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Great Barrier Reef; Analysis of deviance table (Type II tests) for unfed gnathiid survival among temperature treatments and juvenile stages for Cox model. Bolded values are ones mentioned in main text. *** p < 0.001.

Great Barrier Reef; Analysis of deviance table (Type II tests) for unfed gnathiid survival among temperature treatments and juvenile stages for Cox model. Bolded values are ones mentioned in main text. *** p < 0.001.

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Extreme warming events that contribute to mass coral bleaching are occurring with increasing regularity, raising questions about their effect on coral reef ecological interactions. However, the effects of such events on parasite-host interactions are largely ignored. Gnathiid isopods are common, highly mobile, external parasites of coral reef fishe...

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... first trial consisted of 5 temperature treatments, ambient (28 • C), 30 • C, 32 • C, 34 • C and 36 • C. A second trial was also conducted to obtain a finer resolution of the temperature effect, with treatments of 30 • C, 32 • C, 33 • C, 34 • C and 35 • C. Aquaria were individually heated gradually with 100W and 200W aquarium electric heaters (Venusaaqua ® ) over a 10 h period to their desired temperature. Temperature readings were taken daily with an aquarium-mounted digital thermometer (Doutop ® ) to ensure the desired water temperatures were maintained and to calculate the average temperature for each treatment per trial (Table S1a,b). Containers from each treatment were inspected daily for evidence of changes in gnathiid development and mortality. ...
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... test whether survival of gnathiids differed among temperature treatments, we used a proportional hazards Cox mixed-effects model with temperature treatment and gnathiid juvenile stage as categorical fixed effects, aquarium as a random factor, and gnathiid headwidth as a covariate (Table 1 and Table S3). We used ambient temperature (29 • C) and juvenile stage one as the baselines for the analyses. ...
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... S7). The interaction between gnathiid headwidth and juvenile stage was significant (p < 0.0001, Table 1); when further explored separately by stage, the association was largely due to a weakly positive relationship between gnathiid survival and gnathiid headwidth in stage one (p < 0.0001, Table S9a). ...
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... the 87 individuals followed, 60% had molted during the course of the study. Survival differed according to an interaction between temperature and juvenile stage (p = 0.0085, Table 2); when further explored separately by stage (Figure 2), the effect of temperature was significant for stage two (p < 0.0001), and three (p = 0.0009, Figure 2b,c, Table S10b,c), with the strongest effect of temperature being that between the baseline (29 • C) and the 32 • C treatments for stage three (Table S10c, Figure 2c). Survival differed according to an interaction between temperature and headwidth (p = 0.0480, Table 2); when further explored separately by temperature treatment, the effect of headwidth was largely due to non-significant weakly positive relationships between survival and headwidth at 29 • C (p = 0.0758) and 32 • C (p = 0.0718, Table S11a,c). ...
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... differed according to an interaction between temperature and juvenile stage (p = 0.0085, Table 2); when further explored separately by stage (Figure 2), the effect of temperature was significant for stage two (p < 0.0001), and three (p = 0.0009, Figure 2b,c, Table S10b,c), with the strongest effect of temperature being that between the baseline (29 • C) and the 32 • C treatments for stage three (Table S10c, Figure 2c). Survival differed according to an interaction between temperature and headwidth (p = 0.0480, Table 2); when further explored separately by temperature treatment, the effect of headwidth was largely due to non-significant weakly positive relationships between survival and headwidth at 29 • C (p = 0.0758) and 32 • C (p = 0.0718, Table S11a,c). There was a significant effect of temperature on gnathiid survival (p < 0.0001) in Trial 1, driven by lower survival curves for the 36 • C (p < 0.0001) and 32 • C (p = 0.024) treatments, compared with the 28 • C baseline temperature treatment (Table 3 and Table S12, Figure 3). ...
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... differed according to an interaction between temperature and headwidth (p = 0.0480, Table 2); when further explored separately by temperature treatment, the effect of headwidth was largely due to non-significant weakly positive relationships between survival and headwidth at 29 • C (p = 0.0758) and 32 • C (p = 0.0718, Table S11a,c). There was a significant effect of temperature on gnathiid survival (p < 0.0001) in Trial 1, driven by lower survival curves for the 36 • C (p < 0.0001) and 32 • C (p = 0.024) treatments, compared with the 28 • C baseline temperature treatment (Table 3 and Table S12, Figure 3). Overall, the effect of temperature on gnathiid survival was not quite statistically significant (p = 0.0768, Table 3). ...

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... But while it quickly recovered after the first extreme event (possibly due to lower coral cover, see Paula et al., 2021), it did not do so in 2017 and remained low postbleaching (in 2018) (Sikkel et al., 2019). This overall decrease in gnathiids may have been caused by an interaction between the short-term negative impacts of thermal stress on gnathiids, as shown in laboratory studies (Shodipo et al., 2020), and a decline in host availability, causing gnathiid abundance to drop (Sikkel et al., 2019;Triki and Bshary, 2019). Since heatwave intensity and frequency is increasing (Oliver et al., 2018), client fish (e.g., P. amboinensis) population attempts of adaptation to either ocean acidification or parasite infection can quickly be erased following such extreme events, if, for example, individuals that develop tolerance to either parasite infection or OA die during such extreme events. ...
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