A Development Series of the Soft Sculpin Psychrolutes sigalutes

The development of larval fishes is a chronically understudied, critically important field, which offers broad insight into a defining period in the life history of fishes. Examinations of development shed light on the behavior and ecology of fishes at a stage wherein they are difficult to observe directly. We cleared and stained 36 specimens of the soft sculpin, Psychrolutes sigalutes, in an effort to link morphological development to preexisting studies on their behavioral shifts with growth. Rapid development of feeding structures suggests a fish that quickly grows into a highly capable hunter, well-suited to its lengthy transitional feeding period in the plankton. Given the intense focus of development on hunting, we believe that transforming P. sigalutes may be the apex predators in their habitat, possibly responsible for the top-down control of local ichyhtoplankton

Studying the Force-Length Relationship in the Adductor Mandibulae of Pink and King Salmon

Specialized feeding behavior is generally reflected not only in skeletal anatomy (as has been the major focus of functional morphology literature) but also in muscular morphology and physiology. We show that this is the case for salmon feeding mechanics of king and pink salmon. King salmon (Oncorhynchus tshawytscha) eat small, fast fish; and pink salmon (Oncorhynchus gorbuscha) primarily filter feed on planktonic organisms by keeping their mouths open while swimming. Salmon close their jaws using the adductor mandibulae, which, like all skeletal muscles, is constrained by a strict relationship between muscle length and force. Muscles that are over-stretched or overshortened exert weaker forces than they do at optimal length, and muscle length corresponds to gape. We compared the force-length curves of king and pink salmon adductor mandibulae and demonstrated that the maximum bite force of king salmon is achieved closer to maximum gape (67% of max gape, n = 3). This may allow them to take advantage of optimal muscle length, and thus greater force production, when eating large or elusive prey. In pink salmon, the force-length curve is centered at a smaller relative gape, closer to mid-gape (43% of max gape, n = 6). This may facilitate filter feeding, allowing reasonably high forces at a range of medium gape sizes. The different feeding preferences of these species may have put different pressures on the evolution of jaw muscle physiology, resulting in distinct optimal solutions to the force-length constraint

Five Fishes, Five Faces: Comparative Functional Morphology of the Feeding Apparatus in Sculpins (Cottoidea)

By studying variation in feeding apparatus morphology across similar sympatric species, we can better understand the evolutionary relationships and ecological niches of these species. The most common feeding technique among vertebrates is suction feeding, in which an animal rapidly expands its buccal cavity to create negative pressure and suck in prey. Suction feeders not only open their jaws quickly; they must also close them rapidly to prevent elusive prey from escaping. In this study, we compared jaw morphology and feeding kinematics of five species of Salish Sea sculpin. We used anatomical dissection to measure differences in jaw adductor morphology and jaw leverage, and we used Sonometric crystal implantation to measure gape change and muscle strain during feeding. Although we found high conservation of body length to muscle mass ratio among species, visual inspection of the head and jaw revealed important differences. We found that the red Irish lord (Hemilepidotus hemilepidotus) possessed the fastest jaw, as demonstrated by anatomical measurement of a small lever ratio, kinematic measurement of a large gape-change to muscle-strain ratio, and behavioral observation of the red Irish lord’s ambush hunting strategy. This study highlights the importance of including behavior and ecology in analyses of organismal morphology

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

Five Fishes, Five Faces: Comparative Functional Morphology of the Feeding Apparatus in Sculpins (Cottoidea)

By studying variation in feeding apparatus morphology across similar sympatric species, we can better understand the evolutionary relationships and ecological niches of these species. The most common feeding technique among vertebrates is suction feeding, in which an animal rapidly expands its buccal cavity to create negative pressure and suck in prey. Suction feeders not only open their jaws quickly; they must also close them rapidly to prevent elusive prey from escaping. In this study, we compared jaw morphology and feeding kinematics of five species of Salish Sea sculpin. We used anatomical dissection to measure differences in jaw adductor morphology and jaw leverage, and we used Sonometric crystal implantation to measure gape change and muscle strain during feeding. Although we found high conservation of body length to muscle mass ratio among species, visual inspection of the head and jaw revealed important differences. We found that the red Irish lord (Hemilepidotus hemilepidotus) possessed the fastest jaw, as demonstrated by anatomical measurement of a small lever ratio, kinematic measurement of a large gape-change to muscle-strain ratio, and behavioral observation of the red Irish lord’s ambush hunting strategy. This study highlights the importance of including behavior and ecology in analyses of organismal morphology

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

Localization of magnetic pills

Numerous therapeutics demonstrate optimal absorption or activity at specific sites in the gastrointestinal (GI) tract. Yet, safe, effective pill retention within a desired region of the GI remains an elusive goal. We report a safe, effective method for localizing magnetic pills. To ensure safety and efficacy, we monitor and regulate attractive forces between a magnetic pill and an external magnet, while visualizing internal dose motion in real time using biplanar videofluoroscopy. Real-time monitoring yields direct visual confirmation of localization completely noninvasively, providing a platform for investigating the therapeutic benefits imparted by localized oral delivery of new and existing drugs. Additionally, we report the in vitro measurements and calculations that enabled prediction of successful magnetic localization in the rat small intestines for 12 h. The designed system for predicting and achieving successful magnetic localization can readily be applied to any area of the GI tract within any species, including humans. The described system represents a significant step forward in the ability to localize magnetic pills safely and effectively anywhere within the GI tract. What our magnetic pill localization strategy adds to the state of the art, if used as an oral drug delivery system, is the ability to monitor the force exerted by the pill on the tissue and to locate the magnetic pill within the test subject all in real time. This advance ensures both safety and efficacy of magnetic localization during the potential oral administration of any magnetic pill-based delivery system

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

Feeding Mechanics and Functional Morphology in the Jaws of Sculpins

Species with overlapping geographic ranges, similar morphology, and ecological roles often vie for the same resources and therefore face competitive exclusion. This competition can be reduced if species vary in skeletal and muscular anatomy, because it changes biomechanical performance across species. We examined biomechanical variation of feeding structures in a group of nineteen sculpins (Cottoidea) that co-occur in the marine habitat around the San Juan Islands. We quantified evolutionary correlations of skeletal morphology and muscle morphology by conducting phylogenetic independent contrasts using a phylogeny constructed from published molecular data. We hypothesized that skeletal leverage (mechanical advantage) and muscle architecture (gearing) could either display a positive evolutionary correlation (changing over evolutionary time to perform inversely of each other), or the features could display a negative correlation (changing over evolutionary time to perform in the same way). We found a positive correlation between evolutionary shifts of out-lever length and adductor muscle length, but no correlation between evolutionary shifts of in-lever length and adductor muscle length or adductor muscle length and lever ratio. Our results demonstrate that skeletal leverage and muscle architecture evolve independently in individual species of sculpins. These results also suggest that these two functional units (skeletal morphology and muscle morphology) both contribute to biomechanical diversity in closely related, geographically co-occurring sculpin species, indicating their importance as metrics of ecomorphological diversity

Determinants of aponeurosis shape change during muscle contraction

Aponeuroses are sheet-like elastic tendon structures that cover a portion of the muscle belly and act as insertion sites for muscle fibers while free tendons connect muscles to bones. During shortening contractions, free tendons are loaded in tension and lengthen due to the force acting longitudinally along the muscle׳s line of action. In contrast, aponeuroses increase in length and width, suggesting that aponeuroses are loaded in directions along and orthogonal to the muscle׳s line of action. Because muscle fibers are isovolumetric, they must expand radially as they shorten, potentially generating a force that increases aponeurosis width. We hypothesized that increases in aponeurosis width result from radial expansion of shortening muscle fibers. We tested this hypothesis by combining in situ muscle-tendon measurements with high-speed biplanar fluoroscopy measurements of the turkey׳s lateral gastrocnemius (n=6) at varying levels of isotonic muscle contractions. The change in aponeurosis width during periods of constant force depended on both the amount of muscle shortening and the magnitude of force production. At low to intermediate forces, aponeurosis width increased in direct proportion to fiber shortening. At high forces, aponeurosis width increased to a lesser extent or in some cases, decreased slightly during fiber shortening. Our results demonstrate that forces generated from radial expansion of shortening muscle fibers tend to drive increases in aponeurosis width, whereas longitudinal forces tend to decrease aponeurosis width. Ultimately, it is these two opposing forces that drive changes in aponeurosis width and alter series elastic stiffness during a muscle contraction