Muscle tradeoffs in a power-amplified prey capture system

Should animals operating at great speeds and accelerations use fast or slow muscles? The answer hinges on a fundamental tradeoff: muscles can be maximally fast or forceful, but not both. Direct lever systems offer a straightforward manifestation of this tradeoff, yet the fastest organisms use power amplification, not direct lever action. Power-amplified systems typically use slow, forceful muscles to pre-load springs which then rapidly release elastic potential energy to generate high speeds and accelerations. However, a fast response to a stimulus may necessitate fast spring-loading. Across 22 mantis shrimp species (Stomatopoda), this study examined how muscle anatomy correlates with spring mechanics and appendage type. We found that muscle force is maximized through physiological cross-sectional area, but not through sarcomere length. Sit-and-wait predators had the shortest sarcomere lengths (fastest contractions) and the slowest strike speeds. The species that crush shells (“smashers...