It's a cutthroat world out there, and the male cuttlefish is not above using sneaky tactics to fool rivals and buy more time to woo potential mates. But what causes a seemingly mild-mannered trickster to morph into the aquatic equivalent of a street fighter? The answer can be found in the footage below, the first of its kind to capture male cuttlefish going mano-a-mano to secure the future of their progeny in the wild.

Our story begins innocently enough: boy meets girl … and then they proceed to get it on. "This male just kind of appeared right next to my left side and rested next to a clump of algae on the sea floor," recalls co-author Justine Allen who captured the entire episode in the Aegean Sea off the coast of Turkey. "The female was a few meters in front. Out of nowhere he just swam up, grabbed her, and they mated in the head-to-head position."

Typically, the male common cuttlefish (Sepia officinalis) will remain by its mate's side for a while to make sure she uses his sperm to fertilize her eggs. Unfortunately, post-coital bliss was not on the cards for this pair, as a male rival showed up minutes later and tried to break them up.

As can be seen in the video below, what ensued was a fascinating display of macho posturing, cuttlefish-style: raising stiff arms, dilating w-shaped pupils, darkening faces and flashing the zebra-like bands on their skin.

"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," explains Allen. "A lot of their fighting is done through visual signals. Most of these battles are actually these beautiful, stunning skin displays. It's a vicious war of colors."

The stand-off, which lasted around four minutes, involved three bouts of escalating aggression. At first, it looked like the first male was going to have to concede defeat. In the first two rounds, despite attempts to guard and then reclaim his position, the intruder managed to keep him away with well-timed aggressive gestures, including swipes with his fourth arm.

However just when all seemed lost, the first male was finally given the trigger that he needed to level up and go nuclear on his rival when the latter tried to force the female to mate with him (for anyone who's wondering, she wasn't interested).

The consort male rushed back into the fray and grabbed the intruder, twisting him around in a barrel roll three times – the fiercest move in the cuttlefish arsenal – and biting him. Meanwhile, the female decided she wanted no part of this and slipped away, leaving the two to settle the score between themselves.

The fight ended moments later with the intruder fleeing the scene and a happy ending for the first male, who was found swimming with his mate moments later.

"Male 1 wins the whole thing because we saw him with the female later, and that's really what matters," says Allen. "It's who ends up with her in the end."

Researcher Justine Allen with a cuttlefish(Credit: Derya Akkaynak)

Macquarie University biologist Culum Brown, who was not part of the study, says the interaction between the males during their four-minute stand-off is "reasonably standard."

"It's great footage that's for sure," he tells New Atlas. "These guys are reasonably single-minded at mating time so … we generally separate our cuttlefish into pairs once they bond in captivity to prevent these aggressive interactions. The striping is typical of the species and intensifies during aggressive interactions. Notice how the approaching male in all occasions attempts to make himself look larger than he really is. This is also pretty standard for aggressive interactions."

That said, what stood out for him was how quickly the fight escalated. "That means the males are of similar size and both fancied their chance at winning," he says. "I'm also willing to bet that given the first male had already mated, he had a higher vested interest in the female which explains why he came back for more after losing the initial encounter."

For study co-author and marine biologist Roger Hanlon, this encounter is also fascinating in that it fits the "mutual assessment" model of game theory, meaning that individuals evaluate their opponents' as well as their own abilities before deciding whether to fight or flee. This requires more smarts than making decisions based on one's strength alone, which is not surprising given that scientists consider cuttlefish to be one of the smartest invertebrates around.

The video below documents the cuttlefish throw-down.

The study is published in American Naturalist.

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