Spotted hyenas live in clans, sometimes numbering as many as 100 individuals. Within a clan, the status of each animal is determined by its standing in the social hierarchy.
Female hyenas are dominant to males and the leader of each clan is an alpha female. High-ranking individuals tend to have better rates of survival and reproduction.
While researchers understand the dynamics of hyena social hierarchies quite well, they have never uncovered how the status of a mother is passed on to her offspring, when no genetics is involved in this inheritance.
In a recent study by biologists from the University of Pennsylvania, it was established that young hyenas not only copy their mother’s behavior, but they also inherit their mother’s network of “friends.”
“We knew that the social structure of hyenas is based in part on one’s rank in the agonistic hierarchy, which we know is inherited from mothers,” said study co-author Professor Erol Akçay. “But what we found, that affiliative, or friendly interactions, are also inherited, hadn’t been shown.”
The study was based on 27 years of observations on hyena social behavior, collected by study co-author Kay Holekamp of Michigan State University. In particular, the proximity of an individual to others was used to map out social networks among clan members.
“With hyenas, if one individual gets within a few meters of another, that suggests they have a social connection,” explained Amiyaal Ilany, a senior lecturer at Israel’s Bar-Ilan University.
Once researchers had a picture of each individual’s social connections, they could compare the networks of mothers and offspring. Clearly, while a cub is young it spends most of its time with its mother and both of them interact with the same individuals. But even when cubs grow older and spend less time with their mothers, they maintain the same social connections.
This pattern was particularly strong for high-ranking mothers and their female cubs, where network similarity was still very high, even when cubs were six years old, according to Ilany.
In Holekamp’s opinion, hyena cubs form relationships with their mothers’ close allies early in life, thus cementing their own social standing and rank for the duration of their adult lives.
This study illustrates that genes are not the only factors that can influence evolutionary processes, such as reproductive success and survival.
“A lot of things that are considered by default to be genetically determined may depend on environmental and social processes,” said Ilany.
The study is published in the journal Science.