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Here’s another example, unrelated to cannibalism. The reef-inhabiting bluehead wrasse (Thalassoma bifasciatum) is famous for its habit of removing parasites from much larger fish, even entering into their mouths. In this case, however, it’s the removal of a male wrasse from its harem of 30 to 50 females that alters their local environment. Rather than waiting for a new male to arrive, something extraordinary takes place in the harem. Within minutes, one of the females begins exhibiting male-typical behaviors. Relatively quickly, the former female transforms into a male, a form of phenotypic plasticity known in the trade as protogyny. The opposite occurs in protandry, in which individuals begin life as males and transform into females. Examples include the clownfish (Amphiprion), whose behavior could have offered an intriguing alternative resolution to the animated film Finding Nemo.
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