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Tool use a family tradition in dolphin clan, researchers say

It’s well known that chimpanzees and orangutans use tools. Scientists have recently come to define this activity as animal “culture” because it is transmitted through generations, and takes different forms in different animal groups. 

Now, researchers say the same should be said of dolphins. 

However, theirs might not be an equal-opportunity culture: “sponging” seems to be almost exclusively a female job.

It in fact appears to be a cultural behavior passed from mother to daughter, said the researchers, led by Michael Krützen of the Anthropological Institute and Museum at the University of Zurich, Switzerland.

They described the findings in a paper in the early online edition of the Proceedings of the National Academy of Sciences, a research journal, this week. 

The spongers are a group of wild dolphins in Shark Bay, Australia. Krützen and colleagues proposed that because almost all are related, they likely descend from one “sponging Eve” who invented the technique. 

It is not clear why so few males do it, as they spend as much time with their mothers as females do, the researchers added.

The scientists analyzed DNA from 13 spongers, only one of which was male, and 172 non-spongers. Bottlenose dolphins in Shark Bay have previously been spotted used nearly a dozen different tactics for food foraging, though none of the other methods involve tools.

Sponging has been seen in 15 of 141 known mothers in the Shark Bay bottlenose dolphin population, the researchers wrote.

They rejected two alternative explanations for the sponging that wouldn’t involve a tradition or culture: a genetic, and a so-called ecological explanation.

The genetic explanation proposes that sponging is due to a “sponging gene” or genes, rather than because of tradition or learning. 

This is unlikely, the researchers said, because because genes tend to be passed down in specific patterns, depending among other things on which chromosomes they are in. None of the known patterns matched the documented one for sponging, in which mostly females, but at least one male, engaged in the activity.

The ecological explanation would state that particular features of the dolphins’ environment are, by themselves, enough to stimulate sponging. This is also improbable because both spongers and non-spongers shared the same feeding and foraging areas, the researchers reported.

The rejection of both the genetic and ecological explanations leaves only one, cultural transmission, they argued.

“A behavioral trait is considered to vary culturally if it is acquired through social learning” and is “transmitted repeatedly within or between generations,” the researchers wrote. “Bottlenose dolphins are highly imitative and capable of social learning, both in the wild and in captivity.”

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