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Effective cardiac pumping is critical to supply oxygen for all physiological functions and is a primary determinant of a fish’s upper thermal tolerance. This project will focus on mechanisms that account for the failure of the fish heart at high temperature and the large discrepancy for maximum heart rate that exists between fishes. The work is guided by the emergence of numerous studies showing that fish are either being threatened by increased water temperature or have relocated to cooler habitats globally. Irregular heartbeats are associated with cardiorespiratory collapse at supraoptimal temperatures and because heart rate reaches an absolute maximum near the optimal temperature in fishes, two hypotheses will be tested to determine the mechanistic underpinning for this limitation. The first proposes that the limitation lies with the cells of the cardiac pacemaker and the second posits that excitation-contraction coupling in the ventricle ultimately cannot keep up with pacemaker rate. These hypotheses will be tested using electrophysiology in single cells, optical mapping of the whole isolated heart; and in vivo measurements using echocardiography combined with ECG to identify other failings of integrated cardiac function in vivo. The student will be based in Manchester but will be encouraged to spend part of the degree working with other leaders in the field of comparative cardiac physiology. The opportunity to work in a consortium of labs will provides diverse and expert mentorship for development as a scientist. This PhD project is at the forefront of research on fish cardiac physiology and directly relevant to UK and global environmental concerns.
1. Vornanen, M., J. Haverinen, and S. Egginton, Acute heat tolerance of cardiac excitation in the brown trout (Salmo trutta fario). J Exp Biol, 2014. 217(Pt 2): p. 299-309.
2. Anttila, K., et al., Atlantic salmon show capability for cardiac acclimation to warm temperatures. Nat Commun, 2014. 5.
3. Eliason, E.J., et al., Differences in thermal tolerance among sockeye salmon populations. Science, 2011. 332(6025): p. 109-12.
4. Shiels, H.A., et al., Warm fish with cold hearts: thermal plasticity of excitation-contraction coupling in bluefin tuna. Proceedings of the Royal Society B: Biological Sciences, 2011. 278(1702): p. 18-27.
Globally, aquatic ecosystems face the localized and broad-scale influence of climate change. The 2012 UK Climate Change Risk Assessment predicts that by 2080 the average UK summer temperature could be 1-8 °C warmer and accompanied by more frequent extreme rainfall and drought events. Two obvious problems are expected to occur as a result of these forecasts: changes in water flow and increases in water temperature. This PhD project will combine field, lab and computational approaches to integrate the energetic physiology of the brown trout (Salmo Trutta) with temperature and shade cover in key sites within the 860 square mile Ribble River Catchment in the Northwest of England.
The PhD proposal stems from a partnership between the University of Manchester (UoM) and the Ribble Rivers Trust (RRT) and builds upon current work between institutions. The RRT is a science-led river restoration charity that, together with the Environment Agency (EA), developed an award winning climate change, mitigation and adaptation project called - Keeping Rivers Cool. This project plants trees to create shade to help maintain current water temperatures in anticipation of rises associated with climate change. Under the direction of RRT and UoM the student will learn GIS to manipulate the large high resolution 3D data set of tree shade provided by the EA for the Ribble catchment. The student will identify areas of varying relative shade to test the predictions of the model with respect to water temperature, shade and fish abundance. The student will work together with RRT’s fisheries scientists to conduct robust and cost-effective riverine surveys of sites specified through the computational work. Data loggers will be implanted in keys sites before and after tree planting. These sites will be monitored for fish abundance and the influence of trees. In the laboratory at UoM, the student will conduct energetic and kinematic studies on swimming brown trout to reveal mechanisms underlying physiological limitations to performance in warming rivers with variable flows. The expected outputs of this PhD are to provide a framework that the RRT can utilise to ensure its improvement and restoration projects are effective whilst providing the student with robust field, lab and computing skills in fish environmental physiology.
The vertebrate heart has evolved from the 2 chambered fish heart to the 4 chambered mammalian/bird heart. Associated with the change in chamber morphology are important changes in heart how the output of the heart is regulated. Cardiac output in fish, amphibians and reptiles is increased, to a large extent, by changing the volume of blood pumped by the heart. This means their hearts are regulated by stretch dependent mechanisms. In contrast birds and mammals tend modulate cardiac output via frequency, increasing the heart rate, rather than volume. Indeed, the fish and turtle hearts can expand more than 300% to accommodate large changes in blood volume whereas birds and mammals can increase heart rate 600%. At the level of the cardiac myocyte, the cells from birds more closely resemble those of reptiles than those of mammals. Thus, birds occupy a unique position in the evolution of vertebrate cardiac design. Their hearts are capable of cardiac performance on par, or exceeding, that of mammals, but are made up of myocytes that are morphologically similar to reptiles and fish. This PhD project will provide the first detailed investigation into the bird heart and its position within vertebrates. The student will learn in vivo measurements of cardiac function, mechanical and electrical studies of isolated whole hearts and cardiac myocytes. By incorporating in vivo measurements, electrophysiology, florescent imaging and molecular biology the student will apply techniques at the forefront of cardiology and zoological research. Thus this PhD has both evolutionary and biomedical relevance.
The sarcoplasmic reticulum (SR) is an intracellular Ca store in the myocytes that make up the heart. It is crucial for contraction and relaxation of the mammalian heart, but its role in other vertebrate classes is equivocal. Recent evidence suggests differences in SR function across species may have an underlying structural basis. Moreover, studies are emerging that show this Ca store acts as a safety mechanism in ectotherm hearts during environmental stress. This PhD Project explores the role of the SR in fish, reptiles, birds and mammals and how it is utilized to maintain cardiac function during stresses such as temperature, pH and hypoxia. The student will learn cardiac electrophysiology, florescent imaging and molecular biology - techniques at the forefront of cardiology and zoological research. Thus this PhD has both evolutionary and biomedical relevance and will provide novel insight into the evolution of cardiac design and function in vertebrates.
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