It takes a village, they say. The same tenet applies, it turns out, to our friend the spotted hyena.
Hyenas are neither dogs nor cats. They are cousins of meerkats and mongooses, of all things. Hyenas exist throughout Africa and Asia and reportedly some still cling on in Israel, though, sadly, massive packs of the carnivorous beasts are a thing of the past in the Holy Land. Nor is the U.S. thronged with hyenas, which died out there almost a million years ago.
Yet now collaboration between an Israeli researcher, Dr. Amiyaal Ilany of Bar-Ilan University with Dr. Erol Akçay of the University of Pennsylvania, working on enormous reams of data created by Kay Holekamp of Michigan University, has shed light on the Hyaenidae social life: for the spotted hyena, social ties are inherited.
Their paper, “Rank-dependent social inheritance determines social network structure in spotted hyenas,” was published Thursday in Science.
Hyena friendship is not genetically inherited, though relative amiability might be. Rather, hyena offspring tend to form relationships with the same hyenas their mothers are friends with – especially at the higher echelons of hyena society within the clan.
It’s pretty much what one would expect in pack animals, and hyenas live in clans that can be 130-strong and more. But there is a twist in their tale.
Hyena social life is matriarchal. Clans are dominated by females, who had once been confused with males or hermaphrodites because their clitoris resembles a penis so large that it would make many a man burst into tears of envy. The female spotted hyena even has faux testicles.
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Yet, like in male-dominated species, lower-ranking hyenas do not do as well as higher-ranking animals. They may not be able to eat their fill and cubs born to a lower-ranking mother are less likely to survive and reproduce, the researchers found. “Rank [in the hyena world] is super important,” says Akçay.
Dominance also passes from mother hyena to cubs – the female cubs, that is. “Itinerant adult males rank last, reduced to submissive outcasts begging for acceptance, food and sex,” as Lucy Cooke memorably wrote on Ideas.Ted.Com.
While one may assume social ties are “inherited” in pack animals, proving it is another matter entirely. The suspicion that friends are “passed down” from mother to child applies to other social species too, including elephants and primates, but reports are isolated and anecdotal.
Akçay and Ilany created a theoretical model suggesting that “social inheritance” – where the kids “inherit” social bonds from their parents, passively or through imitation – could explain the social networks of multiple species. What was missing was hard data, and lots of it.
The team analyzed a vast body of work done by coauthor Kay Holekamp: 73,767 social observations among wild spotted hyenas in Kenya over 27 years. Hard data, and lots of it.
The team showed that, as the model predicted, a process of social inheritance determines how offspring relationships are formed and maintained. “The relationships of offspring with other hyenas are similar to those of their mothers for as long as six years, and the degree of similarity increases with maternal social rank,” they write.
The mechanism by which social bonds are “passed down” remains unclear: the babies could be copycats, imitating the mother; or it could be a passive process.
Nu, so is it a surprise? No. But it is singular proof that social rank can play a critical role in survival.
“We found overwhelming evidence that social connections of offspring are similar to those of the mother. A mother who has social affiliations with another hyena can connect her offspring to that hyena and the two, in turn, will form a social bond,” Ilany explains. “Even after the mother-offspring bond itself weakens dramatically, the offspring still remain connected to their mothers’ friends.”
The truth is that spotted hyenas get a bad rap. They are not filthy, stinking, snarling, malevolent scavengers that persecute other predators to filch their feast of fresh cadaver. They are extremely intelligent, spunky predators – albeit with rather matted fur and objectionable table manners. But they can coordinate and hunt down gigantic animals such as buffalo. Even individual hyenas hunting alone can evince immense grit and bring down large prey by exploiting soft spots and grabbing on to… Never mind.
The bottom line is hyenas are smart, some variants primarily scavenge but some mainly hunt. Some researchers suspect them of relatively advanced communication skills because of the way they manage their day-to-day existence, splitting into sub-groups for the purposes of hunting, fighting, and feeding.
Now the new study shows that the kids of elite hyenas face fewer constraints in picking their friends and surviving. Sound familiar?