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EvolutionEvolution

For Hyenas, Climbing the Social Ladder is Easier with Friends

In these female-dominated clans, the name of the throne-toppling game might just be camaraderie.

ByKatherine J. WuNOVA WondersNOVA Wonders
Coalition photo credit Kate Yoshida.jpg

Two spotted hyenas engage in coalitionary aggression against a third. Coalitions such as this one usually reinforce, but occasionally disrupt, the social hierarchy. Image Credit: Kate Yoshida

For Waffles, the only direction to go was up.

And as the lowest-ranking female in her clan of spotted hyenas (Crocuta crocuta), she had little to lose. Among her peers, Waffles was neither the biggest nor the brawniest; by all accounts, she was—physically speaking—unremarkable.

But to the amazement of Eli Strauss and Kay Holekamp, the Michigan State University evolutionary biologists tracking the hyenas’ behavior, over the course of just a single year, Waffles steadily ascended her group’s hierarchy, unseating high-ranking female after high-ranking female—until, at long last, the former underdog had attained the coveted alpha position.

“She was just so persistent,” Holekamp says. “It was absolutely stunning.”

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The secret to Waffles’ success? According to Strauss and Holekamp’s research, published today in the journal PNAS, Waffles battled her way to the top not by leveraging stature or might, but by arming herself with the most powerful weapon of all: a troupe of loyal comrades at her side. And though her case was extraodinary, Waffles was—by several metrics—far from alone. Even when born into a low station in life, with ironclad alliances to bolster confrontations with higher-ranked individuals, female spotted hyenas can shirk the lottery of birth and clamber atop the social pyramid.

“The quality of this work is outstanding,” says Elizabeth Archie, a behavioral ecologist at the University of Notre Dame who was not involved in the study. “This shows that animals that navigate the social arena can turn a hierarchy on its head.”

This tactic sounds simple, but it was an answer hard won. To arrive at these chummy conclusions, Strauss and Holekamp had to sift through 27 years’ worth of data, tracking over 12,500 aggressive interactions among 249 adult female hyenas in Kenya.

“Such a huge sample size over such a long time is not something we have the luxury of doing in behavioral research very often,” says Suzanne MacDonald, a biologist who studies primate behavior at York University and was not involved in the study. “They’ve gotten data we often theorize about, but can’t often test. It’s awesome.”

Waffles.jpg

This hyena, named Waffles, ascended to become the alpha female of her social group through coalitionary support from her allies. Image Credit: Tracy Montgomery.

It turns out hyena social climbing, even on a small scale, is a relative rarity (making Waffles all the more anomalous). Their hierarchies are actually remarkably stable—perhaps due in part to the fact that, like many primates, spotted hyenas are intelligent, highly adept puzzle solvers capable of cultivating rich social networks. A single spotted hyena can individually recognize each member of a clan of dozens, and will invest this social savvy in allies and adversaries alike.

While many other animals give top billing to individuals with the most prominent or powerful physical attributes—like the seal with the greatest girth, or the bird with the flashiest feathers—spotted hyenas structure their societies like female-centric monarchies. Offspring inherit ranks directly below that of their mothers and above those of their older siblings. In this nepotistic system, might and stature hold little sway, and even small, frail, and sickly individuals can hold dominion over their peers through heritage alone.

This dynastic dictum poses a bit of a puzzle, however. With tantalizing incentives, like better access to food and mates, high up on the social ladder, Holekamp says, you might expect big-bodied individuals to constantly be “beating up weaker, older, more fragile individuals higher up in the hierarchy to improve their position.”

Quite the opposite is true. In fact, only a small fraction of the thousands of encounters Strauss and Holekamp had tracked actually involved a lower-ranking female staging a successful coup d’état (far more actually involved females in the upper echelons reaffirming their dominance).

When these revolutions did occur, however, it wasn’t the females with the hardiest physiques that were overthrowing their superiors—but the ones with the most robust friendships.

In the realm of the hyena, it seemed, the name of the throne-toppling game was camaraderie.

A classic confrontation might go something like this. Two females team up and swagger, shoulder to shoulder, in the direction of their higher-ranking rival, tails bristled and ears cocked, using pure posture to communicate their intent, Strauss says. The hyena on the receiving end would then have a choice to make: reassert her dominance, or yield. If daunted by the pair loping towards her, she might simply hunker down and tuck her tail between her legs—a clear signal of defeat.

In other words, these weren’t necessarily violent mutinies, Strauss says. “When people think of aggression, they think of hair flying and blood and intestines,” he says. “That’s not what’s going on here.”

Occasionally, standoffs did escalate to the point of bodily harm—especially when a high-ranking female decided to stand her ground in the face of a challenge. Despite these risks, though, uprisings appeared to paid dividends: By ascending the social ladder, females and their accomplices boosted their reproductive success. The repercussions of these revolts were even passed on to future generations, who reaped the benefits of their mother’s newly acquired clout.

Although these status switchups weren’t happening on a daily basis, they support the idea that “rank inheritance isn’t a foregone conclusion,” Archie says. “There could be this impression that animals are born with a silver spoon in their mouth and they pass that on. But there’s nuance to that.”

The power of partnership isn’t terribly surprising, says Floria Mora-Kepfer Uy, who studies social behavior in animals at Cornell University and was not involved in the study. Hyenas, like many other social species, thrive on strong social bonds—and the allegiances that allow individuals to clamber up to higher echelons might be the same ones that reinforce the ranks once they’ve resettled. In this way, social currency might form two sides of the same coin: It’s what maintains, and occasionally disrupts, the hyena hierarchy.

Soc snf DSG-copy.jpg

Spotted hyenas have primate-like societies in which individual hyenas form strong social bonds with their preferred partners. Image Credit: David Green. 

“This is all the more reason animals on the bottom need to not kick their friends, but to hold them up,” says Emily Weigel, an evolutionary biologist at the Georgia Institute of Technology who was not involved in the study. “Social environment matters. And it’s shaping evolution way more than we thought.”

What’s more, spotted hyenas are unlikely to bear this congenial mantle alone. Other primates, like macaques and baboons, also inherit status through strict and stable matrilines. Such parallels hint that these “very impressive” results might translate into other species, says Stefano Kaburu, an evolutionary biologist and primatologist at the University of Wolverhampton in the United Kingdom who was not involved in the study.

“I was nodding as I was reading this paper,” MacDonald says. “This makes perfect sense. I was almost salivating, thinking that I should look at my own data with these methods.”

And there’s one other notable primate for whom these conventions might ring true: humans. Differences exist between the two species, of course—but there’s an undeniable familiarity to the idea that coalitions can make or break social standing, Holekamp says.

“Our own societies are largely convention-based,” she says. “My feeling is that, ultimately, it will be wonderful if we can take some of this knowledge and use it to someday make human society more egalitarian.”

But that won’t happen on its own, Holekamp says. “Social inequality, even though it is a highly common characteristic in human and animal societies, can be understood and quantified, and managed,” she says. “If we have the brains to do it.”

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