The largest animal on earth is a blue whale. The smallest organism (or component of life) is a virus. At both extremes, design is on display.
Blue Whale Diving Design
The heart of a blue whale, largest animal on earth, weighs as much as a cow (about 1,000 pounds, says NOAA), and pumps 60 gallons per beat. How does one measure the heartbeat of a blue whale? Ask the marine biologists at Stanford, who were so glad their method worked, they ran victory laps around their lab. First, they had to find the elusive blue whale. Then, they had to attach suction cups to the underside, equipped with electronic sensors to record the heart rate during the whale’s deep dives. Finally, they had to find the suction cups after the experiment. A floating package with GPS transmitter led them to the spot for retrieving the data loggers. When they got their data, no wonder they were excited.
The team had tried their method on smaller, captive whales before attempting the grand prize on a blue whale in the wild. According to their paper in PNAS, “Extreme bradycardia and tachycardia in the world’s largest animal,” the blue whale is at the extremes of what is possible for a heart. The heart rate, normally 25 to 37 beats per minute at the surface, slowed down to only 2 beats per minute in the deepest part of the dive. That’s much slower than they expected.
We present a major advancement in our ability to bring the physiological laboratory to the open ocean through the noninvasive use of a suction cup-attached tag equipped with surface electrodes. Our study provides heart rate data of a large, free-diving whale (blue whale) without prior capture or restraint. We recorded a wide range of heart rates from the tag, reaching only several beats per minute during deep foraging dives (bradycardia) and nearly 40 beats per minute at the sea surface (tachycardia) as the whale recovered from its oxygen debt. The latter likely represents maximal heart rate given the measured duration of the heart beat itself, thereby demonstrating the greatest dynamic range in cardiac activity at this scale. [Emphasis added.]
The results, they say, “may explain why blue whales have never evolved to be bigger.” But it would be hard to imagine any human engineer building a pump that can reproduce itself in the water, let alone achieve such high performance.
Despite high energetic demands from a large body, low mass-specific metabolic rates are likely powered by low heart rates. Diving bradycardia should slow blood oxygen depletion and enhance dive time available for foraging at depth. However, blue whales exhibit a high-cost feeding mechanism, lunge feeding, whereby large volumes of prey-laden water are intermittently engulfed and filtered during dives. This paradox of such a large, slowly beating heart and the high cost of lunge feeding represents a unique test of our understanding of cardiac function, hemodynamics, and physiological limits to body size.
From biggest to smallest: a virus, though not a free-living organism, also possesses exceptional design machinery. The T4 bacteriophage has been studied for years. It looks for all the world like a lunar lander. It lands on legs and injects DNA into E. coli. The DNA makes copies of the phage and then kills the host. Another paper in PNAS explores “How the phage T4 injection machinery works including energetics, forces, and dynamic pathway.” If measuring a whale’s heartbeat is challenging, consider trying to study a machine just 90 x 200 nanometers in size. The team of Ameneh Maghsoodi et al. found a way to do it, and started thinking about how engineers might borrow the nanotechnology they witnessed.
The virus bacteriophage T4 infects the bacterium Escherichia coli using an intriguing nanoscale injection machinery that employs a contractile tail. The injection machinery is responsible for recognizing and puncturing the bacterial host and transferring the viral genome into the host during infection. Fundamental questions remain concerning how this injection process unfolds in real time, a process that presently defies direct experimental observation. Using a combination of atomistic and continuum representations, this study contributes a system-level model of the entire bacteriophage T4 interacting with a host cell, and in doing so, it exposes the energetics, forces, and dynamical pathway associated with the injection process. The results have further implications for future nanotechnology devices for DNA transfection and experimental phage therapies.
Figure 1 from the paper shows how a sheath below the capsid, where the DNA is housed, contracts to inject the DNA into the host. First, though, protein fibers (the “legs” of the lander) attach to the host membrane. Long fibers “land” to orient the machinery. Then, a baseplate under the sheath changes shape. Short fibers extend from the baseplate and penetrate the membrane, then rotate 90 degrees to anchor them into position. The sheath goes into action!
Made up of six interacting protein strands arranged as a spiral, the sheath twists and contracts, bringing the capsid, shaped like a geodesic dome, close to the host. The capsid and sheath rotate nearly a full circle in the operation. This allows the needle-like tip to penetrate the membrane with its hard peptidoglycan shell, and insert the viral DNA into the cytoplasm.
Each component of this “injection machinery” is more complicated than summarized here, but the rotation action is shown beautifully in a short color animation of the machine in action. This is an energetic process. It takes mechanical work to rotate the device and penetrate the host. The authors measured the forces and energy costs of the machine.
Functional action like this does not just happen by chance. Multiple parts of the machinery have to work together. The authors speak of “intricate machinery” in the paper, using the word machinery 42 times, but avoiding the word evolution entirely. “Studying the structure, function, and dynamics of these nanoinjection machineries,” the scientists conclude, “has important implications for future bionanotechnologies.”
For design in the midrange, consider a new finding about honeybees. Caltech scientists found that when a honeybee is trapped in water, it can “surf” its way out, using a hydrofoil technique to give it time to escape:
Water, being a thousand times heavier than air, can prevent a bee from flying because it sticks to the wings and creates drag. The bee knows what to do. It moves its wings in a different way, something like a crawl stroke. This generates waves behind it that interfere, creating an asymmetry that moves the bee forward. Although this costs a lot more energy than flying, it gives the bee about 10 minutes to find shore and crawl out.
Slow-motion video revealed the source of the potentially life-saving asymmetry: rather than just flapping up and down in the water, the bee’s wings pronate, or curve downward, when pushing down the water and supinate (curve upward) when pulling back up, out of the water. The pulling motion provides thrust, while the pushing motion is a recovery stroke.
In addition, the wingbeats in water are slower, with a stroke amplitude — the measure of how far their wings travel when they flap — of less than 10 degrees, as opposed to 90–120 degrees when they are flying through the air. Throughout the entire process, the dorsal (or top) side of the wing remains dry while the underside clings to the water. The water that remains attached to the underside of the wing gives the bees the extra force they use to propel themselves forward.
Bees need water in the hive. They have special chambers in the mouth for catching it, but sometimes they can get stuck and drown. “The motion has never been documented in other insects, and may represent a unique adaptation by bees,” one of the scientists said, and that gave them ideas:
Roh and Gharib, who work in Caltech’s Center for Autonomous Systems and Technologies (CAST), have already started applying their findings to their robotics research, developing a small robot that uses a similar motion to navigate the surface of water. Though labor-intensive, the motion could one day be used to generate robots capable of both flying and swimming.
Design — All the Way
Whales, bees, and viruses: It’s design all the way down and all the way up. These examples each show that design science not only increases understanding of “intricate” designs in nature, it also inspires human designers to follow their lead.
Photo: A blue whale, by NOAA [Public domain], via Wikimedia Commons.