DOLPHINS form cliques based on their skills, scientists have found, suggesting they could be the only non-human mammals to indulge in elite societies.
Wild bottlenose dolphins bond over their use of tools, with distinct cliques and classes forming over decades as a result of their skills, scientists have found.
The communities, which have been compared with societies such as the Bullingdon Club in humans, mean the aquatic animals share their knowledge only with those in their own circle, passing it down the family line.
The findings mean the traits of “inclusive inheritability” and culture are no longer considered exclusive to human beings.
Observing wild dolphins in Shark Bay, Australia, researchers from Georgetown University used hunting tools as a marker of dolphin societal habits.
Noticing some dolphins in the area used a sponge to protect their beaks while hunting, they attempted to discover why the practice had not spread.
They found the useful tool had first been used by a single dolphin nicknamed “Sponging Eve”, after she scrape her nose while foraging for food in rough sand.
To solve the problem, she broke off a piece of sea sponge to protect her, going on to teach the behaviour to her offsping.
But two decades later, knowledge of the tool had not spread among the whole dolphin population in the area.
Scientists observed 36 spongers and 69 non-spongers in the area over a 22 year period, taking careful note of their relationships.
They found: “Spongers were more cliquish, had more sponger associates and stronger bonds with each other than with non-spongers.
“Like humans who preferentially associate with others who share their subculture, tool-using dolphins prefer others like themselves, strongly suggesting that sponge tool-use is a cultural behaviour.”
This tendency to associate with those most like themselves is, scientists believe, a “critical role in human (sub)cultures”, and “may be true for dolphin society as well”.
Writing in the journal Nature Communications, a team led by Janet Mann reported: “To date, no material subcultures have been identified outside of humans.
“Recently, many biologists are moving beyond genetic inheritance to examine the processes involved in inclusive heritability, which includes culture.
“We sometimes think that traits such as culture are exclusively human, but a growing body of literature proves otherwise.”
Remarkably, researchers believe the cliques are formed for social reasons rather than practical, saying: “As sponging is a solitary behaviour, affiliation between spongers would not be based on collective foraging, but rather on identifying other individuals as spongers”
“We suggest that spongers also share in-group identity, but affiliation is a consequence of similarity in the socially learned trait, a scenario that resonates with human culture,” they said.
“Spongers were more cliquish, had more sponger associates and stronger bonds with each other than with non-spongers.
The study also found the behaviour was stronger in females, who were better at maintaining alliances, noting: “Once sponging behaviour is established, female spongers formed clear cliques.”
Although in-group identity has been noted in other animals, such as killer whales and budgerigars, the dolphin sub-cultures are believes to be the result of socially-learned behaviour rather than inate traits.