Meeting Abstract

P3.134  Thursday, Jan. 6  Effects of relative body wall thickness on the magnitude of gradients of strain in the Long-finned Squid, Doryteuthis pealeii TAYLOR, Kari R.*; THOMPSON, Joseph T.; GENTILE, Christopher; Franklin and Marshall College; Franklin and Marshall College; Franklin and Marshall College kairit03@gmail.com

The current paradigm of striated muscle function assumes that all muscle fibers within a single muscle shorten the same amount and produce the same force during a given behavior. However, a model of hollow, cylindrical muscular organs, such as the mantle of squid, predicts large and non-uniform length changes (i.e., strain) in the circumferential fibers of these organs. We previously confirmed the presence of non-uniform shortening, which resulted in a gradient of strain and strain rate, in the mantle of adult Doryteuthis pealeii (i.e., the fibers near the inner surface of the mantle experience greater strain than those near the outer surface for a given mantle contraction). The model also predicts that the magnitude of the gradient of strain and strain rate increases with increasing relative mantle wall thickness as occurs during growth. To test this prediction, we compared D. pealeii hatchlings and adults. Videography and morphometric analyses were used in tandem to measure dimensional changes in the mantle of hatchlings; similar data were collected from adults using sonomicrometry. These experiments revealed that (1) hatchlings experienced a gradient of strain and strain rate; (2) for hatchlings, the magnitude of the gradient of strain increased as jet amplitude increased, but unlike adults, the gradient of strain rate did not increase with increasing jet amplitude; (3) and the magnitude of the gradient of strain and strain rate increased with increasing relative mantle wall thickness. These findings challenge current theories of striated muscle function and call for a reanalysis of the evolution of muscle structure and function in cylindrical muscular organs.