Monday, March 23, 2009

The secret lives of lemurs

Ask any new dad, and he’ll tell you — having a new baby in the house is no picnic.

Anthropology Professor Patricia Whitten recently uncovered evidence that, in communities of the earliest primates, newborns stress out the males. “I’m looking at different aspects of hormones and behavior in wild primates to understand humans better,” says Whitten, who specializes in the links between behavior, biology and reproduction.

Whitten began her career studying wild vervet monkeys in 1977, while she was a Harvard graduate student. She had grown up in a suburb of Chicago and had never even been camping when she headed to a remote reserve in northern Kenya for her solitary fieldwork.

“Months before I left, my mother would send me newspaper clippings with headlines like, ‘Africa Aflame!’ She was so worried,” Whitten recalls.

Whitten, however, enjoyed the adventure. “The reserve was full of lions, wild dogs, elephants and buffalo,” she says. “In the morning on my way to work, I’d pass all these wonderful beasts.”

The vervet monkey troops she observed were spread over varying habitats, from the thick forests along a riverbank to a seasonably drier area where vegetation was sparse. Giving birth right after the rains allowed a mother to indulge in handy meals of acacia seeds. If an infant was born just a few weeks later, however, the mother had to feed on the tiny, clover-like flowers of the acacia — a more labor-intensive task which required her to push away her clinging newborn so she could leap from limb to limb. After three years in the field, Whitten published groundbreaking data that showed the link between ecological factors, social status and reproductive rates in the vervets.

“Timing was important for these females,” she says. “Low-ranking females conceived late and gave birth late.”

In 1989, Whitten joined Emory, where she established a lab that has gained an international reputation for the analysis of steroid levels in fecal samples of wild primates. The data can help reveal all sorts of complex social dramas, from the emotional impact on baboons after a relative is killed by a lion, to the secrets of monkey mating strategies.

In 1998, she began collaborating with Diane Brockman of the University of North Carolina in a study of sifaka lemurs in Madagascar. Lemurs are prosimian primates — believed to be the forerunners of more advanced primates like apes and monkeys.

The sifaka particularly intrigued Whitten, since the females dominate the males. “A female will leap right behind a male while he’s feeding, reach over his shoulder and grab some leaves and start eating them, almost as if she is daring him to move,” Whitten says. “If he’s smart, he won’t.”

In addition to fieldwork, Whitten was responsible for the lab analysis in the sifaka study, along with Emory graduate student Amy Cobden. The study results, published February 25 by the Proceedings of the Royal Society B, found that male sifaka become more anxious during the annual birthing season. Whitten initially thought that the rise in glucocorticoid levels in males could be tied to an environmental factor. She was surprised that the data pointed instead to the presence of a new infant.

Field observations revealed another surprise: male sifaka play a nurturing role with infants, grooming and caring for them. But the correlation between higher stress in males and the birthing season remains a mystery.

One hypothesis is that the males are worried about aggression by males from neighboring groups: Sifaka males roam and visit other groups of sifaka during the birthing season. Sometimes the visitors challenge the dominant male of a group. Occasionally, they will even kill infants.

For Whitten, the complex dramas revealed by the initial study raise more questions. For instance, why do the female sifaka sometimes allow visiting males to hold their newborns? “The females are dominant, so they are choosing which males are trustworthy — but sometimes they don’t seem to be choosing that well,” Whitten says.

While she is continuing to study vervets, the prosimian primates — believed to have originated 65 million years ago — offer her a glimpse further back. “In anthropology, we commonly talk about 1 million years of evolution, or 5 million,” Whitten says. “If we start looking at behavior going back 65 million years, think how much more deeply ingrained that may be.”

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