Bottlenose dolphins form multi-level alliances to find mates — the largest known network outside of humans, according to a new study. Bottlenose dolphins are social creatures, usually traveling in a pod of 12 or more, even though they do strike out on their own from time to time.
Researchers from the University of Bristol, the University of Zurich and the University of Massachusetts surveyed 121 adult male dolphins in West Australia Shark Bay. They found that male bottlenose dolphins form a three-tier hierarchical alliance to form short-term mating relationships with females. The first tier is usually a group of two to three dolphins that pursue individual female dolphins.
The second tier consists of four to 14 unrelated dolphins. They would work together against other male second tier alliances for access to females. The third tier involved multiple alliances working together against other alliances.
“Cooperation between allies is widespread in human societies and one of the hallmarks of our success,” says lead author Stephanie King in a press release. “Our capacity to build strategic, cooperative relationships at multiple social levels, such as trade or military alliances both nationally and internationally, was once thought unique to our species.”
King went on to explain that “not only have we shown that male bottlenose dolphins form the largest known multi-level alliance network outside humans, but that cooperative relationships between groups, rather than simply alliance size, allows males to spend more time with females, thereby increasing their reproductive success.”
Researchers found that the amount of time male dolphins spend with female dolphins is dependent on how well-connected they are with third-tier alliances.
Group cooperation in humans was once thought to be one of the unique features that separates humans from common ancestors like the chimpanzee — along with male parenting and pair bond evolution.
“However, our results show that intergroup alliances can emerge without these features, from a social and mating system that is more chimpanzee-like,” says co-author Richard Connor in a press release.
“Our work highlights that dolphin societies, as well as those of nonhuman primates, are valuable model systems for understanding human social and cognitive evolution,” concludes King in a press release.