How eating too much turns female cleaner fish into males
Humans mete out punishment to those who cheat. And the strength of the punishment depends on the severity of the cheating. But if you thought that this is only a human characteristic, think again. Bluestreak cleaner wrasses (Labroides dimidiatus) are defined by what they eat. Although these fish are born female, the biggest eater transforms into the dominant male, punishing the smaller fish that cheat and end up eating not only the parasites of their client fish but also the flesh. But new international research, presented in the journal Proceedings of the Royal Society B, sheds new light on what happens when the female fish overeat. Much to the dismay of the dominant male, the female who partakes in too much food can become so large that she may transform into a rival male. Researchers led by the Institute of Zoology at the Zoological Society London (ZSL) in the United Kingdom have discovered that male fish are sensitive to the size of their female partners. These fish live in groups, what experts call a harem consisting of up to 16 females for 1 dominant male. The male will typically hook up with the largest female fish to carry out cleaning duties. 'Our research shows that male cleaner fish are sensitive to their female partner's size,' explains lead author Dr Nichola Raihani of ZSL. 'One reason for keeping a cheating female in check may be to stop her eating too much and then challenging his position as the dominant male on the reef.' Cleaner fish live on coral reefs throughout the tropical Indo-Pacific region. The study also found that the male cleaner fish can tell apart what constitutes a low or high-value meal, and will not hesitate to punish the female more severely if she 'drives off' a high-value client. So how does the female fish react? She will offer better service to high-value clients. The researchers point out that it is the first non-human example of where punishment fits the crime, leading the wrongdoer to modify their behaviour based on the potential penalties. According to the researchers, cleaner fish face a problem similar to a 'Prisoner's Dilemma' (scenarios of where cooperation and trust may or may not win over self-interest), when they perform pairwise inspections of joint clients. Only one of the pair will get the benefit associated with cheating (biting the client) while the cost (client departure) is shared between both partners. 'Cleaner fish and humans may not share many physical traits, but cleaner fish punish cheating individuals, just as we punish people who step outside of the law,' Dr Raihani explains. 'In both situations, harsher punishment may serve as a stronger deterrent against future crimes.' Writing in the study, the authors say: 'Despite the benefits of cheating, cleaners apparently find a cooperative solution to this dilemma, largely because females behave more cooperatively during pairwise than during solitary inspections. This increase in female cooperativeness arises because males punish females that cheat and cause joint clients to leave. Males punish females by aggressively chasing them following model client removal.' Do females punish males? No, they don't. The next step for the researchers is to determine how cleaner fish will assess how market forces affect the service quality that cleaner fish provide to client species. Experts from the University of Zurich and the Université de Neuchâtel in Switzerland, and the University of Queensland in Australia contributed to this study.For more information, please visit: Zoological Society London (ZSL): http://www.zsl.org/ Proceedings of the Royal Society B: http://rspb.royalsocietypublishing.org/
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Australia, Switzerland, United Kingdom