Among fish, dominance reduces influence

If fish are any guide, subordinate males may actually have more influence on groups than their domineering and aggressive counterparts, according to a new study in the journal Proceedings in the National Academy of Sciences.

The researchers, led by Alex Jordan from Germany’s Max Planck Institute, were interested in the interplay between power, dominance and influence – a theme permeating animal and human populations.

“In many societies, whether animal or human, individuals in positions of power all possess a similar suite of traits,” says Jordan. “They are often loud, aggressive, pushy, and at least in our current political climate, overconfident in their knowledge of specialist matters.”

Gaining positions of power tends to be a competitive process, thus favouring individuals that use aggression and intimidation to get their way.

“But are these powerful individuals most influential?” Jordan asks.

“And if our goal is to create groups and social structures that are responsive to change, and through which new information spreads quickly and effectively, do we really want the most aggressive individuals in powerful positions?”

To explore whether dominant or passive males have more clout, his team turned to a species of cichlid fish, Astatotiliapia burtoni, with strict social hierarchies and domineering males.

“We ask whether it is the colourful dominant males, those who are central in their social networks, are aggressive, and who control resources, that are the most influential,” says Jordan. “Or is it drab, subordinate males who wield the greatest influence, despite being passive, non-territorial, and having little or no control over resources?”

The team, including co-first authors Mariana Rodriguez-Santiago from the University of Texas, US, and Paul Nührenberg, examined how information flows between dominant or subordinate males in two different contexts: habitual social behaviour or a more complex social learning task.

They used machine learning to track the fishes’ movements and behaviour and tease out the fine scale behavioural interactions between all group members to work out who is most influential in each context, and why.

When powerful leaders wielded influence, coercing others into certain behaviours by chasing and pushing them around, it was through aversion.

“Dominant males are indeed most influential in some contexts,” says Jordan; “by chasing and showing aggression to others, they effectively ‘push’ the group away, ‘leading’ through others avoiding them.”

In a more complex, association learning task, group members needed to learn that a coloured light would reward them with food through observing a dominant or subordinate male that already knew the connection.

Given the choice about who to follow, the passive males had the greatest influence.

“In groups with a subordinate male as demonstrator, the group quickly came to a consensus about which light to follow, moving together as a coherent unit to succeed in the task,” Jordan explains.

“With a dominant male as the informant, groups were far slower to reach consensus, if they did at all.”

And although dominant males had central positions in behavioural social networks, interacting frequently with others, others tended to avoid them. They also had low “signal-to-noise” ratios of usefully informative behaviour.

In other words, the dominant males spent much time aggressively chasing others around, while the passive males changed their normal slow speed to swim quickly and decisively towards the right feeder.

The researchers liken this to research showing how aggressive humans impact group performance, and even “toxic leadership”, especially when group function is needed.

“This is similar to a President that tweets incessantly – it is difficult to figure out what information to pay attention to,” says Jordan.

“Subordinate males, in contrast, were more like a certain medical advisor, speaking only when necessary, and whose words therefore carry great weight.”