(CN) — Of all alliances across the animal kingdom, those formed by bottlenose dolphins are the largest and most resemble humans, new research shows.
The cooperative, multilevel relationships formed among bottlenose dolphins — a species widely known in part because of its ability to be trained by humans, both for show and for military purposes, and whose intelligence may nearly rival or perhaps even surpasses humans — take aim at attracting females.
Male dolphins work together to attract and mate with females, and dolphins who are well-connected socially have better, easier access to mates, scientists found.
Their findings, published today in The Proceedings of the National Academy of Sciences (PNAS), prove that animals can have relationships almost as complex as humans.
“Cooperation between allies is widespread in human societies and one of the hallmarks of our success. 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,” Stephanie King, an associate professor from the University of Bristol’s School of Biological Sciences, and co-lead author on the study, said in a press release.
“Not only have we shown that male bottlenose dolphins form the largest known multilevel 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,” King continued. (Emphasis in the original.)
For the study, researchers analyzed the alliances between 121 adult male Indo-Pacific bottlenose dolphins at Shark Bay in Western Australia.
The team found that male dolphins will band together either in two groups of three, or in four groups of 14 each, and compete with other groups of the same size for the attention of female dolphins.
The availability of female dolphins in an area influences how competitive males are to attract a mate, researchers found. Also, how well-connected a male is will help his chances of winning a mate considerably.
“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 leads to long-term benefits for these males,” Simon Allen of Bristol’s School of Biological Sciences, who contributed to the study, said. (Emphasis in the original.)
Scientists previously believed intergroup cooperation in humans evolved from our common ancestor, chimpanzees and required two features that distinguish humans from chimps: the evolution of pair bonds, and parental care by males. But this new research proves the previous hypothesis was incorrect.
“Our results show that intergroup alliances can emerge without these features [the evolution of pair bonds and parental care by males], from a social and mating system that is more chimpanzee like,” Richard Connor from the University of Massachusetts, who co-authored the paper, said.
Professor Michael Krützen, an author on the study and head of the Anthropology Institute at the University of Zurich said in the press release that it is unusual for an anthropology department to take up animal behavior.
“It is rare for non-primate research to be conducted from an anthropology department, 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,” Krützen said.
Dolphins have long been widely admired for the tight-knit communities they form and respond to, for their nurturing behaviors and ability to be trained. But breakthrough discoveries in recent years into dolphin mating patterns have also shined a light on the complexities and dark side of dolphin mating practices.
Dolphins are polygamous, mating only with the same partner over a series of interactions, or even just one, and then moving on to another mate.
Females typically birth just one calf at a time every three to five years, without the help of a mate, and keep the calf at their side for five years. Gestation takes 12 months.
Male dolphins are sometimes quite romantic in their attempts to attract a partner: singing to her, bringing her gifts, displaying feats of acrobatics, or even fighting other potential suitors to attract the desired mate’s attention.
But other times, male dolphins do not try to win a female’s attraction with romance so much as through the help of their alliances with other males, sometimes working with other dolphins to chase a female down, and sometimes even separating her from her pod by force.
Although the research published today focuses exclusively on male dolphin cooperation in mating, previous studies have shown that female dolphins are also adept at forming alliances, oftentimes to help one another outsmart and escape bands of male dolphins.
King said in the press release that studies of dolphin alliances at Shark Bay will help understand human behavior and how it has developed over time.
“Our work highlights that dolphin societies, as well as those of nonhuman primates, are valuable model systems for understanding human social and cognitive evolution,” he said.
The researchers did not immediately reply to emails asking for additional information.
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