Hanging Around With Lemurs, The Planet's Most Primitive Primates

In June, the USC College anthropologist had just returned from a monthlong trip to Madagascar, an island nation off Africa’s east coast. It’s the only place on Earth where lemurs, the assistant professor’s chosen subjects, exist in their natural habitat.

“You have to go literally to the other side of the planet to study them in the field,” Yamashita said of the small primates native to Madagascar.

These furry mammals sport long limbs and large, haunting eyes that earned them their name, derived from the Latin, “spirits of the night.”

Madagascar’s geographic isolation has allowed lemurs to thrive and evolve. The 85 species of lemurs there fill a range of niches across the island’s varied landscapes and climates. However, most species are classified as endangered by the World Conservation Union. Their scarcity adds a sense of urgency to the research done by Yamashita and her peers.

“These are among the rarest primates on the planet,” she said. “We want to get as much information as we can while we can.”

An avid reader since her youth, Yamashita recalls her fascination with evolution as a teen in Arkansas. This interest led her to undergraduate and then advanced study in biological anthropology. Working with her mentor, Marian Dagosto, as a graduate student in 1990 at Northwestern University, she took her first trip to Madagascar to observe lemurs. She has been hooked ever since.

But then, to segue from an early interest in evolution to a career studying Madagascar’s unique fauna makes perfect sense. Scientists consider lemurs to be the closest living relatives of the ancient common ancestor of apes, monkeys and human beings. This has led some to wonder whether these prosimians can provide a view into our own biological origins.

“They’re the most primitive primates,” Yamashita said. “Of course, time hasn’t stood still for them. They’ve also evolved during the 65 million years since primates first began evolving.

“So you have to take (their relation to the common primate ancestor) with a huge grain of salt. You kind of put your blinders on and go, ‘OK, if I’m interested in reconstructing what that ancestor might have been, it might look something like a lemur.’ ”

Yamashita specializes in examining elements of the animals’ diet. She’s a functional morphologist by trade, meaning she concentrates on the relationship between form and function. Her research puts particular focus on the shape and workings of the lemur teeth and jaws, and the physical properties and nutrition of their food. After all, what’s more basic than food?

“Diet plays such a huge role in just about everything having to do with an animal,” Yamashita said. “This is the animal’s job, to find the food and eat it.”

She and her colleagues Chia Tan of the center for Conservation and Research for Endangered Species at the San Diego Zoo and Chris Vinyard of the Northeastern Ohio Universities College of Medicine currently are investigating a trio of lemur species that primarily feed on the same type of bamboo.

This arrangement surprised Yamashita and her collaborators, who would expect one of the lemur species to outcompete its fellow bamboo gourmands. They also wondered how these lemurs, the smallest of which is no larger than a kitten, could handle the hard work of breaking through the plant’s tough exterior to reach its edible growing portions.

While the study is still in progress, it seems that the lemur groups may avoid competition in part by divvying the resource – with different species eating different parts of the plant. As for little jaws vs. big bamboo, the team has noted that the largest bamboo lemurs, who top out at around 6 pounds, employ a very long, labor-intensive approach to dining, aided by surprisingly strong jaw muscles.

“Their little jaws can’t get completely around the bamboo,” Yamashita said. “So they gnaw at it and start a little hole in the bamboo with their canine teeth. Then they lick it, they start peeling the bamboo down till they’ve exposed it. They just poke a hole in it basically and then strip it down.

“They are constantly applying force. They’re sort of overbuilt (in their jaw) to compensate for that (constant exertion).”

And there’s another mystery: The bamboo in question contains high levels of cyanide in its growing parts, a natural defense against hungry herbivores. Somehow, the lemurs show no ill effect, despite taking in a side order of poison with their meals.

“The million-dollar question is, ‘How are these animals able to tolerate it or neutralize it?’ ” Yamashita said.

Her team performed preliminary tests indicating that the cyanide actually passes through the lemurs’ bloodstream, a tantalizing clue that they plan to follow up on in a separate study with a physiologist.

Of course, collecting data in a distant locale yields its own complications. Yamashita and her colleagues have come up with a few sharp ideas to do their science on the spot.

For instance, to determine whether cyanide was passing through the bamboo-eating lemurs’ blood, the team tested the animals’ excreta using chemically treated paper strips. They expected to find cyanide in the animals’ solid waste, indicating that it was evacuated from their digestive tract without reaching their blood. Instead, the tests detected cyanide in the lemur urine, a sign that the poison had passed through the bloodstream, liver and kidney.

In another instance, Yamashita and her colleagues stimulated the jaw muscles of tranquilized lemurs with tiny electrodes and measured bite strength using portable equipment – the first time tests of this type were conducted in the field.

“Basically we brought the lab into the field,” Yamashita said.

Her home base at USC recently relocated: In 2006, she joined the College’s anthropology department from the Keck School of Medicine of USC’s cell and neurobiology department, where she taught anatomy. While Yamashita speaks highly of her students and colleagues at Keck, the switch simply made sense. She feels more at home as one of a number of primate experts at USC College, where she can easily pursue scholarly conversations outside her field.

“I grew up in an anthropology department,” she said. “And then, my field is very interdisciplinary. I’ve consulted chemists in the chemistry department, biologists in the molecular and computational group, people in anthropology.

“To me that’s very valuable, having that face-to-face interaction with people. You need to be able to bump into people and just talk to them. That’s been a huge asset.”

While Yamashita notes that her specialty in lemurs has long been a cocktail-party conversation killer, it seems that in recent years, American pop culture – or maybe just America’s kids, and therefore their parents – have caught up with her.

The cast of Dreamworks’ 2005 animated film Madagascar included funnyman Sacha Baron Cohen voicing a lemur king, and the PBS children’s program Zoboomafoo features a Coquerel’s sifaka (a medium-sized lemur) as its eponymous lead. Nowadays, mentioning “lemur” or “Madagascar” no longer elicits a blank look, she said.

“It’s kind of cool that people know what these lemurs are,” Yamashita said, “that they don’t live anywhere but on this island and that they’re special animals.”

That’s something Yamashita has known for a long time.

A slide show of Lemurs is available at: http://www.usc.edu/schools/college/multimedia/2007/10/lemur/10.html