Wild-caught chimpanzees, who were orphaned and imported from Africa in their early infancy, exhibit an impaired social behaviour also as adults. So far long-term effects of early traumatic experiences on social behaviour were known only for humans and socially isolated chimpanzees. An Austrian-Dutch research team led by Elfriede Kalcher-Sommersguter and Jorg Massen published these results in the scientific journal Scientific Reports.

Between 1950 and 1980 thousands of chimpanzee infants were wild-caught in West-Africa and exported to Europe, Japan, and the USA, where these chimpanzees have been used in biomedical research. But also many zoos comprise wild-caught chimpanzees: the so-called founder populations.

The new study shows that chimpanzees, who were maternally deprived within their first two years of life, were restricted in their social grooming behaviour even decades later. Social grooming is highly important for the establishment and maintenance of social relationships within groups of chimpanzees. "The orphaned chimpanzees had a lower number of partners they groomed and were less active than were chimpanzees reared by their mothers," says Elfriede Kalcher-Sommersguter of the University of Graz.

These deficits in social grooming are not only found in chimpanzees that were kept singly caged for decades in a biomedical laboratory, before being re-socialised, but also in individuals, who, after being orphaned, grew up in social groups in a zoo. "The severity of the effects of early maternal loss on later social relationships becomes evident by the fact that we found deficits even in chimpanzees that have lived in social groups for up to 40 years now," reports Jorg Massen of the University of Vienna.