The CT scans and other research found high material density in two bar-like structures in an appendage from G. smithii, a mantis shrimp species known for its speedy blows. “That got me thinking,” Rosario says. “Functionally, does that play a role? If we load this model of the appendage, do we see a high density of energy where we also see a high density of mineralization?”
Rosario’s models calculated how much energy is stored in each virtual brick – or region of the appendage – under different loading conditions. In initial studies, he found that when the claw was compressed, elastic energy was highly concentrated in the mineralized bars, as he suspected. Rosario compared that against a model of an appendage from L. maculata, a mantis shrimp species that typically spears its prey while releasing its claws at a slower speed. The calculations showed energy was spread throughout the entire appendage, rather than focused in particular places.
That could mean the more diffuse energy density in L. maculata translates into a slower speed than the concentrated energy approach in G. smithii, Rosario says. But he also speculates “these different structures are viewing energy density in different ways.” Loading elastic energy into one or two areas, like the mineralized bars, puts added strain on those parts, increasing the risk of failure. Spreading the energy throughout the appendage lessens the strain on any one spot. “You end up with somewhat of a more robust structure.”
Patek’s work has gained international attention, most recently from the National Geographic WILD channel on cable television. “Ninja Shrimp,” which has been showing this spring, includes Rosario demonstrating both his claw-compressing experiment and the computer models.
Studying biological structures involved in elastic energy storage could provide ideas to build better structures for similar purposes, Rosario says. Robots designed to explore planetary surfaces, for instance, would benefit from an energy-efficient way to jump over obstacles.
The research also provides insights into the evolutionary process. In broad terms, Patek says, “what we’re hoping to understand is the interface between physics and evolution.” Many organisms have elastic energy mechanisms, and biologists generally understand how each works. Little has been done, however, to compare these systems across species. By examining how they differ “we can probe the evolutionary history of the system,” including why some parts changed and others didn’t to achieve different purposes.
Comparing elastic energy mechanism parts and variations has many computational components, Patek says, making the rigorous training Rosario receives through the DOE CSGF especially useful. Although experience in computation and mathematics isn’t uncommon among biomechanics researchers, “he has a skill set we didn’t have. That means he now can think about asking questions we didn’t think we could ask before. We can do things we didn’t think we could.”
Rosario plans to continue adapting computer codes, which will let him explore deeper mysteries of the mantis shrimp. For instance, the model now calculates energy distributions only at the beginning and end of compression and merely interpolates what happens in between. Rosario wants to base the progression on hard calculations.
The model also assumes an appendage’s composition is pretty much homogeneous throughout. Working with polymer scientists, Rosario hopes to characterize an appendage’s material properties at the nanoscale and address questions connecting them to time scales. “It takes about 2 seconds for these appendages to load, but they strike within milliseconds, so there’s definitely something going on at the polymer level. I’d like to test some of my theories out with these computational models.”
Greater understanding of modeling has opened new horizons, Rosario says. “Without the mathematics and the computation, I would be blind in terms of where this energy is being stored. This computation has given me the ability to look at things that weren’t possible” to see.
Thomas R. O'Donnell is senior science writer at the Krell Institute and a frequent contributor to DEIXIS.