Wrasse Punish Cheaters
The bluestreak cleaner wrasse (Labroides dimidiatus) operates an underwater health spa for larger fish. It advertises its services with bright colours and distinctive dances. When customers arrive, the cleaner eats parasites and dead tissue lurking in any hard-to-reach places. Males and females will sometimes operate a joint business, working together to clean their clients. The clients, in return, dutifully pay the cleaners by not eating them.
That’s the basic idea, but cleaners sometimes violate their contracts. Rather than picking off parasites, they’ll take a bite of the mucus that lines their clients’ skin. That’s an offensive act—it’s like a masseuse having an inappropriate grope between strokes. The affronted client will often leave. That’s particularly bad news if the cleaners are working as a pair because the other fish, who didn’t do anything wrong, still loses out on future parasite meals.
Males don’t take this sort of behaviour lightly. Nichola Raihani from the Zoological Society of London has found that males will punish their female partners by chasing them aggressively, if their mucus-snatching antics cause a client to storm out.
At first glance, the male cleaner wrasse behaves oddly for an animal, in punishing an offender on behalf of a third party, even though he hasn’t been wronged himself. That’s common practice in human societies but much rarer in the animal world. But Raihani’s experiments clearly show that the males are actually doing themselves a favour by punishing females on behalf of a third party. Their act of apparent altruism means they get more food in the long run.