Do fish have necks: measuring 3D motion of the vertebrae and axial muscle dynamics in suction-feeding fishes.

I will demonstrate how muscles and bones work together to give humans and animals a flexible neck, by studying the hidden "neck" of fish. A neck allows the head to move three-dimensionally, and independently of the limbs and body. Its importance in humans is starkly illustrated by the functional deficits imposed by disorders of the neck, and its origin was a major transformation that spurred the evolution of land-dwelling vertebrates. Yet we know relatively little of how the bones and muscles of the neck interact to provide these essential functions, because their structure and motions are complex and have been impossible to directly visualize or separate from motions of the head and body. With new imaging techniques it is now possible to measure bone and muscle motion in 3D, and fish offer anintriguing model system for investigating these questions. Although fish lack a true, anatomical neck, studies of their feeding suggest the backbone could function as a neck by bending upwards to lift the head away from the body.
If fish do have a hidden "neck", it is powered by the body muscles, which extend from head to tail in a complex architecture of muscle fibres. All muscles have a trade-off between how fast they can shorten and how much force they can produce. The orientation of the body muscle fibres and the way that changes as they shorten could allow the muscle to "shift gears" and shorten at different speeds, depending on the force required. This dynamic gearing can occur in human muscles, and may contribute to age-related changes in muscle performance. Directly measuring dynamic fibre orientation and shortening has been very challenging, but new methods for visualizing muscle fibres and measuring their motion may provide key insights into muscle function.
I will measure the 3D bending of the backbone in fish and its role in moving the head three-dimensionally and independently of the shoulder girdle and body. I will also examine the architecture and dynamic gearing of the body muscles in this neck region to establish how fibre re-orientation impacts muscle performance.
I will carry out this research at the University of Liverpool, using new, X-ray based visualizations to measure 3D bone and muscle motion in three fish with a range of vertebral shapes and hypothesized "neck bending". This work builds on my experience using and developing such 3D imaging tools, and utilizes the University's world-class X-ray filming facility. X-ray video of each fish's head, shoulder girdle, and backbone will be matched with 3D models of these bones, built from CT scans, to create an accurate 3D animation from which I can measure each bone's motion. From these X-ray videos, I will also measure how the body muscles change length and shape during neck motion. By learning contrast-enhanced micro-CT scanning techniques from Dr. Nathan Jeffrey, I can visualize the 3D arrangement of the body muscle fibres. Working with Dr. Karl Bates and Kris D'Aout, I will use these images to add virtual muscle fibres to the bone animations: creating a model of how fibre orientation and muscle shape change affects muscle shortening.
The proposed research will change our perspective on the origin of the neck, and provide insights into muscle dynamics. By linking the anatomy and motion of the backbone in living fish, this study will lay the foundation for understanding how the neck may have evolved. It will also help aquaculturists understand and improve feeding performance in commercial trout. My data on shape changes, fibre rotation and shortening of fish muscles can be applied to understanding how human muscles undergo these same dynamics-and how changes these dynamics during ageing may impact health and performance. Lastly, I will use the engaging 3D models, animations, and X-ray videos from this research in outreach programs at the World Museum in Liverpool and local science clubs to inspire the next generation of scientists and innovators.

I will show that the vertebral column of fish can function as a neck: generating three-dimensional and independent motion of the head, powered by the dorsal (epaxial) body muscles. The neck is a defining evolutionary transformation in terrestrial tetrapods, but its biomechanics and evolution are poorly understood. Fish lack an anatomical neck, but the anterior vertebrae may flex dorsally during feeding. This neck-like motion must be powered by the epaxials, whose complex fibre orientations may allow 3D changes in muscle shape and fibre rotations. This may decouple fibre-shortening and whole-muscle shortening during dorsal flexion, acting as a gear to optimize trade-offs between muscle force and velocity.
I will use new, 3D visualization tools to determine whether the anterior vertebrae of fish function as a neck, and how the architecture and dynamic gearing of the epaxial muscles generate these neck-like motions. I will study 3 fish hypothesized to have moderate (trout, Oncorhyncus mykiss) or extreme (frogfish, Antennarius hispidus, and pikehead, Luciocephalus pulcher) "neck bending". Skeletal motions will be measured with X-Ray Reconstruction of Moving Morphology, which combines biplanar X-ray video with 3D morphology from computed tomography (CT) scans to create accurate 3D animations of bone motion. Muscle shortening measured from these X-ray videos will be used with 3D muscle fibre architecture from contrast-enhanced micro-CT scans and the XROMM animations to create a musculoskeletal model. With this model, I can link muscle fibre orientation, rotation, and shape changes to shortening velocity, and ultimately performance.
This research will transform our understanding of the vertebrae and body muscles in fishes, with implications for the origin and mechanics of neck motion in tetrapods, and improve our understanding of dynamic muscle gearing and how changes in this architecture during ageing will impact performance.

The proposed research will have medium-to-long-term benefits for healthcare and for economic performance, productivity and animal welfare in UK aquaculture, and immediate benefits for a local museum, public engagement, and education in the sciences.

My work will measure and model changes in 3D muscle shape and fibre orientation during a natural behaviour, helping us understand how these same muscle dynamics may lead to ageing-related changes in muscle performance. Human muscles decline in force and speed with age, leading to decreased strength and mobility. Recent work in animal models has linked a decline in muscle performance with alterations in the dynamic re-orientation of fibres within a muscle during movement. In healthy muscles, the whole muscle changes shape or "bulges", which decouples fibre shortening from whole-muscle shortening. This decoupling allows muscles to essentially switch gears: adjusting how much force and velocity they produce depending on what's required for the task. However, our understanding of this dynamic muscle gearing is severely limited by the lack of measurements from live muscles-either healthy or aged-during natural behaviours. Fish body muscles can be an excellent model system: these muscles are large, easily implanted with markers to monitor shape and length changes, isolated from other muscles, and lack external tendons (which can also influence muscle shortening). My research will image the 3D fibre architecture and shape changes of muscle and relate fibre orientation to muscle velocity and power production. These results will provide insights into the function of dynamic architecture and gearing of healthy muscles, crucial for researchers including those at IACD, seeking to understand and improve muscle performance and human health across all ages.

My research on fish vertebral structure and function will also lead to improved welfare of farmed fish and productivity of the UK's aquaculture industry. Salmon and rainbow trout (99% of UK farmed fish in 2012) have high rates of vertebral deformities when raised commercially. These deformities reduce the quality and value of the fish, and are a serious welfare concern. However, there is little known about the 3D motion of the spine in living healthy fish, especially during feeding. I will measure vertebral motion and its function in head mobility during feeding in rainbow trout, greatly improving our understanding of the spine's biomechanics. This will lead to improved detection and prevention of vertebral deformities in farmed fish, and therefore the economic productivity of the aquaculture industry. My work will also demonstrate how body muscles contribute to feeding performance, helping breeders select for 1) increased muscle growth and mass without compromising feeding efficiency and 2) increased feeding performance, particularly in larval fish, by selecting for faster development of the body muscles and vertebrae.

The visual products (bone models, animations, videos) of this interdisciplinary research will provide immediate benefits for the World Museum (Liverpool) and public engagement and education in the sciences. I will enrich the Museum's aquarium displays through an online exhibit of images, videos, and models that demonstrate fish anatomy and biomechanics, and an activity sheet for aquarium visitors. Throughout the fellowship I will also participate in public outreach events, using the captivating visuals from my research to engage visitors in biology, and also the physics, engineering, maths, and computer animations that my work relies on. This will lead to the development of educational materials for local student science clubs, which will use my research to introduce students to a range of STEM subjects, and enhance and encourage their science education.