Hyena mothers transmit their social networks to their young

Using 27 years of detailed data on the social interactions of hyenas, a team led by Penn biologists defined a model of social media inheritance and its implications for social structure, rank, and survival.

Hyenas are a very social species, living in groups of up to a hundred. But within their clans, there is order: a specific matrilineal hierarchy governs societies of this species where females are dominant over males.

While researchers have intensively studied the social structure of hyenas and other animals, it is only recently that scientists have started to study how this structure appears. A new study by Penn biologists, which draws on 27 years of detailed observations of the social behavior of hyenas collected by researchers at Michigan State University, lifts the veil on how social order is created.

Their results show that hyenas inherit social networks from their mothers, so their social relationships resemble those of their mother. However, descendants of higher-ranking individuals more faithfully mimic their mother’s interactions, ending up with social networks that are more like their mother’s than descendants of women lower on the clan social scale. The team reported their findings in the newspaper Science.

“We knew that the social structure of hyenas is based in part on rank in the agonistic hierarchy, which we know is inherited from mothers,” says Erol Akçay, study co-author and associate professor at Penn’s School of Arts & Sciences. “But what we found, that affiliate or friendly interactions are also inherited, was not shown.”

“This is a very simple social inheritance process that we are showing works very, very well,” says Amiyaal Ilany, senior lecturer at Bar-Ilan University in Israel. “People born to a higher rank are more precise in their inheritance, and they have good reason to do so. This corresponds well to what we already know about rank inheritance. There are very strict rules about where you stand in the hierarchy if you are a hyena.

The work is based on a theoretical model of social network inheritance developed in 2016 by Akçay and Ilany. According to this simple framework, animals establish their networks through “social inheritance”, or by copying the behaviors of their mothers. The model fits well with real-world social media snapshots from not only hyenas, but also three other social species: bottlenose dolphins, rock hyrax, and sleeping lizards.

In the new work, the team aimed to refine their model to better understand the intricacies of social inheritance in hyenas. They were fortunate to have a strong data set collected by Akçay and Ilany’s co-author, Michigan State University zoologist Kay Holekamp, ​​consisting of 27 years of detailed accounting of social interactions. of a clan.

“We realized that we could use this dataset to directly test our model, to see if social ties are inherited or not,” Akçay explains.

Field biologists in Holekamp’s research group had meticulously followed how hyenas in a clan interacted, including who spent time with whom as well as each member’s social rank. To do this, the researchers spent months getting to know each member of the clan by sight.

“They are there all year round, every day, identifying individuals by their specific spot patterns and other characteristics,” says Ilany.

These observations allowed Akçay, Ilany and Holekamp to map the social networks of hyenas according to the individuals who spent time together.

“This use of proximity to follow social media is not possible with humans, because two strangers can randomly enter an elevator together,” says Ilany. “But with hyenas, if an individual comes within a few feet of another, it suggests that they have a social bond.”

With this picture of each individual’s social affiliations in hand, the researchers compared the social networks of mothers to their offspring. “We have developed a new metric to measure social inheritance, to track how closely a child’s network reproduces its mother’s network,” Akçay explains.

Small hyenas stay close to their mothers for the first two years of their lives, so the networks of mothers and their offspring were quite similar initially. However, the researchers noticed that even though the young people stopped spending so much time near their mothers, they still maintained quite similar networks, especially for the girls, who generally remain members of the clan for life. “We have data in some cases showing that the network similarity between dams and offspring, especially female offspring, was still very high after about six years,” says Ilany. “You might not see your mom that often, or she might even have passed away, but you still have similar friends. “

This trend was particularly strong for senior mothers, for whom the social heritage was the strongest in the group.

“It’s pretty intuitive because things like that also happen in human society,” Akçay says. “It happens so much that we take it for granted. We inherit social ties, and a lot of social science research shows that this has a huge influence on people’s life trajectories.

Children of lower-ranking mothers were less likely to replicate their mothers’ social networks, perhaps trying to compensate for their more humble origins by associating with a wider variety of individuals.

There is no genetic inheritance of rank or close associates in this species, so according to Holekamp, ​​one of the most remarkable things about the phenomenon documented here is that the relationships of young people with close associates from their mothers are all learned very early in life. One explanation of why social media inheritance works better for high rank hyenas than lower rank hyenas may be that lower rank females tend to fend for themselves more often to avoid competition with them. hyenas of higher rank, so that their young have less learning. opportunities that cubs of high ranking females.

Mother-child couples with more similar social networks also lived longer, the team found. This effect on survival may be due to the fact that children who spend more time with their mothers and thereby reproduce their social networks receive increased care.

Social rank also had an effect on survival and reproductive success.

“Rank is super important,” Akçay says. “If you are born to a lower-ranking mother, you are less likely to survive and reproduce.”

The researchers note that the inheritance of social networks likely contributes to the stability of a group and also has implications for how behaviors are learned and disseminated in groups.

The study also highlights the influence of factors other than genetics on key evolutionary outcomes, including reproductive success and overall survival. “A lot of things that are assumed to be genetically determined by default can depend on environmental and social processes,” Ilany explains.

Reference: “Rank-dependent social inheritance determines the structure of the social network in spotted hyenas” by Amiyaal Ilany, Kay E. Holekamp and Erol Akçay, July 16, 2021, Science.
DOI: 10.1126 / science.abc1966

Erol Akçay is Associate Professor of Biology in the School of Arts & Sciences at the University of Pennsylvania.

Amiyaal Ilany is a senior lecturer at the Mina and Everard Goodman Faculty of Life Sciences at Bar-Ilan University and did a postdoctoral fellowship working with Akçay at Penn.

Kay Holekamp is Professor of Zoology at Michigan State University.

The research was funded by the Israel Science Foundation (grants 244/19 and 245/19), the US Army Research Bureau (grant W911NF-17-1-0017), the Binational Israeli-American Science Foundation (grants 2015088 and 2019156) and National Science Foundation (grants 1853934 and 1755089).