Planet Earth

The Punishment Must Fit the Crime---Even for Hermaphroditic, Mucus-Eating Fish

DiscoblogBy Joseph CastroJun 15, 2011 8:33 PM

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Bluestreak cleaner wrasses servicing a "client."

Our legal system was built on the idea that different crimes warrant different punishments. Aggravated assault will snag you less jail time then, say, premeditated murder. And with no small degree of hubris, many of us believe that we’re the only animals on the planet to implement such a discerning system. But scientists have now learned that a species of fish also punish delinquents according to the severity of their crimes

. Starting life as females, bluestreak cleaner wrasse band together to clean off parasites and dead tissue from bigger fish, including sharks. At some point, the largest wrasse in a group, which typically has about 16 members, will change sex

, become harem master, and reproduce with the others. Yet while they normally feed on parasites, wrasse females actually prefer something a bit tastier

: their clients’ mucus. However, a misplaced mucus nibble can annoy the client and thereby drive off the group’s food source, so males chase and bite any females caught misbehaving. Last year, scientists saw that punished females seem to fall back in line.

A new study has found that the severity of the punishment scales with the misdeed. Nichola Raihani of the ZSL Institute of Zoology in London and her team set up a lab experiment with captive wrasse pairs (one male, one female). They presented the fish with Plexiglas plates---i.e. “clients”---bearing two pieces of prawn and either four or eight pieces of fish flakes. The researchers allowed the fish to eat as many flakes as they pleased, but took the plate away if the wrasse touched the prawn (which they love). As it turns out, males chased females longer if they lost plates with more flakes. Moreover, females that suffered harsher punishments were less likely to eat prawn again when the researchers presented a second plate. “Harsher punishment makes them cooperate more,” said Raihani (via New Scientist

). But the issue is more nuanced than that. Raihani believes that male wrasses may be reprimanding gluttonous females partly to ensure that they don’t grow large enough to morph into rival males. In the experiments, males dished out more severe punishments to females of comparable size to them. So, while we can no longer pride ourselves in being the only species on the planet with a complex legal system, at least we can say we don’t generally punish people for being large. (via New Scientist

)

Image: Wikimedia Commons/Nhobgood

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