Meeting Abstract
Skulls are astoundingly diverse, and anatomy, kinematics, and muscle physiology collectively determine the biomechanical implications of this diversity. An often-overlooked variable is physiological muscle length: force declines as muscle is stretched or shortened and force is optimal at an intermediate length, so jaw-closing force is dictated by the adductor muscle’s length. Recent empirical data support the notion that muscle length is important for understanding function. Snail size, for example, dictates gape in the molluscivorous black carp (Mylopharyngodon piceus); since gape dictates muscle length, which dictates muscle force, prey size has an overriding effect on the force available for crushing, and thus crushing performance. Jaw movement patterns dictate the gape:muscle length relationship; grass carp (Ctenopharyngodon idella) use more jaw rotation than black carp when chewing, and the high muscle strains that drive this rotation result in muscle force loss of up to 80%. The gape:muscle length relationship also changes through ontogeny; since muscle force and suction volume scale differently with size, larger fish face a force deficit when closing the mouth around an engulfed volume of water. In great sculpin (Myoxacephalus polyacanthocephalus), this deficit is counteracted by ontogenetic changes in jaw lever ratio, resulting in lower gear ratios (jaw movement/muscle length change) at larger sizes. Across species of sculpin, gape:muscle length relationships co-evolve with changes in fiber length, so that muscle strain magnitude remains relatively constant and low across phylogeny. The simple relationship between muscle length and gape distills important aspects of anatomy, in vivo kinematics, and muscle physiology that provide vital insight into the functional diversity of feeding mechanisms.
