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1. Fishes can use axial muscles as anchors or motors for powerful suction feeding

   https://doi.org/10.1242/jeb.225649  

   Camp, Ariel L. ; Olsen, Aaron M. ; Hernandez, L. Patricia ; Brainerd, Elizabeth L. ( September 2020 , The Journal of Experimental Biology)

   ABSTRACT Some fishes rely on large regions of the dorsal (epaxial) and ventral (hypaxial) body muscles to power suction feeding. Epaxial and hypaxial muscles are known to act as motors, powering rapid mouth expansion by shortening to elevate the neurocranium and retract the pectoral girdle, respectively. However, some species, like catfishes, use little cranial elevation. Are these fishes instead using the epaxial muscles to forcefully anchor the head, and if so, are they limited to lower-power strikes? We used X-ray imaging to measure epaxial and hypaxial length dynamics (fluoromicrometry) and associated skeletal motions (XROMM) during 24 suction feeding strikes frommore »three channel catfish ( Ictalurus punctatus ). We also estimated the power required for suction feeding from oral pressure and dynamic endocast volume measurements. Cranial elevation relative to the body was small (<5 deg) and the epaxial muscles did not shorten during peak expansion power. In contrast, the hypaxial muscles consistently shortened by 4–8% to rotate the pectoral girdle 6–11 deg relative to the body. Despite only the hypaxial muscles generating power, catfish strikes were similar in power to those of other species, such as largemouth bass ( Micropterus salmoides ), that use epaxial and hypaxial muscles to power mouth expansion. These results show that the epaxial muscles are not used as motors in catfish, but suggest they position and stabilize the cranium while the hypaxial muscles power mouth expansion ventrally. Thus, axial muscles can serve fundamentally different mechanical roles in generating and controlling cranial motion during suction feeding in fishes.« less
2. What Fish Can Teach Us about the Feeding Functions of Postcranial Muscles and Joints

   https://doi.org/10.1093/icb/icz005  

   Camp, Ariel L ( April 2019 , Integrative and Comparative Biology)

   Abstract Studies of vertebrate feeding have predominantly focused on the bones and muscles of the head, not the body. Yet, postcranial musculoskeletal structures like the spine and pectoral girdle are anatomically linked to the head, and may also have mechanical connections through which they can contribute to feeding. The feeding roles of postcranial structures have been best studied in ray-finned fishes, where the body muscles, vertebral column, and pectoral girdle attach directly to the head and help expand the mouth during suction feeding. Therefore, I use the anatomy and motion of the head–body interface in these fishes to develop amore »mechanical framework for studying postcranial functions during feeding. In fish the head and body are linked by the vertebral column, the pectoral girdle, and the body muscles that actuate these skeletal systems. The morphology of the joints and muscles of the cranio-vertebral and hyo-pectoral interfaces may determine the mobility of the head relative to the body, and ultimately the role of these interfaces during feeding. The postcranial interfaces can function as anchors during feeding: the body muscles and joints minimize motion between the head and body to stabilize the head or transmit forces from the body. Alternatively, the postcranial interfaces can be motors: body muscles actuate motion between the head and body to generate power for feeding motions. The motor function is likely important for many suction-feeding fishes, while the anchor function may be key for bite- or ram-feeding fishes. This framework can be used to examine the role of the postcranial interface in other vertebrate groups, and how that role changes (or not) with morphology and feeding behaviors. Such studies can expand our understanding of muscle function, as well as the evolution of vertebrate feeding behaviors across major transitions such as the invasion of land and the emergence of jaws.« less
3. Evaluate the Effect of Seat Back Restriction on Head, Neck and Torso Responses of Front Seat Occupants when Subjected to a Moderate Speed Rear-Impact

   https://doi.org/10.4271/2021-01-0920  

   Ramachandra, R. ; Pradhan, V. ; Kang, Y. ; Davidson, R. ; Humer, M. ; Zhang, J. ( April 2021 , SAE technical paper series)

   During high-speed rear impacts with delta-V > 25 km/h, the front seats may rotate rearward due to occupant and seat momentum change leading to possibly large seat deflection. One possible way of limiting this may be by introducing a structure that would restrict large rotations or deformations, however, such a structure would change the front seat occupant kinematics and kinetics. The goal of this study was to understand the influence of seat back restriction on head, neck and torso responses of front seat occupants when subjected to a moderate speed rear-impact. This was done by simulating a rear impact scenariomore »with a delta-V of 37.4 km/h using LS-Dyna, with the GHBMC M50 occupant model and a manufacturer provided seat model. The study included two parts, the first part was to identify worst case scenarios using the simplified GHBMC M50-OS, and the second part was to further investigate the identified scenarios using the detailed GHBMC M50-O. The baseline condition included running the belted GHBMC on the seat at the specified pulse. This was followed by including a seatback constraint, a restriction bar, at 65 mm from the seat back to restrict rearward movement. Four different scenarios were investigated using the GHBMC M50-OS for the first part of the study both in the baseline and inclusion of a restriction bar behind the seatback: occupant seated normally; occupant offset on the seat; occupant rotated on the seat; and occupant seated normally but at a slightly oblique rear impact direction. The oblique condition was identified as the worst-case scenario based on the inter-vertebral kinematics; therefore, this condition was further investigated in the simulations with GHBMC M50-O. In the oblique rear impact scenario, the head missed the head restraint leading to inter-vertebral rotations exceeding the physiological range of motions regardless of the restriction bar use. However, adding a restriction bar behind the seat back showed a higher HIC and BrIC in both normal and oblique pulses due to the sudden stop, although the magnitudes were below the threshold.« less
4. Heterochronic Shifts Mediate Ecomorphological Convergence in Skull Shape of Microcephalic Sea Snakes

   https://doi.org/10.1093/icb/icz033  

   Sherratt, Emma ; Sanders, Kate L ; Watson, Amy ; Hutchinson, Mark N ; Lee, Michael S ; Palci, Alessandro ( May 2019 , Integrative and Comparative Biology)

   Abstract Morphological variation among the viviparous sea snakes (Hydrophiinae), a clade of fully aquatic elapid snakes, includes an extreme “microcephalic” ecomorph that has a very small head atop a narrow forebody, while the hind body is much thicker (up to three times the forebody girth). Previous research has demonstrated that this morphology has evolved at least nine times as a consequence of dietary specialization on burrowing eels, and has also examined morphological changes to the vertebral column underlying this body shape. The question addressed in this study is what happens to the skull during this extreme evolutionary change? Here wemore »use X-ray micro-computed tomography and geometric morphometric methods to characterize cranial shape variation in 30 species of sea snakes. We investigate ontogenetic and evolutionary patterns of cranial shape diversity to understand whether cranial shape is predicted by dietary specialization, and examine whether cranial shape of microcephalic species may be a result of heterochronic processes. We show that the diminutive cranial size of microcephalic species has a convergent shape that is correlated with trophic specialization to burrowing prey. Furthermore, their cranial shape is predictable for their size and very similar to that of juvenile individuals of closely related but non-microcephalic sea snakes. Our findings suggest that heterochronic changes (resulting in pedomorphosis) have driven cranial shape convergence in response to dietary specializations in sea snakes.« less
5. Royal knifefish generate powerful suction feeding through large neurocranial elevation and high epaxial muscle power

   https://doi.org/10.1242/jeb.244294  

   Li, Ellen Y. ; Kaczmarek, Elska B. ; Olsen, Aaron M. ; Brainerd, Elizabeth L. ; Camp, Ariel L. ( June 2022 , Journal of Experimental Biology)

   ABSTRACT Suction feeding in ray-finned fishes involves powerful buccal cavity expansion to accelerate water and food into the mouth. Previous XROMM studies in largemouth bass (Micropterus salmoides), bluegill sunfish (Lepomis macrochirus) and channel catfish (Ictalurus punctatus) have shown that more than 90% of suction power in high performance strikes comes from the axial musculature. Thus, the shape of the axial muscles and skeleton may affect suction feeding mechanics. Royal knifefish (Chitala blanci) have an unusual postcranial morphology, with a ventrally flexed vertebral column and relatively large mass of epaxial muscle. Based on their body shape, we hypothesized that royal knifefishmore »would generate high power strikes by utilizing large neurocranial elevation, vertebral column extension and epaxial shortening. As predicted, C. blanci generated high suction expansion power compared with the other three species studied to date (up to 160 W), which was achieved by increasing both the rate of volume change and the intraoral subambient pressure. The large epaxial muscle (25% of body mass) shortened at high velocities to produce large neurocranial elevation and vertebral extension (up to 41 deg, combined), as well as high muscle mass-specific power (up to 800 W kg−1). For the highest power strikes, axial muscles generated 95% of the power, and 64% of the axial muscle mass consisted of the epaxial muscles. The epaxial-dominated suction expansion of royal knifefish supports our hypothesis that postcranial morphology may be a strong predictor of suction feeding biomechanics.« less