Fitness-related physiological traits play key roles in both the adaptive responses of organisms to environmental change, and the formation of reproductive barriers between locally adapted populations. Therefore, identifying the mechanistic basis for variation in these traits is a critical aspect of understanding local adaptation and early-stage reproductive isolation. My research addresses this need by integrating comparative physiology, genetics and genomics to provide novel insights into the mechanisms that underlie intraspecific variation in tolerance limits, metabolic rate and oxidative phosphorylation. In this talk, I demonstrate these approaches using my graduate work on adaptive responses to anthropogenic climate change in the Atlantic killifish (Fundulus heteroclitus), and my postdoctoral work on hybrid breakdown, mitochondrial performance and mitonuclear compatibility in Californian tiger copepods (Tigriopus californicus). Taken together, these studies reveal the immense complexity and polygenic nature of the physiological and genetic mechanisms that underlie population divergence and local adaptation, and illustrate the power of my integrative approach for studying the evolution of physiological systems. My research not only highlights the pivotal role that physiological traits play in adaptive processes, but also addresses a fundamental goal of modern biology: mechanistically linking genotype to phenotype.

Human use of synthetic chemical compounds, such as pharmaceuticals and personal care products, is on the rise in developed countries. Many of these chemicals are discharged into freshwater ecosystems via, for example, municipal wastewater effluents. While the concentrations in surface waters are often unlikely to cause direct mortality, there is rising concern about how chronic exposure to sub-lethal amounts of these pollutants may directly or indirectly affect animal fitness. I will discuss a series of experiments I conducted addressing how pharmaceuticals and municipal wastewater effluents impact wild fish across scales of biological organization, from physiology to behaviour to changes in fish community composition. I will compare my results from controlled laboratory studies with findings from in situ field exposures and from studies using animal tracking technologies. Our current understanding of how chemical contaminants affect aquatic organisms is largely based on individual-level responses. Yet, understanding and mitigating the impacts of anthropogenic pollution requires knowledge of how pollutants affect animals in their natural social environment and habitats. I will therefore highlight how my research program is closing these knowledge gaps by focusing on complex inter- and intra-specific interactions (e.g., predator-prey, social dominance) in realistic environments.

Ecological and evolutionary success of animals depends on the expression of phenotypes that are compatible with their environment. In order to understand how specific physiological phenotypes arise, and the degree of plasticity or flexibility of these phenotypes, it is critical that we integrate the study of physiology across different levels of biological organisation. In my research, I have used ionoregulatory systems (salt and water balance) of freshwater fishes as a model to demonstrate how the genome and environment interact to influence phenotypes and how these interactions change over life history to shape physiological systems. In particular, I have studied how fishes sustain Na+ absorption, a process critical to maintaining internal ion and water balance, over development and in response to a range of environmental conditions (ionic strength, pH, contaminant exposure). In this presentation, I will discuss the molecular mechanisms of Na+ absorption by rainbow trout, how they change over development, and the implications that this has in understanding how fish at different stages of life history respond to changes in environmental conditions. I will also discuss the use of CRISPR/Cas9 gene editing as a tool to knock out genes that regulate Na+ absorption in zebrafish and explore how the resulting reduction in genetic complexity influences the expression and plasticity of phenotypes. This research highlights the importance of integrating molecular, organismal, and environmental physiology to understand how fishes occupy different environmental niches and how they respond to environmental change.