Investigating physiological markers of heat stress in response to water temperature in kākahi (Echyridella menziesii) to provide insight into their vulnerability to anthropogenic climate change : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Physiology, Massey University, Palmerston North, New Zealand
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2022
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Massey University
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Abstract
Anthropogenic climate change (ACC) is expected to increase the water temperatures of aquatic ecosystems, which can cause heat stress in aquatic animals. Kākahi (Echyridella menziesii) are a species of freshwater mussel that are endemic to Aotearoa New Zealand. Kākahi are an ecological and cultural keystone species in Aotearoa New Zealand’s aquatic ecosystems. Little is known about the thermal physiology of this species and, therefore, their vulnerability to increasing water temperatures under ACC. Increasing our knowledge of kākahi thermal physiology and their vulnerability to projected future water temperatures is important for the conservation of the species and the ongoing health of the ecosystems of which they are part. For bivalve species (Class: Bivalvia), measuring the concentrations of heat stress biomarkers in the circulatory fluid is a common method of assessing vulnerability to elevated water temperatures. This has not been attempted in kākahi, leaving a gap in our understanding of how different water temperatures affect their metabolism and physiological performance. In this thesis, I measured the concentrations of three known physiological markers of heat stress (lactate dehydrogenase, alanine aminotransferase, and aspartate aminotransferase) in the haemolymph of kākahi exposed to different water temperatures. This method was used in separate field and laboratory studies to measure potential heat stress at current (2022) summer water temperatures (field) and at projected water temperatures under different warming scenarios (laboratory). In the field study, I found that current summer water temperatures in 2022 did not cause an increase in heat stress biomarker concentrations in kākahi haemolymph. In the lab study, I found no significant increases in heat stress biomarker concentrations in kākahi exposed to 26˚C or 32˚C for seven days. The results suggest that kākahi may be resilient to increasing water temperatures under ACC. Additionally, I extracted DNA from kākahi gill tissue and used primers designed from the consensus sequences of other molluscs to attempt to amplify the heat shock protein 70 (HSP70) gene. This additional piece of research aimed to provide important baseline information to enable future studies to measure changes in HSP70 expression in response to elevated water temperature. The designed primers were unfortunately unsuccessful at targeting the desired gene. However, this work provided important knowledge that will help refine the process for future attempts in identifying the HSP70 gene in kākahi.
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Figures 2, 3, 5, 8 and NIWA Figures are re-used with permission. Figure 6 is ©2010 IEEE and reprinted with permission. Figures 1 and 7 are re-used under a Creative Commons Attribution 4.0 International (CC BY 4.0) license.