Tactical toothed whales: Evolution of between-group alliances in a non-human model

Cooperation across social boundaries is ubiquitous in human societies. Indeed, our capacity to build strategic cooperative relationships across social borders, such as trade or military alliances, was thought to be unique to our species. However, there is now evidence for intergroup cooperation in taxonomically diverse groups, spanning ants to wrens and bonobos to dolphins. Researchers have generally focused on between-group conflict, leaving a gap in our understanding of between-group cooperation. This is perhaps surprising given that current global challenges require cooperation on an unprecedented scale, and that understanding the key processes that may promote prosocial and cooperative behaviour has clear societal benefits. Studies on between-group cooperation in non-humans should lead to a deeper understanding of the phenomenon in humans and other animals, which would be of great interest to biologists, anthropologists, psychologists and political scientists, promoting a step-change in our understanding of between-group cooperation. Bottlenose dolphins are an especially promising case for investigation because male dolphins form the largest multilevel alliance network outside humans, where between-group cooperation increases access to a contested resource. Unrelated males from different alliances will help each other gain access to females without obtaining an immediate payoff themselves and with no guarantee of a return. Our multi-decadal study on dolphin cooperation combines long-term behavioural and demography data over the lifetime of individuals with state-of-the-art technology that allows fine-scale, field-based observations and experimental manipulations. In this project, we will critically examine the proximate and ultimate mechanisms that underpin between-group alliances and between-group cooperation, addressing this new frontier through data and experiment. We will use four decades of behavioural data with large-scale social network analyses to examine the ontogeny and stability of between-group alliances. We will test how maternal effects, kinship, behavioural homophily (the tendency of individuals to interact with others who are like them), sociability and ecology all influence between-group alliance formation, as well as the impact of the loss of key allies on cooperative relationships between groups. We will also conduct behavioural follows with drone-mounted video and underwater microphone arrays to quantify the behavioural mechanisms used by individuals as they engage in between-group alliance interactions. Specifically, we will test how physical and vocal processes are used to promote and maintain social bonding and facilitate fission–fusion events between alliances. These behaviours will be mapped onto social network measures and will uncover how variation in behaviour relates to connections between cooperative groups and participation in cooperative tasks. Finally, we will conduct field manipulations to investigate the social cognition underpinning these between-group alliances. Our experience studying dolphin identity signals will inform the design of sound playback experiments with drone-mounted video to test how response to rivals is mediated by the presence of within- and between-group allies, while accounting for demographic and social traits. Cross-species research is crucial to understanding how between-group cooperation evolved. In addition to breakthrough discoveries on between-group cooperation in dolphins, outputs from this project will provide a framework for future work on the mechanisms underpinning between-group cooperation. Such a framework would allow us to identify similarities and differences in the socio-ecology and evolution of intergroup cooperation across taxonomic groups and identify the adaptive significance for cooperation across social borders for different species. The project is therefore of fundamental importance for a holistic understanding of the evolution of between-group cooperation in humans and other animals.