Lemur mothers share parenting responsibilities

Yale researchers spent six years studying cooperative child-rearing in ruffled lemurs in Madagascar’s Ranomafana National Park.
Yale researchers spent six years studying cooperative child-rearing in ruffled lemurs in Madagascar’s Ranomafana National Park. Photo by Andrea Baden.

Lemurs and humans might seem like starkly different creatures, but a recent study by Yale researchers shows that they raise their young in similar ways.

Published on Aug. 6 in the journal Behavioral Ecology and Sociobiology, the study finds that ruffed lemurs in Madagascar participate in cooperative child-rearing, putting their young in nests together and sharing the duties of motherhood. Molecular anthropology postdoctoral research associate Andrea Baden, first author of the study, said this type of cooperative infant care has previously been seen only in humans.

From 2005 to 2010, Baden and her team followed a community of black-and-white ruffed lemurs in Madagascar’s Ranomafana National Park. They noticed that many baby lemurs were grouped together into kindergartens, and those that were raised through this cooperative care system had greater survival rates. While only two out of five lemurs with single mothers survived, 13 out of 14 lemurs with cooperative mothers survived.

“It seems like infant survival is driving cooperation, but we don’t know what the approximate mechanisms are,” Baden said.

She said it has been suggested that female adults who share parenting responsibilities have more time away from the nest to hunt, and stronger, well-nourished mothers can then provide more nutrition to their young. These cooperative mothers may have higher milk quality or may be better at protecting the nest from predators, she added.

Even more interesting than the discovery of lemur kindergartens was the finding that genetic relatedness had no impact on whether females would cooperate — some non-kin participated in co-nesting, while some kin did not.

Study co-author Brenda Bradley, an assistant professor of anthropology at Yale, said evolutionary scientists too often assume that the only reason for cooperation in the wild is kin selection, the theory that animals will help their relatives because they want their genes to be passed on to the next generation.

Bradley said this study provides compelling evidence that cooperation is not driven solely by kin selection.

“This was the most surprising result, and it reinforces the idea that we can’t just assume cooperation is kin-based,” Bradley said. “What this study finds is that to cooperate is actually beneficial for the mothers and infants as mutualism.”

She added that this research provides insight into the evolution of day care.

Most people think of day care as uniquely human, but nonhuman primates also participate in day care and reap the benefits of cooperative child-rearing, Bradley said. She added that these findings have important implications for species conservation as well.

The increasing threat of climate change could have an effect on ruffed lemur reproductive patterns, which is something she said she hopes to address in the future, especially given that this species is critically endangered.

Baden has already started working on determining the proximate causes for cooperative child-rearing, which she said will require additional long-term behavioral research.

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