Emotion

gobies, which obtain most of their food via cleaning. Some obligate cleaners, such as L. bicolor and L. phthirophagus, mostly eat fish mucus and so are not considered as cooperative as the rest. But even the supposedly very cooperative ones, like L. dimidiatus, will eat mucus when they can get it. Most cleaner fish, however, are facultative cleaners which means they do not rely solely on cleaning for food. Facultative cleaners tend to be juveniles, such as some butterfly and angel fishes and many wrasses. Some wrasse clean fish as juveniles but eat corals as adults. What are the latest findings on cleaner fish? The evolutionary stability of cleaning mutualism has been recently examined. Cleaning interactions resemble the Prisoner's Dilemma: predators can cheat by eating the cleaner, while cleaners can cheat by eating mucus; hence both partners may cooperate or defect. But the solution is not a form of reciprocity, because the predator terminates the game if it cheats and so tit-for-tat-like strategies are not possible. Hence, L. dimidiatus are virtually unconditionally cooperative towards predators in the wild, though less so in the laboratory. L. dimidiatus also provide much tactile stimulation (rubbing with their pelvic fins) to predators, apparently to reduce conflicts from occurring. Non-predatory clients, however, use different control mechanisms: clients that can access only one cleaning station rely on aggression to control cheating cleaners, whereas those that can access more than one station flee and switch to another station. Oddly, the risk of aggression from predators toward nearby prey fish is greatly reduced as a by-product of cleaner fish presence and the tactile stimulation of predators by cleaner fish, suggesting cleaning stations act as safe havens from predator aggression. Probably no surprise to most snorkelers, a recent study confirmed that cleaner fish have evolved some of the most conspicuous combinations of colors and patterns in the marine environment: they tend to be yellow or blue, aspects that are in stark contrast to their stripes and make them stand out from the reef background; blue in cleaners also attracts more clients to cleaning stations. Many new species of cleaner fishes have also been reported, even one of a shark apparently functioning as a 'cleaner' with a 'client' fish scraping its body against the shark's body; in this case there appears to be no benefit to the cleaner. Intriguingly, a recent molecular analysis suggests that cleaning in Labroides spp. evolved …