New, "Chubbier" River Dolphin Species Found in Bolivia

José Orozco in Caracas, Venezuela
for National Geographic News
August 20, 2008
The Bolivian river dolphin is a separate species from the Amazon river dolphin, scientists announced recently.

Thousands of years ago a powerful drought dried up Brazil's Madeira River, causing a "radical separation" as dolphin populations were caught on different sides of the newly created rapids, said researcher Manuel Ruiz-Garcia.

The Madeira split into today's Beni and Mamoré rivers of northeastern Bolivia. (See a Bolivia map.)

"When they separated, [the dolphins] were never again able to return and reproduce," said Ruiz-Garcia, who heads the Molecular Genetics Lab at Javeriana University in Bogotá, Colombia.

"Thus isolated, the Bolivian river dolphin, Inia boliviensis, eventually developed," he said.

The announcement was made at a recent conservation workshop in Santa Cruz de la Sierra in Bolivia.

Genetic Differences

Ruiz-Garcia took DNA samples from 40 river dolphins from Bolivia and 56 from Colombia by extracting tissue from their tail muscles.

A limited comparison of the DNA revealed significant genetic differences between the two river-dolphin populations.

This led Ruiz-Garcia to initially estimate that the species separated five to six million years ago.

But after comparing 32 more genes from DNA in another 40 Bolivian dolphins and about 60 Colombian and Peruvian dolphins, he concluded that the separation happened much sooner—about 100,000 to 500,000 years ago.

"Bolivian dolphins are totally different molecularly from other dolphins," Ruiz-Garcia said. "After being split up, they accumulated mutations and formed a new species."

(Get a genetics overview.)

Bolivian river dolphins—especially females—also look different from their Amazon relatives.

In contrast to Amazon river dolphins, which are considered "pink," the members of this new species are a pale gray. They also have more teeth, smaller heads, and smaller bodies.

Ruiz-Garcia also considers the Bolivian species to be chubbier and rounder.

The latest genetic studies on the newly declared species allow "a very clear reconstruction of evolutionary history," said Fernando Trujillo, scientific director of Colombia's Fundación Omacha and the leader of South America's first river-dolphin census in 2007.

The River Dolphin Monitoring initiative for South America counted 3,188 river dolphins along 2,232 miles (3,593 kilometers) of the Amazon and Orinoco rivers and their tributaries. (See video of dolphins spotted during the survey.)


The Bolivian river dolphin population may include as many as 25,000 individuals, making the mammal "very abundant," Ruiz-Garcia said.

And unlike the havoc wrought on its relatives by fishers on Brazilian rivers, Bolivia's newfound dolphin can roam safely through pristine freshwater channels.

Yet the mammal still remains vulnerable to environmental disruptions, experts say.

"They're very vulnerable predators," said Paul Van Damme, a researcher for Faunagua, a Bolivian organization that monitors dolphins. "So if fish are affected, they're the first to feel the effects."

For example, if a river fills with mercury, dolphins that eat contaminated fish consume the accumulated metal.

"The dolphins are a reflection of the entire aquatic system," Van Damme said.

(Related: "Last River Porpoises Dying in Polluted Yangtze" [April 23, 2008].)

The animal's greatest threat comes from a Brazilian dam that could raise the water level, alter the river flow, or divert the migration of fish, experts say.

A water-level rise could allow dolphins from both sides of the rapids to move back and forth again for the first time in over a hundred thousand years, Ruiz-Garcia said.

But such a reunion would soon turn tragic, he added.

"The Amazon river dolphin could compete against the Bolivian river dolphin for food, and perhaps bring about its extinction."

A new regional network of 18 scientists have created a conservation plan, which includes economic activities such as dolphin-watching ecotours.

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