The role of environmental temperature in immunocompetence and disease susceptibility in bivalves
Disease outbreaks and mass mortality events affecting marine species and ecosystems during periods of high temperature have increased in frequency and intensity over the past several decades. Accordingly, understanding the causes of such thermally-induced outbreaks is increasingly important, particu...
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| Other Authors: | , |
| Format: | Master Thesis |
| Language: | English |
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University of Plymouth
2021
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| Online Access: | http://hdl.handle.net/10026.1/18091 https://doi.org/10.24382/640 |
| Summary: | Disease outbreaks and mass mortality events affecting marine species and ecosystems during periods of high temperature have increased in frequency and intensity over the past several decades. Accordingly, understanding the causes of such thermally-induced outbreaks is increasingly important, particularly in the context of global climate change and predictions of increased pathogen prevalence and disease incidence. Whilst our understanding of immune functions and their adequate energetic provisioning for disease resistance is well developed, little is known on how temperature affects immunological and energetic status in bivalves. Furthermore, even less is known on the potential combined effects between thermal and pathogenic stressors that may further alter host-pathogen dynamics. Consequently, the aim of this thesis was to investigate the individual effects of thermal stress as well as its combined effects with pathogenic challenge on the immunological and energetic condition of bivalves. A rise in temperature from 18 to 21°C caused a significant loss of haemocyte viability (p = < 0.001) in the Pacific oyster, Crassostrea gigas from an average of 80 % to 70 %. Oysters at 21 °C also had a significantly decreased ATP level (p = < 0.001) that fell from an average of 0.78 to 0.51 (µmol g-1). The loss of this immune parameter may indicate stress-induced immunosuppression at higher temperatures, driven by the depletion of this vital cellular biochemical reserve. Exposure of C. gigas to the previously unstudied oyster pathogen, Nocardia crassostreae caused a significant rise in haemocyte counts from an average of 0.623 of to 0.863 (cells 1x106) compared to non-exposed groups. This was associated with a significant loss of glycogen reserves in oysters kept at both 18 and 21 °C, where levels declined from an average of 232 to 105 (µmol g-1) in challenged individuals. Exposure also caused a significant rise in glucose levels (p = 0.002) from an average of 0.34 to 1.42 (µmol g-1) and the total adenylate nucleotides ... |
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