Meeting Abstract

20.2  Monday, Jan. 4  Comparative muscle physiology of the mantis shrimp’s raptorial appendage MENDOZA BLANCO, M.A.; PATEK, S.N.*; Univ. of California, Berkeley; Univ. of Massachusetts, Amherst marco_mendoza@berkeley.edu

Some mantis shrimp (Crustacea: Stomatopoda) deliver forceful blows with hammer-like appendages (“smashers”), while other species use elongated spears to pierce or grab prey (“spearers”). To accomplish these incredibly fast movements, mantis shrimp use extensor muscles in the merus segment of their raptorial appendages to load elastic exoskeletal structures while flexor muscles engage latches to hold the system in place. Once ready to strike, the flexor muscles relax, the latches release, and the appendage rotates forward at remarkable speeds and accelerations. We examined variation in the lateral extensor muscle across stomatopods using physiological cross-sectional area (PCSA) and sarcomere length (SL). PCSA represents relative muscle force and was calculated by measuring the mean pinnation angle and apodeme area (15 species, 60 individuals). SL provides a relative measure of the rate of muscle fiber contraction, with longer sarcomeres yielding more forceful contractions and shorter sarcomeres yielding greater contraction speed. We measured muscle fibers sampled from 4 regions of the muscle (11 species and 30 individuals). PCSA and apodeme area were positively correlated with merus and body size in all species. “Smashers” had relatively larger merus lengths and associated PCSA than “spearers”; however, pinnation angle was similar (37-38°) across all measured taxa. Smasher sarcomeres were 11-13 µm long while spearer sarcomeres were 8-10µm. In conclusion, smashers have both higher PCSA per body size and greater SL than spearers. These results suggest that smasher muscle physiology is tailored toward greater force whereas spearer physiology is geared toward higher speed contractions. Thus, mantis shrimp have evolved distinct patterns of muscle anatomy and physiology which may underlie their remarkable variation in prey-capture strategies.