Integrative and Comparative Biology Advance Access published online on June 22, 2009
Integrative and Comparative Biology, doi:10.1093/icb/icp046
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Exploitation of secondary metabolites by animals: A response to homeostatic challenges
*Department of Biological Sciences, Boise State University, Boise, ID 83725, USA; Strathclyde Innovations in Drug Research (SIDR) and Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow G4 0NR, UK; Primate Research Institute, Kyoto University, Inuyama, Aichi 484, Japan; Department of Wildland Resources, Utah State University, Logan, UT 84322-5230, USA; ¶Department of Anthropology, California State University, Sacramento, CA 95819, USA; ||Department of Pharmaceutical and Biological Chemistry, University of London, Centre for Pharmacognosy and Phytotherapy, London WC1N 1AX, UK
Correspondence: 1E-mail: jenniferforbey{at}boisestate.edu
We propose that the exploitation of the bioactive properties of secondary metabolites (SMs) by animals can provide a "treatment" against various challenges that perturb homeostasis in animals. The unified theoretical framework for the exploitation of SMs by animals is based on a synthesis of research from a wide range of fields and although it is focused on providing generalized predictions for herbivores that exploit SMs of plants, predictions can be applied to understand the exploitation of SMs by many animals. In this review, we argue that the probability of SM exploitation is determined by the relative difference between the cost of a homeostatic challenge and the toxicity of the SM and we provide various predictions that can be made when considering behavior under a homeostatic perspective. The notion that animals experience and respond to costly challenges by exploiting therapeutic SMs provides a relatively novel perspective to explain foraging behavior in herbivores, specifically, and behavior of animals in general. We provide evidence that animals can exploit the biological activity of SMs to mitigate the costs of infection by parasites, enhance reproduction, moderate thermoregulation, avoid predation, and increase alertness. We stress that a better understanding of animal behavior requires that ecologists look beyond their biases that SMs elicit punishment and consider a broader view of avoidance or selection of SMs relative to the homeostatic state. Finally, we explain how understanding exploitation of SMs by animals could be applied to advance practices of animal management and lead to discovery of new drugs.