"We believe that the marine sponge (which the dolphin breaks off and wears) acts as a kind of glove to protective their sensitive rostra," said marine biologist Michael Krützen of the University of Zurich, who worked at the University of New South Wales in Australia during the study, which he led.
"That probing (of the sea floor) might disturb fish that hide in the sand, which would then be easy targets for the dolphins."
Material culture involves tool-based traits acquired through social learning from select members of the same species. It only has been identified a handful of times in the nonhuman animal kingdom. Chimpanzees appear to have material culture, based on observations of them using tools, such as makeshift stone hammers and anvils to crack nuts, as do orangutans.
To determine if dolphins also possess behavioral traits that can vary culturally, Krützen and his team analyzed DNA taken from known dolphin spongers located at Shark Bay, Western Australia. They focused on DNA to see if there was a genetic explanation for the fact that only 13 dolphins within this particular population appear to use sponges as foraging tools.
The scientists studied the 10 possible modes of inheritance, such as through mitochondrial DNA that comes from mothers, and determined whether these methods could apply to the sponging dolphins. The researchers were able to rule out genetic inheritance because the documented spongers consist of 12 females and one male.
Mitochondrial DNA, for example, would pass down to both sons and daughters, but females mostly engage in sponging. The single male sponger, however, suggested that a female-only chromosome, even a recessive one, is not at work. Krützen believes mothers teaching their offspring is the only other possible explanation for the sponge glove usage.
