Under the waves, tiny clams with shells usually about the size of a pea bore into sunken wood. The wood is a source of sustenance for them. There are pieces of wood sunken in the water where different wood-boring clam species can live in harmony for a long time. One group of wood-boring clams has evolved a unique way to get the wood all for themselves: building chimneys made of poop.
Getting pure water in, so you can get oxygen to your gills, and getting rid of your waste are two challenges every sea creature faces. People don't want to live in their feces. Janet Voight is the Associate Curator of invertebrate zoology at the Field Museum and the study's lead author.
Voight says that scientists can put wood on the ocean, return months or even years later, and recover it with an amazing array of animals. Voight wanted to know why this was different.
She noticed a pattern when she looked at the clam species present in reports of sunken wood. Voight says there are six main branches in the wood-boring clam family tree, and every woodfall that was bored so heavily it was crushable by hand turned out to have been bored by a species from the same single branch.
"That's not supposed to happen, you just assume that all wood-boring clam species, which look pretty similar, bore into wood the same way," she said. One group is doing something completely different.
The very nature of the clams may be to blame for the extra-chewed-up wood. All of these species have a trait where the sun isn't shining. clams fill the space around them in the holes with their own feces as they dig in the wood
Voight said that they don't do it on purpose. The clams have little shells that do the boring. The clams have tubular appendages that they use to take in water and expel waste. Voight says that in most wood-boring clams, the two "in and out" siphons are the same length.
The suck for expelling de-oxygenated water and feces is short in these borers. Voight says that they poop in their hole. Unless they really, really push, they need to. The waste stays with the clam and forms a chimney.
Voight says it's surprising that animals would evolve a body that keeps them in contact with their own waste. They seem to be going to town on the wood. They evolved this way.
She and her colleagues thought that these fecal chimneys might be able to detect the poop and make their way to it to join their own species.
Even if a poop chimney serves as a beacon for other members of their species to join them on their wood, how can these individuals survive when the environment becomes filthy and oxygen is hard to come by?
Voight says that the group of clam has been shown to be tolerant of low oxygen in the past. The lining of their fecal chimneys and the substance in their blood that picks up oxygen may reduce the risk of poisoning from the waste.
These species are able to survive in conditions that would make non- related wood-boring clams sick. The result is more wood for the chimney- producing species to eat, live in, and for their offspring to be free from competitors.
The study shows the importance of looking at ecology with an understanding of how different species are related to each other.
Voight says that sometimes you need to step back and look at the big picture, put a lot of different studies together, to see how what had appeared to be enigmatic is a product of evolution. The more we know about the evolutionary histories of different groups, the more we can find out about how they fit together.
Competition in the deep sea is related to the impact of wood-boring xylophagaids. It's called 10.1007/s12526 022-01306-z.
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