Response to Chemical Alarm Cues under Weakly Acidic Conditions: A Graded Loss of Antipredator Behaviour in Juvenile Rainbow Trout

• Published in: Water, air, and soil pollution air, and soil pollution, 2008-03, Vol.189 (1-4), p.179-187
• Main Authors: Leduc, Antoine O.H.C, Lamaze, Fabien C, McGraw, Lindsay, Brown, Grant E
• Format: Article
• Language: English
• Subjects: Acidification; Acidity; Acids; Alarm behavior; Alarm pheromone; Animal, plant and microbial ecology; Anthropogenic factors; Anti-predator behavior; Applied ecology; Aquatic organisms; Atmospheric Protection/Air Quality Control/Air Pollution; Biological and medical sciences; Brackish; Chemical contaminants; Chemical stimuli; Chemoreception; chemoreceptors; Climate Change/Climate Change Impacts; Conspecifics; Distilled water; Drinking water; Earth and Environmental Science; Ecotoxicology, biological effects of pollution; Environment; Environmental monitoring; Experiments; Fish; Fishing; Freshwater; Freshwater fish; Fundamental and applied biological sciences. Psychology; General aspects; Hydrogeology; Juveniles; Laboratories; laboratory animals; Lethal effects; Marine; Oncorhynchus mykiss; pH effects; physiological response; Predation; Prey; Risk assessment; Salmonidae; sensory disorders; Soil Science & Conservation; Studies; Trout; water pollution; Water Quality/Water Pollution; Wildlife; Within-subjects design
• ISSN: 0049-6979; 1573-2932
• DOI: 10.1007/s11270-007-9566-y

A wide variety of aquatic organisms, including juvenile salmonids, assess local predation risks using chemosensory cues. Such chemical cues are typically released from injured conspecifics and their detection may lead to species-typical antipredator behaviour, increasing the probability of prey to survive during predator encounters. Studies have demonstrated however, that under weak acidification (pH ~6.0), the response towards these chemical alarm cues is impaired. However, it remains unknown if the loss of response is graded (i.e., the behavioural response decreases with a reduction in pH) or if there is a threshold pH at which prey can no longer detect the alarm cues. We conducted two laboratory experiments to examine the effects of a graded reduction in pH on the behavioural response of juvenile rainbow trout to conspecific chemical alarm cues. The results of our first experiment suggest that at pH 6.6 and above, the alarm cues elicited a strong antipredator response, while alarm cues buffered to pH 6.2 did not (i.e. not different from distilled water). However, alarm cues buffered to pH 6.4 elicited a weak response, suggesting a graded response. We directly tested this in our second experiment using a repeated measures design. The response to alarm cues at varying pH levels did indeed follow a graded loss of function. Together, our results suggest that juvenile rainbow trout exhibit a reduction in the response to conspecific alarm cues proportional to ambient acidity and that the response to these critically important cues is lost at pH below 6.4. As the detection and response to these chemical alarm cues have been shown to confer direct survival benefit to individuals, these results are therefore presented in relation to possible sub-lethal effects of anthropogenic acidification to freshwater fish.