In Shark Bay, Australia, unrelated bottlenose dolphins have exhibited a remarkable behavior— they have been observed teaching each other a novel way to use a tool. This is a behavior that, until recently, scientists had only witnessed in humans and other great apes. Furthermore, this marks the first known instance of dolphins passing down such knowledge within the same generation, rather than across generations.
The dolphins engage in a practice known as shelling. They chase fish into abandoned giant snail shells lying on the seabed. After that, they bring these shells to the surface and shake them with their noses, removing the water and capturing the fish that escape.
"The fact that shelling is socially transmitted among dolphin peers rather than between mother and child sets an important milestone," senior study author Michael Krutzen said.
In 2007, Krutzen launched a study of Shark Bay's dolphins, identifying more than a thousand individual dolphins over 11 years. During this time, scientists observed shelling 42 times among 19 dolphins. Half of these events occurred after a marine heatwave in 2011, which may have caused a die-off among giant sea snails, leading to more shells on the seafloor.
Because of the length of their study, scientists had very detailed knowledge of the individual dolphins' family histories, ages, sexes and behavior, making it easier for them to study the 19 dolphins that practiced shelling. For instance, they observed that the dolphins that practised shelling hung out with other shellers, so it's likely that they copied from those they spent time with, says study lead author Sonja Wild.
The team knew that environmental factors- specifically, whether shelling dolphins did so simply because they lived in a shell-rich area-could explain this peer-to-peer transmission. A genetic characteristic among a family group was another possible reason.
So the researchers combined their data on the dolphin sightings, as well as genetic and environmental data, into a computer model that proposed various ways shelling could be transmitted between dolphins. The model that supported horizontal (横向的) transmission was the strongest outcome, according to the study.
