Reuben Shipway is a scientist at the University of Postsmouth (England) who has one of those jobs that you hardly imagine as a child when you fantasize about what you want to be when you grow up. He studies the sex life of woodworms, white-bodied bivalve mollusks known in the world’s oceans for feeding on submerged wood. Ships, docks and marine defenses are in the throes of a diet that, by the way, costs billions of euros every year.
These animals, also called jokes, are not only characterized by piercing ships. They also have a sexual activity capable of impressing anyone. And Shipway’s team was the first to capture it on video. The description of the images could be the plot of an adult film: a competitive sexual frenzy in which the larger appendages are more successful. But here the comparisons end, because these little mollusks are used in the matter in a way that is difficult to imagine.
The protagonists of this exalted “orgy” are, in particular, the Bankia setacea. With their long worm appearance, they are very different from other marine mollusks such as clams or mussels. “When we first noticed that these animals were reproducing in the aquarium, we couldn’t believe what we were seeing. They were using their siphons to wrestling, inseminating each other, and swapping sperm. As far as we know, this struggle had not been observed before, “says Shipway, who has published his findings in the journal” Biology Letters. “
These fluid genus animals have two long siphons, one used to breathe water and the other to expel waste. They are the only parts that stick out of the wood. “Most of the time, they are not very interesting to look at. One day I was in the aquarium and I realized that there was a thick column of creamy liquid in the tank, which I knew had to be eggs and sperm, ”says the scientist. “When I got a little closer, I saw that the siphons of these animals were going crazy and I was witnessing a sexual frenzy, and I decided to film it,” he stresses. When he returned a few hours later, the worms were “still at it.”
Back and forth sperm
The researchers recorded several shipworms mating with each other, some receiving sperm and planting their own sperm in a different individual at the same time. Some are seen extracting sperm from themselves, and others shedding their rival’s sperm while trying to reproduce.
Inside a piece of wood, 74 of the 79 shipworms engaged in pseudo-copulation (copulation-like behaviors with a reproductive function but not involving actual sexual union between the individuals), while five remained on the sidelines, housed instead in the wood, too far to participate.
The team identified clear stages of sperm transfer from shipworms. First, the recipient’s siphon becomes inactive and opens completely. The donor siphons then crawl across the surface of the wood until they find a neighbor’s recipient siphon. Once they have found the recipient, the siphons intertwine and the donor transfers the sperm to the recipient. In areas of high competition, siphons fight for access to a partner. After the transfer of sperm, the fertilized eggs are released into the sea.
Competitive mating and pseudo-copulation are known to occur in only a handful of marine invertebrates. “It is a rare and sophisticated form of reproductive behavior, with fights between rival partners, bringing potential partners closer and away from rivals, and going so far as to get a rival’s sperm out of a siphon to float,” he describes Shipway.
Bigger the better
The researchers think that shipworms that grow rapidly to a larger size may have a competitive advantage because they have longer siphons, so they go further to fend off rivals and fertilize their neighbors.
Although these creatures get a bad press for eating wood from ships, the researchers recall that they play an important role in the ocean’s carbon cycle. New research on their bacteria suggests that they are potentially important for the discovery of new drugs in the fight against antibiotic resistance. The enzymes in its guts have high potential for use in the production of biofuels.
As Nancy Treneman, a member of the research team, recalls, “Humanity’s battle for millennia with these fragile animals to limit their voracious appetite for our wooden ships, docks and levees has met with limited success. Studying their reproduction increases our understanding of their place in the ocean’s web of life and how we might one day keep ships from being eaten. ‘