The outcome of a wide-ranging collaboration, Patek Lab members published a featured paper in the Journal of Experimental Biology about the comparative hydrodynamics of mantis shrimp strikes. This study examined the morphological and kinematic tradeoffs of fast and ultrafast motion through water over the evolutionary history of mantis shrimp. We also tested multiple approaches to the tricky challenges of fluid dynamic modeling of rotational motion through a comparison of blade-element models and computational fluid dynamic models.
McHenry, M. J., P. S. L. Anderson, S. Van Wassenbergh, D. G. Matthews, A. Summers and S. N. Patek. 2016. The comparative hydrodynamics of rapid rotation by predatory appendages. Journal of Experimental Biology 219(21): 3399-3411. Link to paper.
Abstract: Countless aquatic animals rotate appendages through the water, yet fluid forces are typically modeled with translational motion. To elucidate the hydrodynamics of rotation, we analyzed the raptorial appendages of mantis shrimp (Stomatopoda) using a combination of flume experiments, mathematical modeling, and phylogenetic comparative analyses. We found that computationally-efficient blade-element models offered an accurate first-order approximation of drag, when compared with a more elaborate computational fluid-dynamic model. Taking advantage of this efficiency, we compared the hydrodynamics of the raptorial appendage in different species, including a newly-measured spearing species, Coronis scolopendra. The ultrafast appendages of a smasher species (Odontodactylus scyllarus) were an order-of-magnitude smaller, yet experienced similar drag-induced torque as a spearing species (Lysiosquillina maculata). The dactyl, a stabbing segment that can be opened at the distal end of the appendage, generated substantial additional drag in the smasher, but not in the spearer that uses the segment to capture evasive prey. Phylogenetic comparative analyses revealed that larger mantis shrimp species strike more slowly, regardless of whether they smash or spear their prey. In sum, drag was minimally affected by shape, whereas size, speed and dactyl orientation dominated and differentiated the hydrodynamic forces across species and sizes. This study demonstrates the utility of simple mathematical modeling for comparative analyses and illustrates the multi-faceted consequences of drag during the evolutionary diversification of rotating appendages.