Pity the poor tubeworm, whose life is fraught with risk. Like many marine invertebrates, the worm spends its earliest days as a tiny larva drifting in the plankton — but sooner or later, it must choose a place to settle down. Once cemented to a hard surface, it begins the massive shape change called metamorphosis, from which it emerges in its splendorous adult form.
There are no second chances: A worm that picks a bad spot can’t try again. Faced with such a momentous decision — the most important of its life — the larva needs all the help it can get. Often, that help comes from another kingdom of life altogether.
Scientists have known for several decades that some animal larvae, including those of tubeworms, select sites for metamorphosis by monitoring chemical signals released by bacteria. But they’re just beginning to realize how widespread the relationship can be, and how sophisticated — sometimes involving specialized bacterial machinery to deliver signals to larvae. This implies that communication between animals and bacteria in the oceans could be much richer and more cooperative than previously suspected.
And there could be practical applications: Experts may someday find ways to manage this communication to encourage animals to settle in some places, such as oyster farms, and discourage them in others, such as the hulls of ships.
It’s hardly surprising that tubeworms and other planktonic larvae rely on bacterial cues to help select a suitable spot for metamorphosis. After all, a thin layer of mixed bacterial species — called a biofilm — coats every available ocean surface. What’s new is the emerging breadth of this phenomenon. “In every major branch of the animal tree of life, there are species that undergo metamorphosis in response to bacteria,” says Nicholas Shikuma, a microbiologist at San Diego State University who coauthored a look at how bacteria influence animal metamorphosis in the 2021 Annual Review of Microbiology.
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