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Brownlee, Graham Robert Paul

University of British Columbia

Temperature, due to its influence on biochemical reaction rates, is one of the fundamental drivers of physiology for life on Earth. Because of this relationship, one of the predominant challenges species face in persisting in a changing climate is responding to shifts and perturbations in their thermal environment. While evolutionary processes can favourably shift phenotype distributions in response to altered thermal histories and demographic processes can improve genetic diversity and support population size and growth, possessing rapid-response mechanisms at the organismal level can assist the immediate persistence of a population facing extreme temperatures. Physiological plasticity is a process that can allow species to respond to a changing environment and improve their survival or maintain ecological performance. However, not all species are able to increase their upper thermal tolerance when facing more stressful temperatures, and while higher tolerance limits may improve survival in the short-term, there can be important and underappreciated impacts in sublethal responses like reproductive capacity. The primary goal of my thesis was to test the physiological plasticity of upper thermal tolerance, cardiac thermal tolerance, and reproductive capacity in an important rocky intertidal zone foundation species, Mytilus californianus (Conrad, 1837) following long-term aerial acclimation. Additionally, I tested the seasonal variation in upper thermal tolerance M. californianus expressed during the summer of 2021 and documented the effects of the Pacific Northwest heat dome on mussel survival in wave-exposed and wave-sheltered beds. I found that M. californianus substantially increases its upper thermal tolerance and maximum heart rate following acclimation to increasing aerial temperatures (22°C, 28°C, 34°C), but reproductive capacity is reduced at higher temperatures. M. californianus’ upper thermal tolerance increased over the summer of 2021, but to a lesser degree than the shifts produced at higher acclimation temperatures. Finally, I found minimal mortality in wave-exposed mussel beds following the heat dome, but substantial mortality in wave-sheltered beds. While plasticity in the upper thermal tolerance of M. californianus can improve persistence following short-term warming and heatwaves, declining reproductive capacity may have important population-level consequences on longer timescales that require further investigation to better understand the costs and benefits of physiological plasticity.

Text

2022-05-16

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/81578

Zoology

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/