See a dolphin swimming through the water and you’re not just looking at a sleek and playful marine creature, you’re also seeing an animal with culture.
Indeed, dolphin culture has recently been spotted off the coast of Australia, says new research from a group of international marine biologists studying bottlenose dolphins.
However, this dolphin culture isn’t fancy cocktail parties, visits to art galleries, or listening to contemporary jazz. It’s wearing sea sponges.
This use of sea sponges is first description of potential culture—a skill or tradition that is passed down without the involvement of genetics—in a marine mammal and places dolphins in a select group of animals (basically human and primates) that do the same.
“Over the last five or seven years there has been quite a debate over whether it [dolphin culture] exists,” says Lars Bejder, from Dalhousie University and one of the authors of the research. “This is probably now the best documented case in a wild cetacean…which is comparable to chimpanzees and non-human primates that also use tools,” he says.
The behavior originally puzzled people. Back in 1960s, fisherman noticed some dolphins in Shark Bay, Western Australia, had taken to wearing sea sponges on their beaks (rostrum), says Bejder. When biologists heard about it they had to go investigate, unsure what the reports meant. Over the years, it’s become apparent that the dolphins seem to use sponges during foraging in the coral for fish.
“It’s very peculiar,” says Bejder, “and the theory is that they use it as a protective shield to scare fish and not get cut up by rocks.”
Sponging, as the researchers call the behavior, is passed on from mother to daughter. About 15 mothers and 7 offspring have been seen sponging in Shark Bay over the years. However, the behavior is largely seen only in females and appears to have recently passed down from a single mother, which the researchers have dubbed “Sponging Eve.”
Bejder, lead author Michael Krützen, and their colleagues, think sponging is a form of culture and not just the simple use of a tool (other animals, like birds, use tools but this behavior is passed through genes). They came to this conclusion by excluding other possibilities, namely that sponging is due to the environment or genetics.
An environmental explanation didn’t pan out because numerous other dolphins in the area don’t use sponges, suggesting that nothing is unique to Shark Bay environment, says Bejder, who participated in the project as part of his Ph.D.
To examine if sponging is genetic and potentially passes on through instinct, the researchers also took mitochondrial DNA from 185 dolphins, of which 13 were adult spongers. They then set about comparing patterns in this DNA, or haplotypes, against 10 different explanations for how a sponging gene might be inherited.
For example, if a sponging gene was on the X chromosome and expressed dominantly only in females, you’d expected only to see female spongers. But, at least one male sponger has been observed by the group, negating this pattern of inheritance. The nine other genetic explanations also don’t appear to fit, the results of which are published in PNAS on June 21, 2005.
“We took the three different scenarios [environment, genetics, or culture] and could tick everything off except culture,” says Bejder, “it’s a very exciting result.”
However, critics caution that whether the dolphins are using sponges as tools is still not clear, since its only been inferred by sound recordings and surface behavior so far. More work therefore waits before sponging is labeled a genuine form of culture by all.
Nevertheless, these curious dolphins remind us that culture is not merely a human trait, highlighting our often forgotten connection to the animal kingdom.