Impacts of predator odours and conspecific disturbance cues on minnow thermal tolerance

Warming waters can affect fish community dynamics, potentially exacerbating predator-prey asymmetries in behavioural and physiological metrics of thermal tolerance. Further, differing responses of prey fish species to concurrent predation risk and warming highlight the need to understand these impacts in various contexts, especially with at-risk species. This study explored variation in thermal tolerance between the Threatened pugnose shiner (Miniellus anogenus) and non-threatened congener blackchin shiner (Miniellus heterodon) given concurrent exposure to warming and predation risk via chemical cues. Using a series of three channel-side experiments, we (1) explored whether predator odours from centrarchids affect the thermal tolerance of pugnose shiner and blackchin shiner, (2) explored how conspecific disturbance cues impacted blackchin shiner thermal tolerance and (3) quantified the thermal tolerance of two centrarchid species (largemouth bass (Micropterus nigricans) and pumpkinseed (Lepomis gibbosus)) predators and qualitatively compared this to the two shiner species. We found that blackchin shiner had a lower critical thermal maximum (CT_Max) when given predator odours compared to a water control, demonstrating a plastic upper thermal limit in response to risk. In contrast, the CT_Max of pugnose shiner did not differ between treatments, indicating that they may lack the capacity to respond to these concurrent stressors. The CT_Max of blackchin shiner and pugnose shiner increased over the summer coinciding with increasing water temperature in their home habitat. However, when blackchin shiner received disturbance cue relative to the water control in a separate assay, the effect of seasonal acclimatization on CT_Max was reduced. Finally, largemouth bass qualitatively exhibited a CT_Max that was higher than the shiners, but pumpkinseed did not. Continuing to explore how predator-prey relationships change with warming waters may strengthen our predictive capacity when examining future climate-change scenarios.