Use the Force: scaling of jaw muscle forces in the great sculpin, Myoxocephalus polyacanthocephalus

Suction feeding is the most common vertebrate feeding mode. Fishes suction feed by rapidly expanding the buccal cavity, creating a subambient pressure inside the mouth that causes water (and, ideally, a prey item) to rush in. The predator’s ability to close the mouth around evasive prey determines feeding success. As a fish grows, the volume it engulfs should scale with length to the third power (volume ∝ length3). This becomes a burden on larger fishes, as muscle force (which drives mouth closing) should scale with length squared (force ∝ muscle cross-sectional area ∝ length2). Since suction volume increases faster with size than muscle force, a force deficit results as fish grow larger. Previous studies show that great sculpin counter the force deficit with increased jaw leverage and more force production at longer fish lengths. In this study, we examined muscle force and muscle strain variation across sizes in the suction- feeding great sculpin, Myoxocephalus polyacanthocephalus. Because muscles are subject to the limitations of the length-tension relationship, we saw maximum force (P0) production at intermediate muscle lengths (L0) and declining forces at longer/shorter muscle lengths. Our results show that great sculpin maintain a constant amount of muscle strain to achieve at least 50% of their maximum force (P0) throughout ontogeny. As the great sculpin grows, it uses a wider range of this available muscle strain in feeding, stretching its muscles away from L0 and losing force in the process. Thus in addition to an increasing muscle force deficit, larger great sculpin experience declining jaw-closing forces due to the length-tension properties of jaw- closing muscles

Bigger, Stronger but Not Faster: ontogenetic change in the jaw biomechanics of the great sculpin, Myoxocephalus polyacanthocephalus

Suction feeding is the most common vertebrate feeding mode. Fishes suction feed by rapidly expanding the buccal cavity, creating a subambient pressure inside the mouth that causes water (and, ideally, a prey item) to rush in. The predator’s ability to close the mouth around evasive prey determines feeding success. As a fish grows, the volume it engulfs should scale with length to the third power (volume ∝ length3). This becomes a burden on larger fishes, as muscle force (which drives mouth closing) should scale with length squared (force ∝ muscle cross-sectional area ∝ length2). Since suction volume increases faster with size than muscle force, a force deficit results as fish grow larger. Two ways to counteract this deficit are to increase muscle mass or increase skeletal leverage within the jaw. In this study, we examined musculoskeletal variation in anatomy and kinematics across an ontogenetic series in the suction-feeding great sculpin, Myoxocephalus polyacanthocephalus. Our results show that great sculpin mandibles change shape as they grow, increasing jaw-closing muscle leverage, which counters the force deficit (N = 6, p = 0.0456). Kinematic results agree: a given amount of muscle strain produces less jaw displacement in larger fish (N = 6, p > 0.00015). We did not find disproportionate changes in muscle mass with size (N = 7, p=.514). Smaller fish, therefore, rely on high-velocity jaw closing whereas larger fish rely more on high forces to close the jaw. We hypothesize that a smaller fish needs high speed to reduce the risk of prey escape from a small suction volume, whereas a large fish needs high forces to move the disproportionately large volume of water

Bigger, Stronger but Not Faster: ontogenetic change in the jaw biomechanics of the great sculpin, Myoxocephalus polyacanthocephalus

Suction feeding is the most common vertebrate feeding mode. Fishes suction feed by rapidly expanding the buccal cavity, creating a subambient pressure inside the mouth that causes water (and, ideally, a prey item) to rush in. The predator’s ability to close the mouth around evasive prey determines feeding success. As a fish grows, the volume it engulfs should scale with length to the third power (volume ∝ length3). This becomes a burden on larger fishes, as muscle force (which drives mouth closing) should scale with length squared (force ∝ muscle cross-sectional area ∝ length2). Since suction volume increases faster with size than muscle force, a force deficit results as fish grow larger. Two ways to counteract this deficit are to increase muscle mass or increase skeletal leverage within the jaw. In this study, we examined musculoskeletal variation in anatomy and kinematics across an ontogenetic series in the suction-feeding great sculpin, Myoxocephalus polyacanthocephalus. Our results show that great sculpin mandibles change shape as they grow, increasing jaw-closing muscle leverage, which counters the force deficit (N = 6, p = 0.0456). Kinematic results agree: a given amount of muscle strain produces less jaw displacement in larger fish (N = 6, p > 0.00015). We did not find disproportionate changes in muscle mass with size (N = 7, p=.514). Smaller fish, therefore, rely on high-velocity jaw closing whereas larger fish rely more on high forces to close the jaw. We hypothesize that a smaller fish needs high speed to reduce the risk of prey escape from a small suction volume, whereas a large fish needs high forces to move the disproportionately large volume of water