The partnership between clownfish and sea anemones is one of the most iconic in the animal world. Unlike in Pixar’s film Finding Nemo, clownfish seldom stray far from their anemone. During the day, they dart through the water overhead to catch morsels of food. At night, they snuggle deeply within the stinging tentacles. And the nocturnal half of this routine is still providing us with fresh surprises.

For ages, everyone thought that the two partners were a joint self-preservation society. The anemone’s tentacles provide the clownfish with protection from predators, while the clownfish chase away butterfly fish that would eat the anemone. More recently, Nanette Chadwick from Auburn University in Alabama showed that the fish also fertilise the anemone with