The death of the mother is a traumatic event for young species where they provide long-term care, such as long-lived mammals, including humans. Now scientists have found that wild orphaned chimps can recover from this stress.
The long-term study, published in the journal eLife, shows that the loss of the mother is stressful for wild immature chimpanzees that are orphans but only for the first two years.
The research is led by the Max Planck Institute for Evolutionary Anthropology in Leipzig and the Institute of Cognitive Sciences of the National Center for Scientific Research in Lyon; For 19 years, scientists investigated the short-term and long-term effects of mother loss on the stress of orphaned wild chimpanzees.
The death of the mother is a traumatic event. Orphaned mammals are known to die earlier and have fewer offspring compared to non-orphans, but how these losses occur is still debated.
Clinical studies in humans and animals in captivity show that individuals whose mothers die when they are young are exposed to chronic stress throughout their lives.
However, this chronic stress, which has harmful consequences for health, can be reduced or even eliminated if orphans - in the case of humans - are placed in foster families young enough.
Now this work shows that wild immature orphaned chimps are highly stressed, especially when orphaned at a young age.
However, orphans who lost their mother later or as adults were no more stressed than other individuals whose mother was still alive.
Our findings contrast with human studies and show that young orphaned chimpanzees recover over time from the initial loss of their mother, which is very stressful, argues Roman Wittig, director of the Taï Chimpanzee Project.
These chimpanzees often care for or adopt orphans, can carry them, share their food and nest at night or protect them from aggression, according to Witting, who nevertheless points out that it remains to be seen whether orphaned chimps recover from stress thanks to the support offered by other chimpanzees.
The stress that orphaned chimpanzees experience compared to non-orphans does not directly explain their shorter lifespan and fewer offspring, but it may have an effect on other important factors such as growth during critical periods of development," he explains by her part Catherine Crockford.
The next step is to figure out what it is that mothers provide their young that helps them get ahead of orphaned chimps. It may be that the mother's presence represents a nutritional gain or a social advantage, such as cushioning the aggressions of others, or a mixture of both, according to Crockford.