Researchers: Male clownfish morph into aggressive females when mates die

EXETER, England — When we think of clownfish, many of us are reminded of the Disney hit “Finding Nemo.” At the beginning of the film, Nemo’s mother is eaten by a barracuda, while his father survives the ambush. New research finds, however, that should an actual male clownfish’s mate dies, the widower becomes a widow — that is, the male clownfish changes sex entirely and becomes a female.

Marine biologists from CRIOBE (Center for Insular Research and Observatory of the Environment) in France revealed their findings at the University of Exeter after studying the behavioral, physiological, and hormonal changes in clownfish, also known as anemonefish, for years.

New research finds that when female clownfish die, their male mates actually change completely to females to take on the vacant role.

They discovered that when a female clownfish dies, its mate morphs into the opposite gender to take on the role of protecting territory occupied by the species’ group as well as other fish.

“There need to be lots of hormonal changes to become fully female. When the male has changed sex, the largest sub-adult male becomes her new mate with whom she lays eggs,” says co-author of the research, Dr. Suzanne Mills, in a university press release.

In general, clownfish demonstrate a bit of a role reversal for many creatures when it comes to offspring. The females, which keep a lookout for threats to the group, are known to be more fierce than their smaller male counterparts — so much so that they’ll even attack exponentially larger sharks passing through. Meanwhile, male clownfish tend to stay home and tend to the eggs, even fanning them while the females keep a lookout for predators and go on the offensive for their families when they feel threatened.

But should a shark or other predator eat the female, the male is forced to take on the female’s role, literally. If “Finding Nemo” was based on a true story, “Marlin would have become Marlene, and mat[ed] with a younger male mate from the adolescent population already living on the anemone,” according to a university press release.

“So when Nemo finally gets back to his anemone at the end of the film, he’s actually meeting his Mum,” adds Mills, who says the research team is now investigating whether the transition stems from climate change or something else, such as boat engine noise.

The authors presented their findings at the 50th Anniversary Symposium of the Fisheries Society of the British Isles at the University of Exeter.


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