The social dynamics of clownfish are not as simple as the adoring father-son relationship of Marlin and Nemo in Disneys iconic films Finding Nemo and Finding Dory. The reality for these brightly hued orange-and-white fish is far more complexand one that has long stumped evolutionary biologists. Peter Buston, a Boston University College of Arts & Sciences associate professor of biology, has been studying clownfish for over two decades, and has housed hundreds of these fish in his Marine Evolutionary Ecology lab.

One major difference between Nemo and real-life clownfish is that they dont always live with their biological relatives. Instead, groups of up to six cohabiting fish are led by a femalethe queen bee of the clownfishwhile living in friendly competition with one another based on their size and color. Only the largest of the group mates with the reigning queen.

Fascinatingly, all clownfish are born male, with the capacity to change gender later in life. Once the female of a group dies, the next largest in the group changes gender from male to female, and becomes the new leader. The smaller fish all move up one spot in the social ladder, waiting their turn until theyre next in line to mate.

The idea that the smaller, duller-colored clownfish put up with this arrangement fascinates Buston. Through his research, he has tried to figure out why this social hierarchy doesnt lead to the smaller fish leaving their home anemonewhich live attached to the seafloor or coral reefs and have long tentaclesto breed elsewhere. In a 2020 paper, Buston found that a combination of ecological and social constraints seem to be the reason for them staying. Clownfish didnt even leave when presented with a nearby alternative, because of the risks of entering a new home, and most of them returned to their original anemone after being moved to a different one.

Their behaviors can be quite complex, says Buston, who has studied clownfish behavior both in the lab and in the wild. And clownfish and anemones have a quintessential symbiotic relationship. In the ocean, sea anemones trap food with stinging cells on their tentacles that paralyze their prey. Clownfish, though, secrete a mucus that shields them from the stings. The bright-colored clownfish attract predator fish to the anemone, which then stings and eats the fish. And in return, the anemone provides a safe, protected environment for the clownfish.

To make matters more complicated, Buston and his team have found that clownfish can control their growth depending on the specific social contextso two rival males put together will race to get bigger and become dominant. The team is currently investigating the genetic mechanisms that allow the fish to do this. Theyve also learned how to introduce baby clownfish to new social groups in different-size anemones and created more than 10 social groups in the labwith aims to create more soon.

Watch the video above to see the clownfish in action.

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Clownfish: Studying their Complex Lives and Anemone Homes | The Brink - Boston University