You’re a Southeast Asian mangrove crab that answers to Perisesarma eumolpe. Specifically, you’re a very male, very ferocious mangrove crab, despite being about an inch wide. Another male’s shown up and wants to prove how tough he is, so you meet on a mangrove root, lock claws, and tussle. You’ve pushed your opponent around enough to prove yourself superior, but then he looks like he might come back for another round. You’ve got to show him who’s boss. How? You cut a rug. You get your groove on. You shake it to show your rival that there’s more where that came from. For years, scientists had observed male mangrove crabs dancing after a fight over a female. Researchers from the University of Singapore wanted to understand why. Enter crab thunderdome.
The team set up a combat arena and paired crabs randomly. Following 55 percent of these scuffles, the winner performed a taunting victory dance. There’s only one move involved: You point your oversized claw down to the ground and then rub the other claw up and down it quickly—something between the mashed potato and the crustacean equivalent of the universal “jerk off” gesture. The dance may be physically tiring, but it seems to have an emotional impact. Among the fights followed by a victory dance, 65 percent of winners felt sufficiently invigorated to go in for another swipe, while only 35 percent of losers wanted another round. But if there’s no victory dance, the outcome is exactly the opposite: Winners go back in for more only 35 percent of the time, and losers want a rematch 65 percent of the time.
This kind of “signaling behavior” takes place all over the animal kingdom: male greylag geese cackle distinctively after a successful attack, and insects such as the New Zealand tree weta rub their legs together and chirrup after a fight. We obviously have our own kinds of culturally bound victory dances, from the Maori haka to the Korean seungjeonmu to elaborate football end-zone celebrations. The common factor appears to be that they are predominantly conducted by males. No reflection on the researchers themselves, but this latest study might just be the most “bro” science ever: game theory combined with a structured fight club to prove something about male dominance. Somewhere a bunch of mangrove crabs are dancing in approval.