FLIPPER has joined the elite. Australian bottlenose dolphins have been spotted using tools – and it seems they can also pass on their specialist knowledge to their offspring. This is the first time cultural transmission has been confirmed in a marine mammal.
Lacking hands, dolphins are limited in what they can do with a tool, but the dolphins of Shark Bay, Western Australia, don’t let this trifling fact stop them. Some break marine sponges off the sea floor and wear them over their snouts while foraging (Â鶹´«Ă˝, 19 July 1997, p 23).
“We believe that they use sponges as a kind of glove to protect their sensitive rostrums when they probe for prey,” says Michael Krützen, formerly of the University of New South Wales, Sydney, and now at the University of Zurich, Switzerland. Most sponges are flat, but the dolphins pick conical ones that don’t fall off their snouts. What’s more the spongers are almost all female.
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To discover if tool use was a genetic trait or one culturally transmitted, Krützen’s team analysed DNA from 13 spongers, only one of which was male, and 172 non-spongers. Twelve of the spongers were related, sharing the same mitochondrial DNA type, which is only transmitted from mother to offspring. But by analysing nuclear DNA, the researchers showed that tool using could not be explained by a “gene for sponging” – the trait’s pattern of inheritance just didn’t fit (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0500232102). The researchers conclude that the behaviour is culturally transmitted, presumably by mothers teaching the skills to their offspring, although they have not actually observed this feat in action.
Dolphins in captivity are well known for their exceptional learning abilities, and whale song patterns can be culturally transmitted. But this is the first example of tool use being passed on culturally in a marine mammal, an ability so far only seen in primates and perhaps some birds.
Krützen also has a theory about why males don’t use the sponge. “Males are more interested in forming alliances with other males than sponging,” he says. “They have a different social life than females, and this might restrict them to invest too much time in sponging, which is quite a solitary activity.”
Other tool users
New Caledonian crows
Can bend wire to retrieve food
Burrowing owls
Use dung as bait to trap beetles
Sea otters
Use stones to crack shellfish
Chimpanzees
Use sticks to gather ants; stones to crack nuts
Orang-utans
Use branches to swat insects away
