The Behavioral Responses of Western Toad (Anaxyrus boreas) Larvae to Simultaneous Stressors Public Deposited

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  • Animals can be naturally exposed simultaneously to multiple stressors. These include habitat changes, contaminants, diseases, invasive species, parasitism, and predation. Exposure to various combinations of biotic and abiotic stressors may induce behavioral changes that affect the way an individual interacts within its environment.Like other groups of organisms, amphibians are exposed to a wide array of both natural and introduced stressors. However, due to their life history and utility in experimental studies, amphibians can serve as useful models to examine how an animal behaves when encountering various stressors. Unlike other vertebrates, amphibians have a biphasic life cycle and are aquatic or terrestrial during different times of their life cycle. In their aquatic phase, amphibians may use chemical cues to detect the presence of stressors. For example, predators may emit chemical cues that an amphibian could detect, or another amphibian that has been captured may emit chemical cues that alert nearby conspecifics of a threat. Moreover, amphibians may use chemical cues to detect parasites when parasites are at certain life stages.In this thesis, I experimentally tested the behavioral reactions of the larvae of a model amphibian species to the presence of alarm cues emitted by amphibian larvae, a pathogen, and a parasite. The pathogen and parasite were an emerging infectious chytrid fungus and a trematode, respectively. Although the interaction between anti-pathogen, anti-parasite and anti-predator responses in larval amphibians has received some attention, results have shown strong interspecific variation in behavioral responses by amphibians to pathogens, parasites, and predators. Moreover, there is less information about the response of amphibians to simultaneous stressors. To examine the behavioral responses of an amphibian to predation cues, pathogens, and parasites I exposed western toad larvae to combinations of the chytrid fungus, Batrachochytrium dendrobatidis (Bd), a trematode parasite, and conspecific alarm cues in a fully factorial experiment. Based on the findings of Han et al. (2011), I predicted that prior exposure to Bd would result in tadpoles having increased activity levels when in the presence of echinostome trematode ocercariae and conspecific alarm cues. Based on the findings of Hews and Blaustein (1985), I also predicted that tadpoles exposed to echinostome cercariae and conspecific alarm cues would avoid the conspecific alarm cues. I found that prior Bd exposure did not influence activity levels of tadpoles exposed to echinostome cercariae and conspecific alarm cues but it did influence avoidance behaviors. Tadpoles that had been previously exposed to Bd displayed increased avoidance behaviors when in the presence of echinostome cercariae and conspecific alarm cues when compared to tadpoles that had only been exposed to echinostome cercariae and conspecific alarm cues. The results fromthis research provide more information about the interactions of commonly co-occurring stressors and an emerging pathogen and their effects on amphibian behavior.
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