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All in the Big, Hairy Family

23 March 2004 (All day)
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Blood brother. DNA samples isolated from gorilla feces (inset) suggest that neighboring groups of western gorilla are closely related.

Humans are distressingly prone to conflicts, a behavior we seem to share with our primate cousins. When groups of chimpanzees or gorillas cross paths, violent quarrels are frequent and sometimes deadly. Recent observations of the elusive western gorilla, however, have turned up an exception to that pattern: Some groups mingle surprisingly peacefully. Now a DNA analysis of 65 gorillas in 14 groups suggests the friendly interactions may in fact be family reunions.

Brenda Bradley and Linda Vigilant of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and their colleagues used DNA analysis to piece together the genetic relationships among gorillas living in the border region straddling the Central African Republic and the Republic of the Congo. The area is home to western gorillas, which are more numerous than the extremely endangered mountain gorillas in East Africa but are also more mysterious. Their home in the dense forests of Central Africa make it much more difficult to track and observe them, and only a handful of groups have habituated to the presence of researchers.

Bradley, with help from local trackers, spent 3 months collecting hair and fecal samples from gorilla nests in the forest. Each morning, the group would identify gorilla trails and then track them back to their nesting site. There, the team would collect hair and fecal samples for DNA analysis, using the size of the droppings to estimate the age of each individual. Back in the lab, the DNA samples suggested that neighboring groups were often led by males that were related to each other, either as half-siblings, siblings, or father-son pairs.

Although the DNA data are from groups that haven't been directly observed, the researchers suspect that their findings might help explain one puzzle of western gorilla behavior. Researchers have observed a variety of reactions when groups cross each others' paths. Some groups tend to fight, but others seem to get along just fine. Bradley and Vigilant propose that genetics might set the tone for these encounters; related silverbacks might form a sort of network that encourages peaceful interactions between neighboring groups, they suggest in the 23 March issue of Current Biology.

The use of DNA analysis is a powerful tool to help primatologists refine their ideas about how relatedness influences interactions between animals, says primatologist John Mitani of the University of Michigan, Ann Arbor. However, he says, until researchers have DNA information from groups they have observed directly, "it's a bit premature" to draw strong conclusions.

Related sites
Max Planck Institute for Evolutionary Anthropology, Primatology Department
The Primatology Department's Molecular Genetics Laboratory
General information about gorillas
Information about gorilla conservation

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