Research Overview

The overarching goal of my research program is to understand the mechanisms and functional, ecological, and adaptive significance of physiological diversity among animals. My work considers the physiological variation that exists within individuals (i.e. acute reactions, phenotypic plasticity) as well as across populations, species, and broad phylogenetic boundaries (i.e. evolutionary).  Studying physiological diversity and its underlying mechanisms across these scales, in particular, provides insight into the vulnerability or tolerance of animals to environmental change, which can challenge organismal persistence by constraining function and performance. Much of my research, therefore, is directed at understanding the physiological responses that allow animals to maintain function and performance and thus persist in challenging environments, including exposure to abiotic, biotic, and anthropogenic stressors. Working mostly on fishes because of their biological and economic importance, I focus on two major, integrated physiological systems: energy metabolism, or how energy is supplied and used, and the cardiorespiratory system that sustains it. These are ideal systems in which to broadly explore the significance of physiological diversity because metabolism is fundamental to all life processes, and metabolic function is sensitive to many forms of environmental stress. My research involves comparative and experimental approaches incorporating biochemical, molecular, cellular, organ system, and organismal techniques. Ultimately, I aim to integrate physiology from cell to environment, to use physiology to assess and forecast the consequences for animals of anthropogenic impacts on the environment, and to understand the physiological linkages between environmental variability, organismal function and performance, and ecological and evolutionary patterns.
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Currently, I am carrying out projects to investigate:

• The physiological and behavioural mechanisms underlying winter dormancy in fishes
• Causes & consequences of overwintering strategies in fishes
• Physiological and behavioural responses to 'ocean acidification' in temperate and tropical fishes
• The physiological bases of variation in hypoxia tolerance among fishes
• The impacts of dietary preference and fasting on metabolic pathways in fishes and cephalopods
• The interactive effects of biotic stress (competition with invasive species) and abiotic stress (UV radiation, temperature) on physiological performance in amphibians and fishes
• The diversity and patterns of energy metabolism among vertebrates, including elasmobranchs​

Research Facilities

For metabolism to sustain life, energy supply must be matched to energy demand in order to attain metabolic energy balance and preserve cellular energy levels. The general thrust of my research program has been to investigate the ways in which fishes maintain metabolic energy balance in response to (a)biotic environmental variability as well as temporal organismal change (i.e. plasticity and evolutionary processes), both of which can alter the functions and capacities of energy supply or demand processes. Thus, I seek to understand: 

1. The integrated biochemical, molecular, and physiological mechanisms by which fishes maintain metabolic energy balance in order to successfully react, acclimate, and adapt to challenging and changing environments 
2. The environmental and evolutionary influences underlying the diversity of metabolic organization and fuel selection among fishes across short- and long-term time scales 

​As outlined below, I investigate these objectives using an integrative and comparative approach that exploits interspecific variation among fishes in environmental stress tolerance as well as metabolic organization and fuel selection.

1) Mechanisms of Metabolic Energy Balance in Response to Challenging Environments

A large part of my research is focused on the responses of fishes to hypoxia and temperature extremes, two ubiquitous environmental stressors capable of perturbing metabolic energy balance via direct (e.g. impairment of cellular energy supply) or indirect (e.g. ecological) effects.

Hypoxia
A major goal of my research is to explain the physiological bases of the large interspecific variation in hypoxia tolerance among fishes. Specifically, I investigate how fishes modulate energy supply and demand during hypoxia exposure in order to maintain metabolic energy balance as well as achieve metabolic rate depression. Much of my work centers on the heart, a vital yet relatively hypoxia-sensitive organ with a high energy demand. I am investigating how the hearts of hypoxia-tolerant fishes continue to function during oxygen deprivation and how modulation of cardiovascular function integrates with modulation of whole-animal metabolism. These studies have broad relevance because of the increasing incidence of aquatic hypoxia resulting from anthropogenic impacts and because of biomedical interest in evolved strategies of coping with low oxygen.

Temperature
Temperature has pervasive effects on the biology of animals, especially ectotherms. I have been particularly interested in the physiological responses of fishes to seasonally or chronically cold environments. Currently, I am investigating the physiological strategies that temperate and polar fishes have evolved to survive the long, frigid, and food-poor winter. Specifically, I am carrying out projects on the integrated mechanisms of winter dormancy and metabolic rate depression in cunner, a common coastal North Atlantic wrasse fish. Knowledge of seasonal dormancy in fishes has broad implications, such as informing metabolic theories of ecology that depend upon the assumption of predictable effects of temperature on metabolism.

2) Diversity of Metabolic Organization and Fuel Selection Over Multiple Time Scale

A second, complementary stream in my research program is to understand the variation in metabolic organization and fuel selection that exists over acute, acclimatory, and chronic time scales within and among fishes. In particular, I am interested in the phylogenetic patterns of energy metabolism and fuel selection among vertebrates and other animals. I have a major interest in the physiology of chondrichthyan fishes, which include elasmobranchs (sharks and rays) and holocephalans (chimaeras). Among vertebrates, chondrichthyans are metabolically unusual in several ways including showing low to non-existent lipid oxidation in muscle, low levels of fatty acids in blood, chronic utilization of ketone bodies as metabolic fuel, and urea- and methylamine-based osmoregulation. I study the characteristics and interrelationships of these aspects of chondrichthyan physiology in order to better understand the evolution of metabolism in this group and vertebrates as a whole.