Dolphins have captured our imaginations for decades due to their acrobatics, funny and charismatic faces and intelligence. Now, researchers are gaining even more insight into their complex social networks.
A paper published yesterday in Proceedings of the National Academy of Sciences (PNAS) claims that male bottlenose dolphins form the largest known multi-level alliance network outside of humans. Humans form alliances for various strategic reasons (economic, social, political, etc.) and dolphins appear to form similar complex strategic relationships with each other. The international team of scientists say these cooperative relationships between groups increase male access to a contested resource: female mates.
Researchers at the University of Bristol, the University of Zurich and the University of Massachusetts looked at association and community (or short-term mating relationships) data to model the structure of alliances among 121 adult male Indo-Pacific bottlenose dolphins in Shark Bay. The bay is a UNESCO World Heritage Site in the Gascoyne region of Western Australia and has a number of “outstanding natural features, including one of the largest and most diverse seagrass beds in the world,” according to UNESCO- s.
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The team finds that male bottlenose dolphins form first-order alliances of two to three males to cooperatively pursue these short-term mating relationships with individual females. Second-order alliances of four to 14 unrelated males compete with other groups for access to female dolphins. Third-order alliances occur between cooperative second-order alliances.
In the late 1980s, the team had previously discovered that adult male dolphins swam in pairs and trios, cooperating to ‘herd’ single females that were ready to conceive. They first saw two teams collaborate to attack another group of dolphins, showing that just like humans, dolphins have cliques within larger alliances.
“Cooperation between allies is widespread in human societies and one of the hallmarks of our success,” co-author Stephanie King, associate professor of biological sciences at the University of Bristol, said in a press release. “Our capacity to build strategic, cooperative relationships at multiple societal levels, such as trade or military alliances, both nationally and internationally, was once thought to be unique to our species. Not only have we shown that male dolphins form the largest known network of multilevel alliances outside of humans, but that cooperative relationships between groups, rather than simply alliance size, allow males to spend more time with females, thereby increasing their reproductive success.
Research published in 2021 showed that male dolphins responded strongly to allies who had repeatedly helped them in the past, even if they were not currently close friends. In addition, they did not respond strongly to men who had not consistently helped in the past, even if they were currently friends. This indicates that these dolphins form social concepts of ‘team membership’, organizing allies according to a shared history of cooperation.
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Intergroup cooperation in humans was thought to be unique and dependent on the evolution of pair bonds and male parental care. These are two more traits that distinguish humans from our common ancestor with chimpanzees. “Our results show that intergroup alliances can emerge without these features, from a social and mating system more akin to chimpanzees,” said co-author Richard Connor, professor emeritus at the University of Massachusetts, who is now affiliated with the International University of Florida.
This research builds on exactly 40 years of studying Shark Bay dolphins and the 30th anniversary of the team publishing their discovery of two levels of male alliance formation.
“It is rare that non-primate research is conducted by an anthropology department,” Michael Krützen, a study author and head of the Institute of Anthropology at the University of Zurich, said in the release. “But our study shows that important insights about the evolution of characteristics previously thought to be uniquely human can be gained by examining other highly social, large-brained taxa.”