Measures of Cortisol, Cytokine Expression and Behavior Change Before and After Pure-Tone Sound Exposure
Cetaceans are exposed to increasing pressure caused by anthropogenic activities in their marine environment. Numerous offshore wind farms are planned or under construction along the west coasts of Taiwan, which will produce high under-water sound pressure levels (SPLs) during pile driving to build offshore wind turbines.1,2 Anthropogenic sound is a potential stressor for marine mammals that may affect health.3 Several studies have interpreted that stress induces a shift in the balance of Th1 and Th2 immune responses in favor of Th2. However, the relationship between stress, hormones, and cytokines secretion is complex and not fully understood. The effects of stress are not uniform and vary with such factors as nature of the stressor, its intensity and duration, and control over the stressor.4 For a better understanding of how anthropogenic impacts affect the physiology of cetaceans, the present study compares levels of cortisol and mRNA expression of cytokines in blood samples and behavior change of bottlenose dolphins (Tursiops truncatus) exposed to different SPLs. Two captive bottlenose dolphins in a pool were exposed to playbacks of 800 Hz pure-tone sound (40 strikes/min, duration 150 ms) for 30 min at three different SPLs (0, 133, 153 dB re 1 µPa). Every test session was conducted beginning at 10:00 am for 3 days, and each SPL was tested in 4–5 sessions, resulting in 12–15 sessions in all. The order (different SPLs) of the sessions was randomized. Blood samples drawn on EDTA (mixed with RNAlater immediately for RNA) and without additive (for cortisol) were obtained before and after sound exposure in 5 min. Six cytokine genes (IL-2Rα, IL-4, IL-10, IL-12, TNF-α, and IFN-γ) were selected for analysis with two verified stable-expressed housekeeping genes (PGK1 and HPRT1) as reference genes by using real-time PCR. The result indicated that cortisol and IL-10 were significantly higher and IFN-γ was significantly lower after high-level sound exposures (153 de re 1 µPa) compared with low-level sound exposures (133 de re 1 µPa) or no-sound controls. However, IL-12 and TNF-α were significantly lower after low-level sound exposures compared with other groups. At high-level, the consequences of a shift toward Th2 immunity, as shown by an increase in IL-10 and decrease in IFN-γ, may be harmful based on the potential susceptibility to viruses or bacteria. At SPL of 133 de re 1 µPa, the dolphins showed more repetitive behavior, and the swimming speed was significantly different at SPL of 153 de re 1 µPa. Further study with real pile-driving sound and including more animals would allow the elucidation of the influence of offshore wind farm construction on dolphins.
This study was funded by the Ministry of Science and Technology, R.O.C. under the contact "The investigation of physiological and ecological effects of offshore wind farm on cetaceans." We thank the staff at the Farglory Ocean Park. We would like to thank all individuals who assisted with the field and laboratory work.
* Presenting author
+ Student presenter
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