Study argues 'winner-winner' behaviour may shape animal hierarchies
|Indian jumping ants police their nest mate (center) to stop |
her rise in the hierarchy [Credit: Clint Penick]
The researchers began by examining the behaviours and social hierarchy of the well-studied Indian jumping ant (Harpegnathos saltator). When an H. saltator colony's queen dies, the female workers engage in ritual fights to establish dominance. While these battles can be fierce, they rarely result in physical injury to the workers. Ultimately, a group of approximately 10 workers will establish dominance and become a cadre of worker queens or "gamergates."
A social hierarchy like that seen with H. saltator's gamergates is called a shared dominance hierarchy. Most of other ant societies establish despotic hierarchies or linear hierarchies. In a despotic hierarchy, one individual is dominant and all other individuals share the same subordinate status. In a linear hierarchy, there is a clear pecking order: there is a dominant alpha, a beta who is dominant over all but the alpha, a gamma who is dominant over all but the alpha and beta, and so on.
|Three behaviours used to establish a shared dominance hierarchy |
in Indian jumping ant colonies [Credit: Clint Penick]
"We were curious as to whether dueling results in a winner and a loser, or if it is a winner-winner interaction that allows workers to express aggression without requiring a loser," says Jurgen Liebig, an associate professor at Arizona State University who is senior author on the study. Penick adds that dueling may be like, "a couple of football players psyching each other up before a game."
To explore this question, the researchers created a computer model that allowed them to manipulate all three behaviours in order to see how the behaviours affected the social structure of a colony.
When biting was present, but policing and dueling were absent, the model resulted in a linear hierarchy. When biting and strong policing were present, the model resulted in a despotic hierarchy with a single dominant individual. It was only when biting, policing and winner-winner dueling were all present that the model resulted in a shared dominance hierarchy.
"We see examples of all three types of social hierarchies in various ant species, but we also see them throughout the animal kingdom - and we know that shared dominance hierarchies can be found in animal societies from lions to dolphins," Penick says. "Higher cognition certainly plays a role in shaping the societies of many vertebrates, but we think the presence or absence of winner-winner behaviours may be an important factor in determining the nature of dominance hierarchies for a wide variety of species."
Author: Matt Shipman | Source: North Carolina State University [April 14, 2016]