Monitoring ‘monkey’ molars

Caren B. Les, caren.les@photonics.com

How do you study chimp tooth development in the wild without disturbing the chimpanzees’ behavior? It may not be an age-old anthropological question, but it’s important nonetheless. Understanding dental development in chimps, our closest genetic relatives, could shed light on the evolution of human development.

Harvard University researchers teamed up with wildlife photographers to capture detailed photos of the mouths of individual chimps in Uganda’s Kibale National Park for nearly two years, allowing the researchers to track when the chimps’ molars erupted, and to correlate that information with their behavior.

The high-resolution digital nature photography that they used as a minimally invasive research tool was the most innovative feature of the project, according to wildlife photographer Andrew B. Bernard. The photographers took pictures with DSLR cameras from afar.

“All photos of the wild chimps were taken opportunistically, meaning there was no manipulation of the animals in any way to generate the desired pose,” said photographer Ronan M. Donovan, who would wait patiently for a yawn or a session of play when the juveniles were most likely to open their mouths enough to reveal their molars.

High-resolution digital nature photography was used as a minimally invasive research tool to study dental development in chimpanzees. The photo shows the eruption of the chimp Azania’s early first molars (M1s). She was 3.1 years old at the time. Courtesy of Andrew Bernard.

The processed photos showed that tooth development and weaning in the chimps are not as closely related as once thought. Earlier studies suggested that young primates were weaned shortly after they cut their first molars, but these were based on less-precise data from captive animals, which grow dramatically faster than wild animals, or from skeletal remains in the wild, which are difficult to identify and age.

The new study found that the chimps continued to nurse as much as before, if not more, after their first molars erupted, in addition to eating more solid food. “They were showing adultlike feeding patterns while continuing to suckle, which was unexpected,” said professor Tanya M. Smith.

“Basically, the goals for the tooth pictures were to make it very clear which teeth were present, how far above the gumline they had erupted, and highlighting any protein staining on the gum which might indicate a tooth about to erupt,” Bernard said.

The researchers are planning future studies to better understand why the chimps continue to nurse after their molars develop.

The investigation is described in Proceedings of the National Academy of Sciences (doi: 10.1073/pnas.1218746110).