Fish phishing attack explained!

Many individuals engage in what social psychologists call “third-party punishment.” We may enforce social codes, even laws, related to marriage, sex, sexuality, vice and property. A classic example is a good Samaritan who ignores personal risk to chase a purse-snatcher. Third-party punishment is so common that evolutionary psychologists suspect that it has genetic roots. Because punishment takes effort and can spark retaliation, it can only have evolved if it benefits the punisher: it can help the punisher reproduce (a direct benefit), or help the community survive (an indirect benefit). Although the roots of human third-party punishment may have nothing to do with evolution, evolutionary psychologists often assume that its major benefit is indirect: I promote social stability by chasing a purse-snatcher. In stable society, I can have more children. Hence in evolutionary terms, chasing a purse-snatcher has indirect benefits. But in a study published this week, researchers found that third-party punishment directly benefits the punisher, at least when said punisher is a “cleaner” fish. Cleaner fish eat parasites housed on larger fish, called “clients.” The relationship is classic symbiosis: the cleaner gets food, while the client stays healthy. In the blue-streaked wrasse Labroides dimidiatus under study, males and females clean in pairs. Occasionally, a female cleaner switches from eating parasites to the more delectable mucus, a sticky goo that protects the client from infection. (We sure swear to skirt slimy, sophomoric silliness and subsequently stick to the science.)

Your cheatin’ heart

Behavioral ecologists call this “cheating” because it breaks the symbiosis and harms the client. Redouan Bshary of the University of Neuchatel in Switzerland studies the wrasse in the Red Sea. He says a client typically swims into a “cleaning station” for about 20 seconds, where a male and female wrasse eat parasites from its exterior. When the female cheats, the client tends to get annoyed and swim to another cleaning station – unless the male wrasse darts at the female to keep her in line. That’s third-party punishment. To test the situation in the lab, first author Nichola Raihani, a post-doctoral fellow at the London Zoological Society, smeared a Plexiglas plate with prawn meal or the less palatable fish flakes. When the females ate the prawn goop, the lab-keepers removed the plate and both fish confronted the sad sight of an empty menu. When males responded aggressively to female cheating, the females were less likely to cheat again, reinforcing the notion that punishment would sustain the symbiosis and get him more food.

Is punishment beautiful?

Even though males were not directly harmed by the cheating, they directly benefited from the punishment, the authors wrote. “The establishment of self-serving third-party punishment in response to personal losses may be a key step toward third-party punishment without current involvement, as in humans.” Scientists have observed punishment among other animals, says Katherine Cronin, a post-doctoral psychology research fellow who studies cooperation among monkeys at the University of Wisconsin-Madison. “Dominant rhesus monkeys might lash out at subordinates who didn’t properly alert them to food,” Cronin wrote us, “and female cowbirds (a species that lays eggs in other birds’ nests to be reared by hosts) may seek out and destroy the eggs of hosts who have previously destroyed cowbird eggs in a surprisingly mafia-like fashion.” Nonetheless, Cronin says, “careful, experimental demonstration of punishment in animals has been rare and requires creative experimental designs like the one employed by Raihani and colleagues.” Cronin notes that cleaner fish are cooperative. “The strongest examples of punishment might not come from the most cognitively complex animals, but rather from the ones that rely most heavily on cooperation to survive.”

Sexual politics, fish-style

Exactly how does the male cleaner benefit from chasing misbehaving females? In most cases, we’d assume that keeping the food source (the client) around would constitute an evolutionary advantage because better-fed males can have more baby fishies, but we must remember that blue streaked wrasses are hermaphrodites. They begin reproducing as females, but females that grow large enough can turn into males. Males can control this conversion, and avoid having another competitor for food, females and territory, by acting aggressively toward females, Bshary says. “If you remove the male, within two days, the female will show male behavior, and within a month, can release sperm that can fertilize eggs.” And thus a male has an incentive to control the largest female in his harem, Bshary adds. “Typically the male tries to control her through aggression so she will not change sex. This is likely to be the main reason why the male responds aggressively to the female.”

What’s the human impact?

Whether the benefit is retaining food, a mate, or both, the study could shed light on puzzling human behaviors, says Raihani. “Until now, most studies on third party punishment have tended to assume it stems from a group-level benefit.” A group-level evolutionary explanation for a crime-fighting good Samaritan would say that living in a crime-free society enables all people, including the Samaritan, to have more children. An individual-level explanation might suggest that the crime-fighting hero could gain social status, and therefore have a better choice of mates. In the fish study, Raihani says, “We are trying to emphasize that you can get what looks like group-level behavior that evolves by individual selection.” One final note, in case you thought the study is “just about fish.” The females are not the only fish who cheat, Raihani says. “Males cheat slightly more than females in this pair cleaning interaction, but females never punish males, because they are so much smaller. So the males can have their cake and eat it too.” Sound familiar?