HOW DOES THE LARGEMOUTH BASS DO IT?
The eponymous maw of the largemouth bass — and the fish’s ability to suck prey into that gaping gullet in a rapacious strike — are part of the lore and legend of the bass to the many anglers who pursue it. But they are not the only ones who are fascinated.
The functioning of the mouth of the largemouth is also of interest to scientists trying to understand how joints and other complicated biological structures work.
The bass’ mouth is full of bones and muscles, but the parts that function in its rapid vacuum-cleaner attack fit a model that engineers call a four-bar linkage — four rigid sections linked by flexible joints.
Aaron Olsen of the University of Chicago, with Ariel Camp and Elizabeth Brainerd of Brown University, used X-ray videos to create the most accurate representations yet of how that mouth works.
An analysis published in The Journal of Experimental Biology confirmed that the mouth is indeed a four-bar linkage — with three degrees of freedom. That’s a mouthful, but it really means that each linkage can move on three different planes.
The New York Times talked with Olsen about the research. The conversation has been condensed and edited for space and clarity.
Q: What is your research about?
A: I study the evolution of motion in vertebrates.
Q: Why largemouth bass?
A: They’re easy to get, and bass are powerful suction feeders, which was of interest to Ariel and Elizabeth. And there’s been a lot of work previously on largemouth bass.
Q: How do you get such clear reconstructions of the moving bones?
We implant little metal beads in the bones and then film the fish from two different X-ray views. With X-rays, we can see how the bones are moving. Then we CT-scan the fish and align each
A:
scanned bone with the X-ray video, using the beads as anchor points. So the reconstructed motion you see is actual live motion.
Q: You found these connections with three degrees of freedom. What’s a egree of freedom?
A: You can think of degrees of freedom as the number of different ways you can move something. For example, a hinge has one degree of freedom while a ball and-socket joint has three.
Q: Why bother to study this?
A: Fish heads are a great model for nderstanding how joints work and how ones move. And biomechanics researchers have collected motion data from many other species, including, pigs, birds nd turtles. So one of my goals over the ext few years is to link the shape of diferent joints across animals to the motion we see at those joints. Human joints in a diseased state may resemble nonhuman joints, such that exploring the diversity of joints among animals may actually be informative for human oint diseases. I don’t know if that will be he case, but I think it’s worth exploring.