturinum ), a gregarious species with steep dominance hierarchies, strategically express higher-cost aggressive interactions towards males occupying ranks immediately below themselves in their group's hierarchy. By contrast, lower-cost aggressive interactions are expressed towards group members further down the hierarchy. By directly evaluating differences in the strategic use of higher- and lower-cost aggressive interactions towards competitors, we show that individuals disproportionately use highest-cost interactions—such as chases—towards males found one to three ranks below themselves. Our results support the hypothesis that the costs associated with different interaction types can determine their expression in social groups with steep dominance hierarchies. This article is part of the theme issue ‘The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies’.

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Emergence of size-structured dominance hierarchies through size-dependent feedback

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2020.0449 ◽

2022 ◽

Vol 377 (1845) ◽

Author(s):

Ian M. Hamilton ◽

Macie D. Benincasa

Keyword(s):

Size Structure ◽

Dynamic Game ◽

Optimal Investment ◽

Growth Suppression ◽

Pecking Order ◽

Dominance Hierarchies ◽

Size Dependent ◽

Current State ◽

Dominance Structure ◽

Competition For Food

Size-based dominance hierarchies influence fitness, group size and population dynamics and link dominance structure to evolutionary and ecological outcomes. While larger individuals often gain dominance, social status may influence growth and size in return, resulting in feedbacks among status, growth and size. Here, we present two models evaluating how these feedbacks influence the emergence of size structure in a dominance hierarchy. In the first, size influences competition for food and investment in suppressing growth of groupmates. Stable size differences emerged when suppression was greatest for similarly sized individuals and size had little effect on competition for food. The model predicted size divergence when size strongly affected competition for food. In the second model, we used a dynamic game to solve for optimal investment in growth suppression as a function of size structure. Investment in growth suppression was favoured only when dominants and subordinates were similar in size, generating size ratios different than those expected by chance. Variation in the feedbacks among growth, size and status can explain variation in emergent size structure of dominance hierarchies and its consequences for conflict within groups. This article is part of the theme issue ‘The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies’.

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Dominance in humans

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2020.0451 ◽

2022 ◽

Vol 377 (1845) ◽

Author(s):

Tian Chen Zeng ◽

Joey T. Cheng ◽

Joseph Henrich

Keyword(s):

Evolutionary Biology ◽

High Status ◽

Pecking Order ◽

Social Hierarchies ◽

Dominance Hierarchies ◽

Institutional Power ◽

Specific Effects ◽

Current State ◽

Behavioural Patterns ◽

Specific Factors

Dominance captures behavioural patterns found in social hierarchies that arise from agonistic interactions in which some individuals coercively exploit their control over costs and benefits to extract deference from others, often through aggression, threats and/or intimidation. Accumulating evidence points to its importance in humans and its separation from prestige—an alternate avenue to high status in which status arises from information (e.g. knowledge, skill, etc.) or other non-rival goods. In this review, we provide an overview of the theoretical underpinnings of dominance as a concept within evolutionary biology, discuss the challenges of applying it to humans and consider alternative theoretical accounts which assert that dominance is relevant to understanding status in humans. We then review empirical evidence for its continued importance in human groups, including the effects of dominance—independently of prestige—on measurable outcomes such as social influence and reproductive fitness, evidence for specialized dominance psychology, and evidence for gender-specific effects. Finally, because human-specific factors such as norms and coalitions may place bounds on purely coercive status-attainment strategies, we end by considering key situations and contexts that increase the likelihood for dominance status to coexist alongside prestige status within the same individual, including how: (i) institutional power and authority tend to elicit dominance; (ii) dominance-enhancing traits can at times generate benefits for others (prestige); and (iii) certain dominance cues and ethology may lead to mis-attributions of prestige. This article is part of the theme issue ‘The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies’.

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The build-up of dominance hierarchies in eusocial insects

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2020.0437 ◽

2022 ◽

Vol 377 (1845) ◽

Cited By ~ 1

Author(s):

Hiroyuki Shimoji ◽

Shigeto Dobata

Keyword(s):

Division Of Labour ◽

Pecking Order ◽

Dominance Hierarchies ◽

Eusocial Insects ◽

Network Analyses ◽

Current State ◽

Individual Memory ◽

Behavioural Interactions ◽

Selective Forces ◽

Reproductive Division

Reproductive division of labour is a hallmark of eusocial insects. However, its stability can often be hampered by the potential for reproduction by otherwise sterile nest-mates. Dominance hierarchy has a crucial role in some species in regulating which individuals reproduce. Compared with those in vertebrates, the dominance hierarchies in eusocial insects tend to involve many more individuals, and should require additional selective forces unique to them. Here, we provide an overview of a series of studies on dominance hierarchies in eusocial insects. Although reported from diverse eusocial taxa, dominance hierarchies have been extensively studied in paper wasps and ponerine ants. Starting from molecular physiological attributes of individuals, we describe how the emergence of dominance hierarchies can be understood as a kind of self-organizing process through individual memory and local behavioural interactions. The resulting global structures can be captured by using network analyses. Lastly, we argue the adaptive significance of dominance hierarchies from the standpoint of sterile subordinates. Kin selection, underpinned by relatedness between nest-mates, is key to the subordinates' acceptance of their positions in the hierarchies. This article is part of the theme issue ‘The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies’.

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Neural systems that facilitate the representation of social rank

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2020.0444 ◽

2022 ◽

Vol 377 (1845) ◽

Cited By ~ 2

Author(s):

Madeleine F. Dwortz ◽

James P. Curley ◽

Kay M. Tye ◽

Nancy Padilla-Coreano

Keyword(s):

Social Rank ◽

Model Organisms ◽

Neural Systems ◽

Learning Mechanisms ◽

Pecking Order ◽

Approach And Avoidance ◽

Dominance Hierarchies ◽

Current State ◽

The Brain ◽

Unique Individual

Across species, animals organize into social dominance hierarchies that serve to decrease aggression and facilitate survival of the group. Neuroscientists have adopted several model organisms to study dominance hierarchies in the laboratory setting, including fish, reptiles, rodents and primates. We review recent literature across species that sheds light onto how the brain represents social rank to guide socially appropriate behaviour within a dominance hierarchy. First, we discuss how the brain responds to social status signals. Then, we discuss social approach and avoidance learning mechanisms that we propose could drive rank-appropriate behaviour. Lastly, we discuss how the brain represents memories of individuals (social memory) and how this may support the maintenance of unique individual relationships within a social group. This article is part of the theme issue ‘The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies’.

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Behavioural and physiological plasticity in social hierarchies

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2020.0443 ◽

2022 ◽

Vol 377 (1845) ◽

Cited By ~ 6

Author(s):

T. M. Milewski ◽

W. Lee ◽

F. A. Champagne ◽

J. P. Curley

Keyword(s):

Mate Guarding ◽

Physiological Plasticity ◽

Pecking Order ◽

Territorial Defence ◽

Social Hierarchies ◽

Dominance Hierarchies ◽

Phenotypic Changes ◽

Current State ◽

Altered Gene

Individuals occupying dominant and subordinate positions in social hierarchies exhibit divergent behaviours, physiology and neural functioning. Dominant animals express higher levels of dominance behaviours such as aggression, territorial defence and mate-guarding. Dominants also signal their status via auditory, visual or chemical cues. Moreover, dominant animals typically increase reproductive behaviours and show enhanced spatial and social cognition as well as elevated arousal. These biobehavioural changes increase energetic demands that are met via shifting both energy intake and metabolism and are supported by coordinated changes in physiological systems including the hypothalamic–pituitary–adrenal and hypothalamic–pituitary–gonadal axes as well as altered gene expression and sensitivity of neural circuits that regulate these behaviours. Conversely, subordinate animals inhibit dominance and often reproductive behaviours and exhibit physiological changes adapted to socially stressful contexts. Phenotypic changes in both dominant and subordinate individuals may be beneficial in the short-term but lead to long-term challenges to health. Further, rapid changes in social ranks occur as dominant animals socially ascend or descend and are associated with dynamic modulations in the brain and periphery. In this paper, we provide a broad overview of how behavioural and phenotypic changes associated with social dominance and subordination are expressed in neural and physiological plasticity. This article is part of the theme issue ‘The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies’.

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Social ascent changes cognition, behaviour and physiology in a highly social cichlid fish

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2020.0448 ◽

2022 ◽

Vol 377 (1845) ◽

Author(s):

Kelly J. Wallace ◽

Kavyaa D. Choudhary ◽

Layla A. Kutty ◽

Don H. Le ◽

Matthew T. Lee ◽

...

Keyword(s):

Social Dominance ◽

Cichlid Fish ◽

Principal Component ◽

Dominance Status ◽

Pecking Order ◽

Dominance Hierarchies ◽

Social Community ◽

Current State ◽

Before And After ◽

Astatotilapia Burtoni

When an individual ascends in dominance status within their social community, they often undergo a suite of behavioural, physiological and neuromolecular changes. While these changes have been extensively characterized across a number of species, we know much less about the degree to which these changes in turn influence cognitive processes like associative learning, memory and spatial navigation. Here, we assessed male Astatotilapia burtoni , an African cichlid fish known for its dynamic social dominance hierarchies, in a set of cognitive tasks both before and after a community perturbation in which some individuals ascended in dominance status. We assayed steroid hormone (cortisol, testosterone) levels before and after the community experienced a social perturbation. We found that ascending males changed their physiology and novel object recognition preference during the perturbation, and they subsequently differed in social competence from non-ascenders. Additionally, using a principal component analysis we were able to identify specific cognitive and physiological attributes that appear to predispose certain individuals to ascend in social status once a perturbation occurs. These previously undiscovered relationships between social ascent and cognition further emphasize the broad influence of social dominance on animal decision-making. This article is part of the theme issue ‘The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies’.

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