An international team of researchers led by scientists at the University of Bristol has been found to create the largest known multi-level alliance network outside of humans. These cross-group alliances make it easier for men to get a scarce resource. In order to reconstruct the structure of alliances between 121 adult male Indo-Pacific bottlenose dolphins at Shark Bay in Western Australia, the researchers, along with collaborators from the Universities of Zurich and Massachusetts, examined association and consortship data. Today, the Proceedings of the National Academy of Sciences published their findings (PNAS).
In Shark Bay, male dolphins group together in first-order alliances of two to three males to cooperate in pursuing mating relationships with specific females. Second-order coalitions are made up of four to fourteen unrelated males who fight for access to female dolphins. Third-order coalitions are made up of second-order coalitions that work together.
Dr. Stephanie King, co-lead author and Associate Professor at the School of Biological Sciences at the University of Bristol, said: “Cooperation amongst allies is common in human societies and one of the defining characteristics of our success. It was once thought that only our species was capable of forming strategic, cooperative ties at various social levels, such as global trade or military alliances.
We’ve shown that male bottlenose dolphins alliance network are the largest multilevel alliance network outside of humans. We’ve also shown that cooperative relationships between groups, not just alliance size, allow males to spend more time with females, which increases their chances of having healthy offspring.
“We show that the duration over which these teams of male dolphins consort females is dependent upon being well-connected with third-order allies; that is, social ties between alliances lead to long-term benefits for these males,” said Dr. Simon Allen, Senior Lecturer at Bristol’s School of Biological Sciences and an author of the study.
The emergence of pair bonds and male parental care were considered to be two further characteristics that set humans apart from our common ancestor with chimpanzees and were necessary for intergroup cooperation in humans. In contrast, intergroup alliances can form from a social and mating system that is more chimpanzee-like, according to the study’s co-author, Richard Connor, a professor emeritus at the University of Massachusetts who is now associated with Florida International University. Dr. King led the study team.
The team will celebrate the 40th anniversary of the start of Shark Bay dolphin research in 1982 and the 30th anniversary of their discovery of two levels of male alliance formation in 1992, which was also published in The Proceedings of the National Academy of Sciences. In 2022, they will write about the importance of the third level, or intergroup alliances, in dolphins.
Professor Dr. Michael Krützen, who led the study and is the Director of the Anthropology Institute at the University of Zurich, said, “Our study shows that you can learn a lot about the evolution of traits that were once thought to be unique to humans by looking at other highly social, large-brained taxa.”
Dr. King’s research shows that dolphins alliance network and societies of nonhuman primates are good ways to study how humans‘ social and mental abilities have changed over time.
