Do dominant monkeys gain more warmth? Number of physical contacts and spatial positions in huddles for male Japanese macaques in relation to dominance rank

Influence of ecological and social factors on huddling behaviour and cluster organisation in Japanese macaques (Macaca fuscata)

Huddling behaviour is present in many animal species. This behaviour involves maintaining close physical contact with conspecifics to minimise heat loss and, in general, reduce energy expenditure. Additionally, this behaviour also facilitates complex social interactions within a population. In Japanese macaques, this behaviour is observed in many populations across Japan, including Shodoshima, where huddling clusters can reach up to 100 individuals in winter. Based on several studies on this species, it appears that huddling, or sarudango in Japanese, is influenced by both meteorological factors and social relationships between individuals. The objective of this study is to understand the determinants that drive the expression (presence or absence) and the organisation (number of individuals and identities) of huddling clusters. Two hypotheses were formulated. The first hypothesis posits that the formation and variations in the size and number of clusters are influenced by meteorological factors, while the second hypothesis suggests that the number and position of individuals within a cluster are related to existing relationships between individuals. To test these, data on the number, size, and individuals composing a cluster were collected, allowing building huddling social networks. Simultaneously, meteorological measurements were taken, along with observations on dominance and grooming interactions between individuals. This allowed us to create several statistical models and social networks for comparison. Our results suggest that the probability for observing huddling is mainly related to solar radiation energy, while variations in number and size could be explained by temperature. Moreover, the organisation within a cluster is not random but reflects relationships between individuals. The ones sharing more grooming and having similar dominance ranks have more probabilities to be in the same huddling cluster.

The Warmth of Sarudango: Modelling the Huddling Behaviour of Japanese Macaques (Macaca fuscata)

Huddling behaviour is observed across various mammalian and avian species. Huddling, a behaviour wherein animals maintain close physical contact with conspecifics for warmth and social bonding, is widely documented among species in cold environments as a crucial thermoregulatory mechanism. Interestingly, on Shodoshima, Japanese macaques form exceptionally large huddling clusters, often exceeding 50 individuals, a significant deviation from the smaller groups observed in other populations (Arashyama, Katsuyama, and Taksakiyama) and climates. This study aims to uncover the mechanisms behind the formation and size of these huddling clusters, proposing that such behaviours can be explained by simple probabilistic rules influenced by environmental conditions, the current cluster size, and individual decisions. Employing a computational model developed in Netlogo, we seek to demonstrate how emergent properties like the formation and dissolution of clusters arise from collective individual actions. We investigate whether the observed differences in huddling behaviour, particularly the larger cluster sizes on Shodoshima compared to those in colder habitats, reflect variations in social tolerance and cohesion. The model incorporates factors such as environmental temperature, cluster size, and individual decision-making, offering insights into the adaptability of social behaviours under environmental pressures. The findings suggest that temperature plays a crucial role in influencing huddling behaviour, with larger clusters forming in colder climates as individuals seek warmth. However, the study also highlights the importance of joining and leaving a cluster in terms of probability in the dynamics of huddling behaviour. We discussed the large clusters on Shodoshima as a result of a combination of environmental factors and a unique social tolerance and cohesion among the macaques. This study contributes to our understanding of complex social phenomena through the lens of self-organisation, illustrating how simple local interactions can give rise to intricate social structures and behaviours.

Neural basis of collective social behavior during environmental challenge

Humans and animals have a remarkable capacity to collectively coordinate their behavior to respond to environmental challenges. However, the underlying neurobiology remains poorly understood. Here, we found that groups of mice self-organize into huddles at cold ambient temperature during the thermal challenge assay. We found that mice make active (self-initiated) and passive (partner-initiated) decisions to enter or exit a huddle. Using microendoscopic calcium imaging, we found that active and passive decisions are encoded distinctly within the dorsomedial prefrontal cortex (dmPFC). Silencing dmPFC activity in some mice reduced their active decision-making, but also induced a compensatory increase in active decisions by non-manipulated partners, conserving the group's overall huddle time. These findings reveal how collective behavior is implemented in neurobiological mechanisms to meet homeostatic needs during environmental challenges.

How feedback and feed-forward mechanisms link determinants of social dominance

In many animal societies, individuals differ consistently in their ability to win agonistic interactions, resulting in dominance hierarchies. These differences arise due to a range of factors that can influence individuals' abilities to win agonistic interactions, spanning from genetically driven traits through to individuals' recent interaction history. Yet, despite a century of study since Schjelderup-Ebbe's seminal paper on social dominance, we still lack a general understanding of how these different factors work together to determine individuals' positions in hierarchies. Here, we first outline five widely studied factors that can influence interaction outcomes: intrinsic attributes, resource value asymmetry, winner-loser effects, dyadic interaction-outcome history and third-party support. A review of the evidence shows that a variety of factors are likely important to interaction outcomes, and thereby individuals' positions in dominance hierarchies, in diverse species. We propose that such factors are unlikely to determine dominance outcomes independently, but rather form part of feedback loops whereby the outcomes of previous agonistic interactions (e.g. access to food) impact factors that might be important in subsequent interactions (e.g. body condition). We provide a conceptual framework that illustrates the multitude potential routes through which such feedbacks can occur, and how the factors that determine the outcomes of dominance interactions are highly intertwined and thus rarely act independently of one another. Further, we generalise our framework to include multi-generational feed-forward mechanisms: how interaction outcomes in one generation can influence the factors determining interaction outcomes in the next generation via a range of parental effects. This general framework describes how interaction outcomes and the factors determining them are linked within generations via feedback loops, and between generations via feed-forward mechanisms. We then highlight methodological approaches that will facilitate the study of feedback loops and dominance dynamics. Lastly, we discuss how our framework could shape future research, including: how feedbacks generate variation in the factors discussed, and how this might be studied experimentally; how the relative importance of different feedback mechanisms varies across timescales; the role of social structure in modulating the effect of feedbacks on hierarchy structure and stability; and the routes of parental influence on the dominance status of offspring. Ultimately, by considering dominance interactions as part of a dynamic feedback system that also feeds forward into subsequent generations, we will understand better the factors that structure dominance hierarchies in animal groups.