FYFD

Tag: biology

  • Water Anoles Breathe Underwater

    Water Anoles Breathe Underwater

    Meet the water anole, a small lizard native to the tropics of Central America. While studying these anoles, researchers discovered that they could flee underwater and remain submerged for 16 minutes or more at a time. Curious to see how the lizard manages this feat, they filmed them underwater, discovering that the anole seems to exhale a small bubble that sticks on its face and then re-inhale it.

    How exactly this built-in “scuba gear” works is still under investigation, but here’s my guess. Fresh oxygen can diffuse from water into a bubble; some insects use this to breathe underwater. The natural, random motion of molecules tends to cause chemicals to move from areas of high concentration to those of low concentration. But this molecular diffusion is extremely slow. That tiny bubble you see isn’t around long enough for any significant molecular diffusion of fresh oxygen. But what if the surface of the bubble is actually much larger?

    Notice the silvery shininess we see on the anole. That’s because most of the lizard isn’t actually wet. The anole is superhydrophobic, so its skin has trapped a thin layer of air that appears to extend over a large part of its body. I think perhaps the anole has fresh oxygen diffusing into the air layer across most of its skin, and the large bubble it inhales and exhales serves as a sort of pump to help draw that fresh oxygen through the air layer and into its body. That could help explain how the anole can stay submerged for so long.

    As researchers continue to investigate this little aquanaut, it will be interesting to discover just what its secrets are! (Image and video credit: L. Swierk; via Gizmodo)

  • Finding New Shapes in Foam

    Finding New Shapes in Foam

    In the summer of 2018, a group of researchers announced they’d discovered a new geometrical shape, the scutoid. They found the scutoid, a sort of twisted prism, in the shape of epithelial cells packed between curved surfaces. Having heard of this new geometry, a different group of physicists wondered if they could find scutoids elsewhere, specifically, in the cells of a foam. As shown in the picture above, they did.

    To visualize a scutoid, first image a prism. Take two polygons with an equal number of sides and connect them. But if you imagine packing such prisms between two curved surfaces, you’ll quickly see that it won’t work. They just don’t fit together. Instead, one face may adopt, say, six sides, while the other takes on five. To join those two end faces, one of the sides will have to have a Y-shaped junction and a triangular face. This is a scutoid.

    You can see two such shapes in the image above. In the left bubble, the far side forms a pentagon, while the near face is a hexagon. On the right, the bubble has six faces in the background and eight in the foreground. And between them, you can just see the triangular face that connects the two scutoids.

    It’s not only exciting to find scutoids in a new, non-biological medium; it suggests a physical mechanism behind their formation. Foams are a well-known example of energy minimization. The fact that scutoids are found in a curved foam suggests that the shape itself is connected to energy minimization, something that could help us understand how biological scutoids grow and form. (Image and research credit: A. Mughal et al.; via Physics World; submitted by Kam-Yung Soh)

  • Sniffing Underwater

    Sniffing Underwater

    Star-nosed moles – tiny mammals native to the northeastern United States – have an underwater superpower: sniffing. To seek prey underwater, the moles blow bubbles and suck them back into their nostrils in about a tenth of a second. Their eponymous noses seem to be key to this, as seen in newly published research. Researchers built model star noses from plastic (lower right) to explore how well different shapes could hold the bubble in place, a necessary ingredient for the mole to sniff them back up. 

    With a perfectly flat plate, any small tilt makes the bubble slide toward the edge and float away. Star-shaped ones, on the other hand, can hold a bubble even up to a 7-degree tilt angle, a 40% improvement. The spacing of the gaps is also important. If they’re too wide, buoyancy can pull the bubble up through them. But if they’re too narrow for the bubble to deform upward through them, they make poor anchors. 

    Understanding the mechanics of underwater sniffing is good for more than just appreciating this funny-looking mammal, though. The researchers hope their findings will help develop underwater chemical sensors that use bubble sniffing instead of exposing their components directly to sea water, which would significantly extend their usable life. For more, check out the paper and my interview with the lead author in the video below. (Image credits: top and lower left – K. Catania; lower right – A. Lee; research credit: A. Lee and D. Hu; video credit: N. Sharp and T. Crawford)

  • Inside a Heart

    Inside a Heart

    You may not give it much thought, but there is important fluid dynamics happening inside you every moment of every day, especially inside your heart. Of the four chambers of the heart, the left ventricle has the thickest walls, reflecting its important task: pumping oxygenated blood throughout the body. In a healthy heart (top of poster; click here for the full-size version), a vortex ring and trailing jet fill the ventricle when the mitral valve opens. Then the ventricle contracts and pumps blood out the aortic valve and into the rest of the body.

    But for individuals with a leaking aortic valve (bottom of poster), things look different. Blood leaks back through the aortic valve at the same time that the mitral valve opens to allow freshly oxygenated blood back in. The two inflows disrupt mixing in the chamber, and, instead of pumping fully-oxygenated blood into the body, the left ventricle has to struggle to pump a less-oxygenated mixture into the body. (Image credit: G. Di Labbio et al.)

    ETA: (Research paper: G. Di Labbio et al., arXiv)

  • Fighting a Viscous World

    Fighting a Viscous World

    Vaucheria is a genus of yellow-green algae (think pond scum), and some species within this genus reproduce asexually by releasing zoospores. Once mature, the zoospore has to squeeze out of a narrow, hollow filament in order to escape into the surrounding fluid (top). To do so, it uses tiny hair-like flagella on its surface. Despite the minuscule size of these micron-length flagella, they generate some major flows around the zoospore (middle and bottom). Even several body lengths away, the flow field shows significant vorticity. All this active entrainment of fluid from the surroundings helps the zoospore escape its confinement and swim away to start a new plant. (Image and research credit: J. Urzay et al., source)

  • Review: “How to Walk on Water and Climb Up Walls”

    Review: “How to Walk on Water and Climb Up Walls”

    “An eight-year-old girl kicked her feet back and forth on the seat of a Long Island Railroad train. I beckoned her to cover over and pointed to the top of my winter jacket, which I slowly unzipped. Inside, nestling against me for warmth, were ten snakes, their forked tongues waving back and forth. The child shrieked and ran back over to her mother, who was napping. ‘That man has a coat full of snakes,’ she shouted.”

    So begins Chapter 2 of Dr. David Hu’s new book, How to Walk on Water and Climb Up Walls (*), a captivating and funny journey through animal locomotion and biorobotics. Don’t let that fool you, though; this book has plenty of fluid dynamics to it. Long-time FYFD readers will recognize some of the topics, such as the fluid-like behavior of fire ants, how eyelashes keep our eyes clean and moist, and why swimming behind an obstacle is so easy even a dead fish (like the one shown above) can do it.

    There are plenty of exciting, new stories as well, like how sandfish – a type of lizard – can swim under sand and why a lamprey’s nervous system may lead to better robots. The explanation of how cockroaches are virtually unsquishable and able to squeeze themselves into crevices a quarter of their height absolutely floored me. 

    Hu’s book offers a front-row seat to research at the cutting edge of biology, engineering, and physics, with anecdotes, explanations, and applications that will stick with you long after you put the book down. If you’re looking for a holiday gift for yourself or another science-lover, check this one out for certain (*).

    *Disclosures: I purchased my copy of this book using my own funds, and this review is not sponsored in any way. This post contains affiliate links – marked with (*); if you click on one of these links and purchase something, FYFD may receive a small commission at no additional cost to you.

    (Image credits: book – Princeton University Press; fish – D. Beal et al.; ants – Vox/Georgia Tech; eyelashes –  G. Diaz Fornaro; shark denticles – J. Oeffner and G. Lauder)

  • Water-Walking Geckos

    Water-Walking Geckos

    Many animals can run on water. The tiniest creatures, like water striders, use surface tension to keep themselves atop the water.  Larger creatures like the basilisk lizard or the grebe slap the water’s surface to generate a vertical impulse that keeps them aloft. Geckos, it turns out, can run on water, too, but they’re too big to stay up with surface tension and too small to support their weight by slapping. So they’ve developed their own method.

    As you see in the top image, geckos use the slapping method for part of their support. Their slaps generate a little less than half of the force needed to keep them out of the water. 

    Surface tension is an important component, too. Geckos are extremely water repellent, which helps boost the lift they get from surface tension. In the bottom image, you see a gecko attempting to run on soapy water, which has a lower surface tension. The gecko is mostly submerged and more swimming than running – a clear demonstration that surface tension is important to its water-walking.

    Finally, the gecko undulates its body as it runs, much the way an alligator swims. The researchers suspect this helps the gecko generate forward thrust. Altogether, it creates a water-walking gait that, for now, is unique among observed mechanisms. (Image and research credit: J. Nirody et al.; via Ars Technica; submitted by Kam-Yung Soh)

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    Underwater Snakes, Gusty Flying, and Microswimmers

    If you like your fluid dynamics with a healthy dose of biology, this video’s for you! Learn about the hydrodynamics of snake strikes, how birds fly in gusty crosswinds, and the mathematical underpinnings of a microswimmer’s journey. This is the final video in our FYFD/JFM collaboration featuring research from the 2017 APS DFD meeting. If you missed any of the previous videos, you can see them all here. Which one is your favorite? Would you like to see the series continue? Let me know in the comments or on Twitter! (Image and video credit: N. Sharp and T. Crawford)

  • Rattling Feathers for Attention

    Rattling Feathers for Attention

    Peacocks are known for their colorful mating displays, but it turns out there’s more to them than meets the eye. To help them gain a penhen’s attention, peacocks will sometimes rattle their train-feathers. The sound this makes is mostly below the range of human hearing, but the rustle creates subtle vortices in the air that cause the feathers atop a peahen’s head to vibrate. Playing back the sound at peahens from typical train-rattling distances also gets the females’ attention. Researchers found the playback makes peahens’ crests vibrate at a resonant frequency, suggesting that these feathers are for more than display; they’re used for communication as well! (Image and research credit: S. A. Kane et al.; video credit: Science)

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    The Clever Cat’s Tongue

    Cats spend almost a quarter of their waking hours grooming, and their tongues are wonderfully specialized for this task, allowing them to clean, cool, and untangle themselves with ease. Anyone who’s ever been licked by a cat knows their tongues feel sandpaper-y. This is due to rear-facing hook-like structures called papillae that have a stiffness comparable to human fingernails.

    The papillae are hollow, and their U-shaped tip helps them wick up saliva, which the cat deposits deep into its undercoat when it licks. Although the papillae only hold about 5% of the volume of saliva on the cat’s tongue, this wicking action is key because most of the tongue surface can’t reach the inner coat; only the papillae do. The saliva that reaches these dense inner hairs is important not only for cleaning the fur, but for helping the cat cool off. As the saliva evaporates, it carries heat away with it, just like sweating does for us.

    The papillae are key to untangling fur, but their shape also makes it easy to remove hairs caught on the tongue. Researchers built a 3D-printed cat-inspired hair brush to show how efficient and easy to clean a cat’s tongue can be! (Video credit: Science; research credit: A. Noel and D. Hu)