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Smithsonian Scientists Find Female Coatis Help Offspring of Other Females

Unexpected result challenges understanding of the role of kinship in mammals

May 22, 2012

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    Coati and cubs

When Smithsonian Conservation Biology Institute postdoctoral fellow Ben Hirsch found that juvenile ring-tailed coatis regularly attack stronger, older coatis and often even receive help from adult females, previous studies about how related animals treat one another could not predict his next discovery. Working with the National Zoo’s Genetics Lab to determine how closely the coatis in his study were related, Hirsch found that the juveniles sometimes attacked their own kin and often received help from unrelated adults.

“No previously published model of animal behavior would have predicted that young juvenile coatis should regularly attack and steal food from older relatives,” Hirsch said. “Additionally, the pattern that adult females come to the aid of these non-related juveniles really flies in the face of what we thought. What we have described is a quasi-cooperative behavior that is evidently not kin based.”

Coatis, which range from Columbia to Venezuela down to Uruguay and northern Argentina, are a highly social species related to the raccoon and known for being particularly aggressive, especially when it means access to food. They live in cohesive groups of up to 65 individuals that usually include only a single adult male. Over the course of the three-year study, Hirsch monitored the behavior of 150 individual coatis in four social groups in Iguazu National Park in Argentina. Using genetic data, he found that in 57 percent of the cases in which an adult female helped a juvenile during an aggressive encounter, the female was not the mother of the juvenile.

In addition to aggression, Hirsch and his colleagues compared genetic data to behavioral data to determine how kinship played a role in grooming and association in social networks. Contrary to what Hirsch and his colleagues found with aggression, relatedness seems to play a large role in shaping how coatis associate with and groom one another. The results were published May 18 in PLoSONE.

The question researchers are left with is how do females benefit from protecting unrelated juveniles. While adult females in some species protect juveniles from aggression, the patterns found in coatis appear to be unique among mammals.

“By understanding the factors that shape the evolution of animal societies, we may be able to further understand how and why human societies might have evolved,” Hirsch said.

The International Union for Conservation of Nature lists ring-tailed coatis to be of least concern, though their population is decreasing in some regions as the result of deforestation and hunting. In some urban areas, coatis have adapted to feeding from human refuse, which leads to huge increases in aggression between coatis in these populations.

Visitors to the National Zoo can see three white-nosed coatis, Baby Jack, Petunia and Curly Tail.

In addition to Hirsch, the paper’s other authors are Jesús Maldonado, SCBI research geneticist, and Margaret Stanton in the Department of Biology at Georgetown University.