The effects of chemical alarm cues on fish physiology and development
Predator-prey interactions are such an important part of ecosystem function and structure.Predation exerts pressure on prey species who must adapt and respond to predators in orderto survive and reproduce. Many aquatic prey species have developed a mechanism ofdetecting prey through the use of chemical alarm cues which alert conspecifics during a predation event. Recently, there has been a growing body of researchthat shows the importance of non-consumptive effects of predation via CACs. Studies haveshown that exposure to CACs can induce dramatic behavioural and morphological responses.Few studies, however, have looked at the physiological responses to predation risk which mayhave fitness consequences just as important as behavioural or morphological responses. Thisstudy aims to investigate effects of CACs on the physiology and development of fish duringearly life stages. The larval stage generally has the highest mortality rates for most fish specieswhich is why it is important to understand how non-consumptive effects of predationinfluence these life stages. Furthermore, as anthropogenic stressors become more prominentthroughout natural ecosystems, it is important to understand how these affect preyresponses to predation threat. Chapter 2 looks into the effects of embryonic predation risk by investigating whether thereare changes in the fitness and the anti-predator behaviour of embryonic and larval mottledtriplefin (Forsterygion capito) following chronic, embryonic exposure to CACs. Thisexperiment contains 2 parts; 1) exposing triplefin embryos to chronic predation risk via pulsedconspecific CAC’s and measuring changes in yolk sac utilisation and embryonic heart rate asa proxy for metabolism; 2) measuring post-hatch morphometric attributes in the larvae, suchas size of yolk sac, standard length and weight. Results showed that embryonic CAC exposureinduced significantly higher heart rates at 16 and 37 days post-fertilisation when comparedto a saltwater control. The increased metabolism, associated with elevated heart rates,resulted in accelerated yolk sac utilization during the embryonic phase and therefore smalleryolk sacs at 37 dpf. Larval yolk size and standard length and activity rate was measured at <1days post hatch (dph). Results showed that there was no effect of treatment on larvalstandard length or activity rate but yolk size was significantly smaller in larvae exposed toCACs. Predation is a major influence on prey behaviour and morphology, and understandinghow embryonic and larval development is influenced by predation stress provides insight onwhat drives these adaptation. Chapter 3 examines the morphological and physiological responses of the Ambon damselfish(Pomacentrus amboinensis) to the combined exposure of CACs and microplastics, highlightingany interactive effects between the two stressors. Settlement stage juveniles of the Ambondamselfish (Pomacentrus amboinensis) were exposed to conspecific alarm cues and/orpolystyrene microplastics over a 2.5-week period to observe the effects on morphology andthe oxidative stress response. Antioxidant enzymes vital to the oxidative stress response suchas catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPOX)andglutathione-S-transferase (GST) were measured as well as markers of oxidative damage,including protein carbonyls and lipid peroxidation. Morphological parameters such asstandard length and body depth were also be measured to identify any developmental effectscaused by predator threat and microplastic ingestion. Results showed that fish exposed toCAC and fish exposed to microplastics generated a strong oxidative stress response with anincrease in levels of antioxidant enzymes, protein carbonyls and lipid peroxides. Fish exposedto combined CACs and microplastics showed an additive response whereby oxidative stresslevels were higher compared to fish exposed to either CACs or microplastics alone. No effectwas found on morphology but fish exposed to CACs did have a smaller mean body depth thancontrols. This is some of the first to highlight the physiological stress response to predationrisk and how microplastic pollution can compound this response. This study demonstrates the physiological and developmental effects of predation risk onearly life stage fish and discusses the potential fitness consequences when combined withan anthropogenic stressor.
Advisor: Allan, Bridie; Burrit, David; Johnson, Sheri
Degree Name: Master of Science
Degree Discipline: Marine Science
Publisher: University of Otago
Keywords: New Zealand; Triplefin; Embryo; Microplastic; Chemical alarm cues; Stress response; embryonic development; Pomacentrus amboinensis; Forsterygion capito; great barrier reef; embryonic response; predation threat; physiology; anti-predator behaviour; neophobia; oxidative stress response; antioxidant enzymes
Research Type: Thesis