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Jeudi, 03 Novembre 2011 19:15

Sperm Whales Really Do Learn From Each Other

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Sperm Whales Really Do Learn From Each Other

Sperm whales, Earth’s biggest-brained animals, live in far-flung clans with lifestyles so different and vocalizations so complex that it’s natural to think they have culture.

But is that really true? Might sperm whales simply be following genetic instructions? Could their “culture” really be a set of instinctive, mechanical imperatives?

Researchers led by Hal Whitehead of Dalhousie University and Luke Rendell of Scotland’s St. Andrews University, two of the world’s foremost sperm whale biologists, have asked just this question.

Their findings: Yes, sperm whale culture really is culture. And how.

“As far as we know, these are the largest cultures on Earth, aside from human ethnicities,” said Whitehead. “They may have thousands or tens of thousands of members, covering thousands of kilometers of ocean.”

In a study published Oct. 21 in Behavior Genetics, Whitehead and Rendell analyzed sound recordings and skin samples from 194 sperm whales in the southwest Pacific Ocean.

The whales belonged to three “vocal clans,” each possessing a distinctively different repertoire of the Morse code-like clicks used by sperm whales to communicate. Were these dialects biologically determined, the whales would have overlapped genetically as well as vocally — but that’s not what the researchers found.

Instead, whales from different clans are often genetically similar. They’re not identical, but there’s no sign of genetic differences large enough to explain clan differences. These aren’t just vocal: Each clan also differs in hunting patterns, reproductive rates and parenting habits.

“If the differences were genetic, this would make the differences more traditionally biological. We’d have two different subspecies,” said Whitehead. “It’s culture, not genetics.”

The researchers also looked at whether geography might play a role, with each clan responding to local environments. But that doesn’t seem to be a factor: Clans can occupy vast and overlapping swaths of ocean, not a little unlike indigenous human tribes in pre-colonial North America.

“This is like a situation that happens more rarely with humans, where you have several ethnic groups living in the same area but maintaining their identity,” Whitehead said.

In future research, Whitehead and Rendell hope to learn how sperm whale culture passes from generation to generation and between families.

The findings could influence conservation efforts, highlighting the importance of preserving threatened whale cultures. More fundamentally, they affect how people think of cetaceans — not just sperm whales, which are fortunate enough to have been studied by Whitehead and collaborators for decades, but all those species that remain unknown.

“If differences are cultural, we’re getting into the border between biology and anthropology,” said Whitehead. “We’re infringing on some of the traits that some people think are unique to humans.”

Citation: “Can Genetic Differences Explain Vocal Dialect Variation in Sperm Whales, Physetermacrocephalus?” By Luke Rendell, Sarah L. Mesnick, Merel L. Dalebout, Jessica Burtenshaw and Hal Whitehead. Behavior Genetics, Oct. 21, 2011

Image: Ocean Alliance

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