Physiological Responses to Predators and Their Consequences for the Growth/Predation Risk trade-off

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Many organisms respond to the threat of predators by altering their physiology, behavior and morphology. These attempts to reduce their likelihood of being killed by a predator, often come at the cost of reducing growth. Although organisms from bacteria to plants and animals show such responses, the underlying reasons for this trade-off are poorly understood. Reduced growth in the presence of predators may result in part from behavioral responses to reduce feeding, but physiological changes also may play a major role. This research will explore the differences among species and genera of larval damselflies (Hexapoda: Odonata) in physiological response to predators, the consequences of these differences for metabolic resource allocation and behavior, and the evolution of these traits. Five studies will be performed to examine the physiological responses of species and the allocation of ingested resources to various molecules in the body. The first study will survey 12 species to measure natural growth rates and the amount of glucose, glycogen, triglycerides and protein in the organism's body. The second will experimentally determine alterations in growth and allocation to these molecules under treatments of predator presence and food availability in the lab. The third is a field experiment to test whether the results obtained in the controlled laboratory experiment are substantiated in real lakes. The fourth tests hypotheses about the proximate differences between the genera that induce the physiological response. Finally, the fifth examines the broader evolutionary history of this physiological response to predators.This work explores the physiological mechanisms underlying a fundamental difference in ecological performance between two groups of insects. This is critical to understanding how an individual's phenotype shapes its ability to engage in interactions with its environment and with other species. Also, examining how this physiology has evolved provides valuable insights into how species adapt to various environments and to natural and anthropogenically-induced environmental change (e.g., natural habitat shifts, climate change, habitat degradation).