Fierce mating battle between wild cuttlefish

The dramatic encounter was filmed in 2011 by Derya Akkaynak of the University of Haifa and Justine Allen, then a Ph.D. student in the Brown University-Marine Biological Laboratory (MBL) Graduate Program, while diving in the Aegean Sea with Allen's doctoral research advisor, MBL Senior Scientist Roger Hanlon. The team's analysis of the cuttlefish combat, with contributions by Alexandra Schnell of University of Caen, is published this week in American Naturalist.

Hanlon was "ecstatic" when saw the dive footage, he says. Although researchers have studied cuttlefish competition and mating behavior in the lab, observing the complex interactions of male-male fighting and mate guarding in the wild has been elusive.

"This was a totally serendipitous video sequence that I had been searching for nonstop for 20 years," Hanlon says.

The encounter began after Allen and Akkaynak filmed a male and female mating and then swimming together, as the male guarded his mate. Suddenly, a second male cuttlefish interrupted the couple's honeymoon, stealing the female away.

The two males began displaying the bizarre posturing of cuttlefish aggression: raising stiff arms, dilating their w-shaped pupils, and flashing skin colors.

"They have a whole repertoire of behaviors that they use to signal to each other, and we're just barely starting to understand some of them," says Allen, now an adjunct instructor at Brown University. "Most of these battles are actually these beautiful, stunning skin displays. It's a vicious war of colors."

But when the new male tried to mate with the female, things quickly turned physical.

The two male cuttlefish began grappling, spurting ink, until the first male managed to spin the intruder in three rapid barrel rolls. The harassed intruder slipped free and swam off. Soon after, Hanlon filmed the first male successfully reunited with his mate.

Though this encounter documented just one case of cuttlefish fighting, the team's analysis and comparison to lab results suggests that the behavior fits the "mutual assessment" model of game theory: Each individual evaluates his next action based on his opponent's ability and his own ability to prevail, rather than just on his own strength. This is particularly intriguing to Hanlon, as he says mutual assessment requires more cognitive ability.

Hanlon says the analysis through game theory is an important step in studying aggression, which, while widespread in the animal kingdom, remains poorly understood.

"Aggression is a major part of many societal problems, but it's a very touchy subject," Hanlon said. "This field observation and game theory analysis sets up a way to do lab experiments differently. I'm hoping we can put animals in the tank [to study aggression] based on this field assessment."

Link to video: https://doi.org/10.7301/Z0PR7SX4