The Pacific snake cod is a malfunerous omnivorous fish with a mouth like a messy silver drawer, its more than 500 teeth arranged haphazardly on two sets of highly moved jaws. New research published this month in the scientific journal Proceedings of the Royal Society b shows that the Pacific cod grows and loses an average of 20 teeth per day.
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If this is the case with human teeth, it is equivalent to us changing one tooth every day. Adam Summers, a professor of biology at the University of Washington and co-author of the study, said: "This makes braces useless. And brushing your teeth. ”
Karly Cohen, another co-author of the study and a phD student at the University of Washington who studies the biomechanics of feeding, said the rate of tooth replacement in the Pacific snake cod surprised the researchers.
"Our existing research on tooth replacement comes from strange things like a squid or piranha that grows teeth on its forehead, and it can lose a quarter of its teeth at a time. But most fish have teeth like snake cod. She added that it is therefore likely that most fish lose a large number of teeth every day and replace them quickly.
An ambush predator with teeth
The Pacific snake cod is a grumpy sporting fish that grows about 4 feet in length as an adult and is an ambush predator who often indulges in cannibalism. Spread across the west coast of North America, from Alaska to Baja California, Mexico, it is of great economic importance to fishermen, in part because it is suitable for making tacos.
But they are not a fascinating fish. Emily Carr, an undergraduate at the University of South Florida and lead author of the study, said: "I always joke that the snake cod and I have never been together. We had to add tape to the corners of the tank because when they saw someone walking by, they would try to jump out... I've never been bitten, but I'm sure they'll try if given the chance. ”
Cohen notes that as a greedy hunter, the snake bass will eat anything that can be stuffed into its mouth.
"Snake cod have a set of upper jaws and lower jaws, just like ours, but they're more flexible — they can be thrown forward and unfolded. If you look at the inside of their mouths on their palates, there are also teeth covered. "Then, all the way to the back of the throat, just before their esophagus, where there is the pharynx, a bony platform with teeth made up of modified gill arches."
When the snake cod attacks, its first set of jaws is fired forward and dragged into the prey into its mouth, and the jaws on the inside of the pharynx begin to work and are crushed and shredded. To make this strategy a success, the cod relies on needle-like sharp teeth that can easily break. But how to keep its bite force from becoming blunt? The strategy seems to be - to keep growing new teeth, a lot of teeth.
The fate of teeth
In this study, the researchers used a range of dyes to create a visual timeline of tooth growth.
First, 20 juvenile snake cod are soaked in a tank with the fluorescent dye alizarin red added for 12 h. Since alizarin is attracted to the calcium in the teeth, hundreds of glowing red teeth are revealed as a result. Over the next 10 days, batches of cod were exposed to a second green dye, fluorescein. On the first day of the study, the teeth were dyed red, while the teeth that later erupted appeared green.
Carr painstakingly counted and sorted each Of the Christmas-colored teeth, and it is reported that a total of 10,580 teeth were found in the 20 fish examined.
After examining the smiles of each of the 20 fish, Carr and her team learned that the snake cod's teeth were predestined, meaning that each tooth would erupt accurately over the course of its destined career. This is in contrast to other well-known dental fish such as the great white shark, whose teeth start small at the back of the jaw but move forward as they grow.
The researchers also identified hotspot locations for tooth replacement. Cohen said: "It's not that the real big teeth stay there longer, or that the real little teeth are constantly being replaced. We found that in places where we expected more power, teeth were replaced faster. ”
But what triggered the tooth replacement of the snake cod? The second experimental condition in the study compared fish that were fed regularly with another group of fish that were not fed. The researchers found no significant difference in tooth replacement rates between them. This suggests that the cod doesn't only grow teeth when it breaks — it may be more like our own deciduous and adult teeth, and their shedding and germination are based on a genetic timer.
Carr said she found the replacement rate of snake cod to be surprising. "There is an idea that while the manufacture and replacement of teeth is very expensive, our research challenges this concept." In the calcium-rich ocean waters, keeping them sharp with their teeth is clearly a worthwhile investment for snake cod.
Heterogeneous and snake cod
This pattern of tooth growth is an unusual pattern in the field of fish research, but may not be in nature. The teeth of the cod are very similar to those of other bony fish, in number, variety, and in their cone shape. Marc andré Meyers, a professor in the Department of Materials Science and Engineering at the University of California, San Diego, said this makes it a great model for many different species from different pedigrees, and sequential staining of teeth quantifies this in a beautiful way.
Willy Bemis is a professor of ecology and evolutionary biology at Cornell University, specializing in the anatomy of fish — including the development of teeth. He wasn't involved in the study, but he thinks the experiment was designed to be innovative and would help answer long-standing questions about tooth replacement in relatively normal fish like snake cod.
Historically, bemis says, the rate at which fish teeth grow and fall out has been difficult to estimate — for example, for sharks, the best data comes from studies that collect and calculate the loss of teeth found at the bottom of tanks. Since sharks have been observed feeding on their own fallen teeth (perhaps to recoup their calcium investments), the data is always a little dubious.
Bemis said that because the study of the snake cod demonstrated a technique that can be replicated in other species, it makes it an important piece of work. Meyers said he is interested in conducting similar studies on piranhas.
These results suggest that teeth may not be as irreplaceable or precious as we think.