The scale of animal intelligence and social learning still continues to amaze scientists, and no less so in two new studies looking at dolphins and wasps.
The first, published in the journal Current Biology, found that dolphins not only used empty shells as tools to catch fish – the second time tool use has been observed in cetaceans – but that they learn this trick from other dolphins.
It’s very unusual to observe social learning outside the mother-offspring bond, according to senior author of the international study, Michael Krützen, from the University of Zürich, Switzerland.
“If a behaviour is learned from the mother, it is said to spread vertically,” he says. “Horizontal transmission, the spread between adult peers, is much rarer in the animal kingdom.”
During a decade of boat surveys in Shark Bay in Western Australia, the researchers noticed that some dolphins carried empty sea snail shells on their beaks and then vigorously shook them.
At first, they thought it was some kind of play behaviour, says Krützen. “However, when we got close enough … and took some photographs, we could not believe what we saw – there was a fish trapped inside the shell!
“So the dolphins appeared to trap the fishes inside the shell while it was sitting on the ocean floor. They then bring it to the surface and shake it so the fish falls into their mouth.”
Throughout their survey, the team had more than 5000 encounters with dolphin groups and identified more than 1000 different Indo-Pacific bottlenose dolphins (Tursiops aduncus). They saw more than 40 instances of “shelling” by 19 different individuals.
After a marine heatwave around 2011 to 2012, which likely killed many gastropods and left their shells empty, the behaviour seemed to spread as dolphins who knew each other started to catch on.
The team confirmed this was a form of social learning with complex statistical analysis that ruled out other possible mechanisms such as asocial or individual learning, genetic similarity or environmental differences.
Previously, they had found the heatwave negatively impacted the dolphins, so the shelling appears to be a form of shrewd innovation, Krützen notes.
“Given that dolphins are clever inventors, it seems that they might be able to cope with such challenges by switching to a new way of finding food.”
Back on land, wasps use social learning to gauge their likelihood of beating a potential rival in a fight, according to the other study published in the same journal.
Insects mostly seem to learn about others through direct interactions, but Elizabeth Tibbetts, from the University of Michigan, US, wondered if wasps could eavesdrop on fights between potential rivals.
“In nature, I often see two wasps fighting while a group of other wasps observe the fight,” she says. “I wondered how much the observers were learning and remembering about the other fighters.”
Her team staged videotaped fights between Polistes fuscatus wasps in the lab, after marking them with unique colour patterns.
Two at a time, “fighter” wasps were placed in the fighting arena – a small container – while “bystander” wasps watched them through clear partitions. Scores were awarded on an aggression index for behaviours like biting, stinging, grappling and mounting – a form of dominance – during a fight.
Bystander wasps were later paired in the fighting arena with wasps they had and hadn’t observed, and their behaviours were compared between each condition to rule out other possible explanations for different aggression levels.
Results showed bystander wasps were less likely to pick a fight with wasps who were more aggressive and fought more with those that had been the victim of aggression or had initiated very little fighting, demonstrating they had indeed learned from what they saw.
“A wasp could observe that ‘Suzy’ is a tough fighter and easily dominates other wasps,” Tibbetts says. “Later, when the observer wasp interacts with Suzy, she’ll submit without even trying to fight.
“I was completely shocked to find that social eavesdropping has such a huge effect on wasp behaviour. It’s one of the strongest effects I’ve found in twenty years of doing behavioural studies on paper wasps.
“We keep underestimating insects. Insects use their tiny brains to produce surprisingly sophisticated behaviour.”
Natalie Parletta is a freelance science writer based in Adelaide and an adjunct senior research fellow with the University of South Australia.
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