Food or fear: hunger modifies responses to injured conspecifics in tadpoles
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Animals must balance the conflicting needs to forage and avoid predation. The optimal balance of risk and reward should depend on the individual’s state, particularly hunger status. Satiated individuals are hypothesized to react more strongly to risk than hungry individuals, for which the necessity for food overrides perceived danger. We tested this in wood frog (Lithobates sylvaticus) tadpoles by comparing the response of fasted and fed tadpoles to injured conspecifics (alarm cue) and uninjured conspecifics (control). Food restriction significantly affected the activity levels of tadpoles and the impact of injured conspecific cues on activity. Fed tadpoles responded little to these cues, tending to decrease activity. Hungry tadpoles were more active overall and responded to injured conspecific cues by increasing activity. We propose that hungry tadpoles increase their activity in response to an injured conspecific because, in addition to indicating danger, this cue represents a nutrient source for this opportunistically cannibalistic species, and hungry tadpoles should thus adopt risky behavior to acquire this valuable resource. Differences in hunger may therefore explain variation among studies of tadpole responses to injured conspecifics. Future studies in aquatic organisms should consider the role of hunger status when assessing antipredator behavior.
KeywordsAlarm cues Antipredator behavior Cannibalism Hunger Predation risk State-dependent behavior
We thank B. Chitterlings and several anonymous reviewers for feedback that greatly improved this manuscript. We thank T. Maret, A. Stoler, and J. Vreeland for assistance locating field sites for collections and R. Rosier and S. Smiles for help preparing the study site. This work was partially supported by an Animal Behavior Society student research award to BEC. All aspects of this work comply with current laws in Pennsylvania and USA. Animals were collected under permit #488 from the Pennsylvania Fish and Boat Commission, with appropriate site-specific permission granted by the PA Department of Conservation and Natural Resources and the PA Game Commission. Procedures were approved by the Pennsylvania State University Institutional Animal Care and Use Committee (IACUC protocol #33469).
- Carlson B. E. & T. Langkilde, 2014. Predation risk in tadpole populations shapes behavioural responses of prey but not strength of trait-mediated indirect interactions. Oikos (in press).Google Scholar
- Fraker, M. E., F. Hu, V. Cuddapah, S. A. McCollum, R. A. Relyea, J. Hempel & R. J. Denver, 2009. Characterization of an alarm pheromone secreted by amphibian tadpoles that induces behavioral inhibition and suppression of the neuroendocrine stress axis. Hormones and Behavior 55: 520–529.PubMedCrossRefGoogle Scholar
- Gillette, R., R.-C. Huang, N. Hatcher & L. L. Moroz, 2000. Cost-benefit analysis potential in feeding behavior of a predatory snail by integration of hunger, taste, and pain. Proceedings of the National Academy of Sciences of the United States of America 97: 3585–3590.PubMedCentralPubMedCrossRefGoogle Scholar
- Hagman, M., 2008. Behavioral responses by tadpoles of six Australian species to chemical cues from other tadpoles. Herpetological Conservation and Biology 3: 239–246.Google Scholar
- Kats, L. B. & L. M. Dill, 1998. The scent of death: chemosensory assessment of predation risk by prey animals. Ecoscience 5: 361–394.Google Scholar
- Leary, S., W. Underwood, R. Anthony, S. Cartner, D. Corey, T. Grandin, C. B. Greenacre, S. Gwaltney-Bran, M. A. McCrackin, R. Meyer, D. Miller, J. Shearer & R. Yanong, 2013. AVMA Guidelines for the Euthanasia of Animals: 2013 Edition. American Veterinary Medical Association. Available at: https://www.avma.org/kb/policies/documents/euthanasia.pdf.
- Petranka, J. W., 1989. Response of toad tadpoles to conflicting chemical stimuli: predator avoidance versus “optimal” foraging. Herpetologica 45: 283–292.Google Scholar
- R Development Core Team, 2012. R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing, Vienna.Google Scholar