via New Scientist:
Now it turns out that one animal does punish just like a human: the bluestreak cleaner wrasse. But their carefully nuanced punishment of “cheats” is really an elaborate plot to oppress their females.[…]
Bluestreak cleaner wrasse have small home territories called cleaning stations. Each male maintains a harem of around 16 females dotted around his territory, who help him service his clients.[…]
When the female ate a piece of prawn from a plate that had eight fish flakes – thereby depriving the pair of all those fish flakes – the male chased her more than if the plate had only four fish flakes. When a second eight-fish-flake plate was offered, females who had experienced this severe punishment were less likely to eat the prawn.
“Harsher punishment makes them cooperate more,” Raihani says. The males must somehow be judging the seriousness of the females’ crimes and punishing accordingly, something no other non-human animal has ever been seen doing.
The system may sound just, but it is actually systematic sexual oppression.
All bluestreak cleaner wrasse are born female. The largest individual in a given area changes into a male and dominates the remaining females.
That means each male is under constant threat from his attendant females. If one of them manages to grow bigger than him, she can change sex in just two days and potentially take over his territory.
For a female to grow bigger than her male, she needs to eat more than him. So taking chunks out of client fish could work well for her: she gets a particularly nutritious meal, but her partner gets nothing because the client fish leaves in disgust.
Accordingly, Raihani found that males were more likely to dole out harsh punishments if their partners were a similar size to them. Such large females would have been on the cusp of changing sex, so the males controlled their behaviour more strictly.
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