Changes in gene expression and physiology following heat stress in migratory fishes

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University of New Brunswick


As ectothermic animals, the effects of temperature are evident across nearly all levels of fish biology, from behaviour through to gene expression. Wide-ranging, migratory fishes are generally well adapted to changing environmental temperatures, yet the mechanisms underlying this tolerance to change may vary among or even within species. The Striped Bass (Morone saxatilis), which are the focus of recreational and commercial fisheries, is one such wide-ranging fish species that has a wide temperature tolerance. However, the underlying mechanisms are poorly described. Sturgeons are another group of migratory fishes, with economic importance and a wide temperature range, that also represent an ancient fish lineage and with an interestingly muted cortisol stress response, which is uncommon in fishes. The objective of my thesis was to delineate the physiological and transcriptomic responses of these migratory, non-model fish species to temperature increase. The first chapter assessed the physiological changes in Striped Bass exposed to both chronic and acute temperature increases. This study revealed that Striped Bass have an impressive ability to withstand high temperatures (both acutely and chronically), with little change in hematology. Building from the first chapter, I then characterize changes in gene expression in Striped Bass muscle tissue after temperature change. These transcriptomic analyses suggest that a diverse suite of heat shock proteins (HSPs) likely play a major role in the Striped Bass’ tolerance to warm waters, following both acute and chronic exposure. In the last data chapter, I explore both the physiological and gene expression changes in the muscle tissues of two Sturgeon species (Shortnose and Atlantic Sturgeon; Acipenser brevirostrum and A. oxyrinchus, respectively) after acute temperature change. I found that the two Sturgeon species have a markedly different response to acute temperature change; Atlantic Sturgeon undergo many transcriptomic changes with little cortisol increase and Shortnose Sturgeon do the opposite (higher cortisol; few changes in gene expression). Together, these data highlight the variable nature of how fishes cope with changing temperatures (e.g., marked HSP response in Striped Bass vs. nearly none in Sturgeon) and broaden our understanding of the processes underpinning the response to an important environmental variable.