Research Interests
My research addresses the fundamental question of how the cardiorespiratory system of animals has evolved to meet metabolic demands. Metabolism is a biological process that can control and contain fierce combustion between organic substrate and oxygen. When the substrate is in plentiful supply, the regulation of oxygen supply becomes vital to sustaining the fire of life, just like a fire stove. The cardiorespiratory system is a vital part of oxygen transport cascade that regulates the flux of oxygen from the external environment to mitochondria where ATP is produced.
Using such an integrated physiological system and with a focus on the cardiorespiratory system, I study an integrated respiratory metabolic phenotype of multiple fish species in warm temperature, low oxygen and viral infections. The three environmental variables are likely to be major selection forces that impact the survival and growth of the wild fish populations in a changing climate. Meanwhile, the environmental variables affect all activities of animals through metabolism. Deciphering the impacts of these environmental factors using a comparative approach will advance the understanding of how the cardiorespiratory system of animals has evolved to meet the metabolic demands.
Integrated Respiratory Assessment Paradigm (IRAP)
The whole-animal performance of cardiorespiratory robustness is measured as the capability of acquiring oxygen (e.g. rate of oxygen uptake) in a variety of physiological states. These include maximum exercise performance, capability to recover to a quiescent state, minimum maintenance metabolic rate and capability to perform anaerobic tasks. Rate of oxygen uptake, in this regard, becomes a proxy of whole-animal metabolic rate, because of the fixed stoichometry of respiratory gas exchange. Using this principle, I developed and validated an integrated respiratory assessment paradigm (IRAP) to encompass the quantifications of respiratory metabolic traits in a high-throughput manner in a higher accuracy. Collectively, IRAP measures metabolic capacity, including the scope for aerobic and anaerobic metabolism for a comprehensive evaluation of physiological robustness.
A Selection of the Projects
Impacts of Viral Infections on the Respiratory Phenotype
Metabolic respiratory performance under viral infection could be an overlooked yet major force for natural selection in fish. Piscine orthoreovirus (PRV) targets erythrocytes for principal replication and infections can develop into heart inflammation in some instances. On the contrary, infectious hematopoietic necrosis virus (IHNV) infection triggers metabolic suppression of energetically demanding processes, such as cell proliferation and protein synthesis, after the initial rapid anti-virus responses. Hence, I use IRAP to test the hypothesis that PRV infection limits metabolism, while IHNV infection masks metabolism, using Atlantic salmon (Salmo salar) and sockeye salmon (Oncorhynchus nerka) as model species.
Collective movements of vertebrates
Bioenergetics and biomechanics of fish schooling
Collective movement is a ubiquitous behaviour among vertebrates. It involves active, directional forward movement where animals move as a group along a common mean trajectory. We demonstrated a concave upward-shaped metabolism–speed curve, with a minimum metabolic cost at ∼1 body length per second, the average migratory speed of fish species. We discovered that fish schools reduce total energy expenditure (TEE) per tail beat by up to 56% compared to solitary fish. When reaching their maximum sustained swimming speed, fish swimming in schools had a 44% higher maximum aerobic performance and used 65% less non-aerobic energy compared to solitary individuals, which lowered the TEE and total cost of transport by up to 53%, near the lowest recorded for any aquatic organism. Furthermore, we demonstrated a novel turbulence sheltering hypothesis that collective movements of fish schools in turbulent flow can reduce the total energetic cost of locomotion by shielding individuals from the perturbation of chaotic turbulent eddies.
Pioneer high-resolution characterizations of aerobic and anaerobic contributions for locomotion
Maximum oxygen uptake & Excess post-exercise oxygen consumption
Aerobic capacity is widely used to evaluate human cardiorespiratory fitness, to assess ecological performance in ectotherms, and to study the divergent evolution of cardiorespiratory systems. In an earlier commentary, my research had suggested better precision and accuracy were needed to measure maximum oxygen uptake (ṀO2max), and hence aerobic capacity in fishes. The J. Exp. Biol. paper did just that. I developed, validated and applied an innovative iterative algorithm that generated a 23% more accurate estimate of ṀO2max. The algorithm is now available in the R programming language. This work appeared in the most impactful experimental biology journal that has a broad readership among physiologists and ecologists. As a further advance, I developed a new experimental protocol to avoid missing the peak values and increase the accuracy by 31%. With this new measurement precision, I am poised to link the dynamics ṀO2 and kinematics for my post-doctoral research.
Modelling curvilinear effects of climate change related stressors on functional biology
Warmer ocean & less oxygen
The warmer ocean also contains less amount of dissolved oxygen. Aquatic ectotherms have a body temperature that closely matches the ambient temperature of the environment. Although the ectotherms have an optimal thermal range for performance, the thermal performance curve shows an impressive degree of intra-specific variations. At each temperature, partial pressure of oxygen can also vary, and a declining temperature limits the performance of ectotherms. While the limiting effect of oxygen on aquatic ectoderms is a major tenet in physiology and ecology, the validation of a reliable approach to quantify a hypoxic performance curve is established. A better understanding of the inter-specific variations of the thermal performance curve, and a better tool to quantify the hypoxic performance curve not only inspires more interesting questions in the research in functional biology, but also better inform the conservation policy.
Thermal performance curve
