Dr Flammang then asked the question, why study fish? Fish are diverse, with many morphologies, including a variety of different fin types. There are fins adapted for swimming, fins adapted for walking, and fins adapted for adhesion. Dr Flammang's particular interest in fins was born out of boredom- while sitting in a lab dissecting a spiny dogfish (Squalus acanthias), she decided to investigate more than the usual face muscles and flanks of the little shark, and cut into the tail. In the tail, she found a bright red muscle which was not described in the literature. She dubbed this muscle the radialis muscle, and it is found in all shark species and in the torpedo rays. Certain sharks use their tails for different purposes besides swimming- thresher sharks use their extended upper fin to stun prey with a cavitation effect. Fast sharks, slow sharks- all have a radialis muscle.
To study the radialis muscle, Dr Flammang needed to make sharks swim, using a pool with a flowing current, much like a 'treadmill for sharks' with variable speed settings. Dr Flammang showed a video of a swimming shark, noting that there is little movement, small amplitude, near the shark's head and high amplitude near the tail, which moves a lot. As the sharks swam, the action of their muscles was measured using electromyography, and live recordings of muscle activity were obtained. Older models of shark fluid dynamics were two-dimensional, but Dr Flammang created a three-dimensional model to obtain a more complete understanding of what was occurring. Dr Flammang joked that previous researchers' lasers weren't as cool as hers- pulses of light from the lasers illuminated particles in the water and the movement of the particles was recorded. The typical bony fish creates a donut-shaped vortex, a ring of rotating fluid around the 'jet' of water, with its tail action (vortices like these are also produced by a duck's feet, or a piece of plastic used as a paddle). A shark, using its centralis muscle to regulate the stiffness of its tail, produces a double-vortex. Bu changing the stiffness of its tail, a shark produces thrust very efficiently- Dr Flammang joked that it is important to be stiff, and its important to be flexible.
Dr Flammang then went on to describe the bony fishes, using the bluegill (Lepomis macrochirus) as a good example- bluegill are prime test subjects, being easily kept in a lab, and being the subject of a large existing body of literature. In a typical ray-finned bony fish, there are a few spiny supporting elements giving structure to a thin membrane. There are no muscles in the fin itself, but the movement of muscles at the base of fins can alter the fin shape. The rays are flexible bones, segmented at the distal end, more rigid at the proximal end. If a fish's fins were too flexible, they would be unable to push water.
Fish live in complex habitats, and many bony fish evolved to inhabit small spaces. The rapid speciation of the bony fishes coincided with rise of corals- when corals became common, new niches opened up for the bony fish, which evolved new ways to move, find food, escape from predators, and protect their young. The Permian/Triassic mass extinction ended up being very good for ray-finned fishes.
In order to test the maneuverability of a bluegill, Dr Flammang set up an obstacle course for the fish. To impede vision, obstacle trials can be held in low light conditions. To interfere with the fish's ability to sense fluid perturbations, the fish's lateral line can be numbed. Under conditions of sensory deprivation, the fish will touch the obstacles with its fins as it navigates the course:
Fins are sensors as well as propulsion devices.
Dr Flammang then brought up a hypothetical request from the Navy in which someone, hypothetically, wished to have a device which could, hypothetically, navigate a harbor filled with obstacles, what would this hypothetical device be based on. Dr Flammang then discussed a couple of robot-fish models-a speedy 'robo-tuna' which could deliver payloads on a straightaway course, or an ocean glider which would be effective in picking up underwater samples. For harbor navigation, though, the bluegill would be the best model on which to base this hypothetical robot. Such a robot would have flexible pectoral fins and transducers to mimic the lateral line. Hovering in the water is a hard effect to achieve, thou, so more information is needed.
Dr Flammang then talked about the use of fins for walking, using the recently discovered Cryptotora thamicola, a blind cave fish which can climb up waterfalls. Dr Flammang was introduced to this fish by her colleague Daphne Soares, who was studying the loss of visual senses in cave-dwelling organisms. Dr Flammang joked that the fish had a strange way of swimming- walking on its fins with its back out of the water:
While mudskippers use their pectoral fins as crutches on land, the blind climbing cave fish moves like a tetrapod:
When the fish swims, it undulates in a typical wave-form, but when it climbs, it exhibits the lateral-sequence, diagonal-couplet gait (PDF) used by salamanders, lizards, or dogs. The fishes are too rare to be taken from the caves they inhabit, so they were scanned in the cave using equipment from a local dental school. A typical bony fish pelvis is a rudimentary basipterygium which supports the pelvic fins- the pelvic fins don't exert much force, acting as a keel, so there is no need for a rigid connection to the vertebral column. The vertebra of a typical marine bony fish doesn't have to support the fish's weight, so the individual bones don't interlock. In a salamander, the hip bones, the ilium, ischium, and pubis are fused to the vertebral column, which is interconnected by zygapophyses in order to allow it to bear the animal's weight without buckling. In Cryptotora thamicola, a flare of bone mimics the ilium. It is not known where these bones originated, whether the process was pelvis-to-spine or spine-to-pelvis. Fish do possess Hox genes which can provide a genetic underpinning for limb development.
The tetrapods evolved from fishes during the Devonian period, with lobe-finned fish like Eusthenopteron giving rise to such basal tetrapods as Tiktaalik and Acanthostega:
Dr Flammang stressed the need for more fossils of basal tetrapods in order to analyze their pelvises... we need more fossils of things that could walk on land. Physics don't change, but there are multiple strategies to move on land. We have understanding of the mechanical needs for locomotion, we just need more specimens- basal tetrapod trackways are a good source of information.
The last subject of Dr Flammang's lecture concerned fins used for adhesion- specifically the specialized fins of remoras. There are eight species of remoras, some of which have specific hosts. Remoras, which attach themselves to other denizens of the sea, gain great monbility advantages- they can attach themselves to white marlins, which can attain a speed of 40mph. Dr Flammang noted that nobody had looked at the remora's adhesive disc, which has a fabled strength. Pliny attributed Mark Antony's defeat at the battle of Actium to a remora interfering with the movement of his vessel. Remora's have been used to catch sea turtles- a line is attached to the remora, and the turtle is pulled up with the fish attached. It was largely believed that the remora's adhesive disk was a glorified suction cup. Suction cups are often used to attach sensors to whales in order to study their behavior. The remora, with its ability to adhere to a host despite changes of pressure, velocity, drag, and temperature, would be a good model for marine adhesives. Remora's closest relatives are cobias, which look like remoras without 'hats'. The remora disk evolved from the dorsal fin spines of a cobia-like ancestor. The spines migrated forward onto the head and spread into plates with spinules. The adhesive requirements of remoras are stringent- a remora attached to a blue whale travels at 50km/hr, about three-hundred times the remora's own speed, yet the remoras don't slide down the whale's body. The whales can dive hundreds of meters with seconds, exposing the remora to vast temperature and pressure changes.
NOTE... I will finish this post tomorrow... gotta go drink beer now, again.
CONTINUATION: Dr Flammang then went on to discuss the functional morphology of the remora disc- there is a fleshy lip around the lamellar array, and the spinules are of different lengths... Dr Flammang likened them to 'a bad comb'. Each lamella has individual muscular control, and the lamellae can move in order to engage the toothy spinules in order to create negative pressure and enough friction to overcome drag. The friction creating mechanism acts in a ratcheting fashion to lock the remora in place. In order to minimize drag, remoras will seek an optimal placement on a host. In order to prevent detachment through fluid seep caused by pressure differentials, the fleshy lip around the remora disc has viscoelastic properties, and mucus to help create a seal. Dr Flammang advised us that the performance of suction cups can be improved by applying mayonnaise or KY jelly to the suction cup to improve the seal.
When Dr Flammang dissected a remora, she found a series of blood vessels, a 'balloon of blood' under the disc. Remoras evolved to have anterior cardinal veins on top of their heads rather than inside their crania. By standing up, the lamellae press down on the anterior cardinal vein in order to create passive hydraulic control to prevent seep and improve suction.
Dr Flammang noted that no artificial products can minic remora adhesion... yet. Being able to mimic remora adhesion would improve the attachment of sensors to subjects' bodies- glue or sutures can cause tissue necrosis. There are medical applications- people have different degrees of hairness and moistness, so an EKG electrode able to adhere like a remora disc would be an improvement over current models.
After the lecture, Dr Flammang conducted a question-and-answer session. The first question involved marine mammals swimming abilities, and Dr Flammang noted that cetaceans are secondarily aquatic, so their tetrapod morphology is imposed on their swimming style- it's easier for mammals to flex their spines back and forth rather than side-to-side. A wag asked Dr Flammang if punching a shark in the nose will stun it, and Dr Flammang noted that it is difficult to punch things underwater, so she doesn't sugggest it... she did offer the advice that sharks are attracted to the scent of urine, so try not to pee in the sea. Regarding a question about fish in space, Dr Flammang noted that their locomotion hasn't been studied in any detail, but she totally wants to try it. Some Bastard in the audience asked her if the locomotion of flatfish has been studied, and she noted that one of her colleagues has begun to study them, and one avenue of inquiry involves the fishes' ability to stiffen their skins- the most important locomotor activities that flatfish have adapted to excel at seem to be attaining lift, and burrowing.
Once again, the Secret Science Club delivered an amazing lecture- kudos to Dr Flammang, Margaret and Dorian, and the staff of the beautiful Bell House. I have often said that I am most interested in biological topics, so this lecture was particularly suited to me. Dr Flammang knocked it out of the park, hitting that 'Secret Science Sweet Spot' with her combination of humor (I'm still chuckling about her discovery of the centralis muscle), description of methodology, richness of information, and great video footage. Here's a hearty high five to the good doctor.
After the lecture, Dr Flammang hung out with us for a while, but was unable to join us in a drink because she's expecting twins in November- another high five! Talking about designing robots, she mentioned that she knows Dr John Long of Vassar who lectured on the evolving swimming robot... there's an effect I call 'Secret Science Synergy', the cumulative effect of attending multiple lectures improves each lecture.
Here's a video of Dr Flammang discussing modeling robots on marine animals:
Pour yourself a libation, and soak in that SCIENCE!
2 comments:
Great stuff. Just superb. Thanks so much.
It's really a pleasure and a privilege... it's also a duty to Margaret and Dorian, and the scientists who lecture. Thanks for reading.
These are the most important blog entries I write, and the composition of them forces me to bring my writing 'A' game. There's no goofing off here like there is in snarking or posting cat pictures.
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