Illness-induced anorexia and its possible function in the caterpillar, Manduca sexta.
Although many animals exhibit illness-induced anorexia when immune-challenged, the adaptive significance of this behavior remains unclear. Injecting Manduca sexta larvae (caterpillars) with live bacteria (Serratia marcescens), heat-killed bacteria or bacterial lipopolysaccharides resulted in a decline in feeding, demonstrating illness-induced anorexia in this species. We used M. sexta to test four commonly suggested adaptive functions for illness-induced anorexia. (1) Food deprivation did not reduce the iron content of the hemolymph. (2) Immune-challenged M. sexta were not more likely to move to a different part of the plant. Therefore, the decline in feeding is unlikely to be an adaptive response allowing the animal to move away from a patch of contaminated food. (3) M. sexta force-fed S. marcescens bacteria were not more susceptible to a S. marcescens systemic infection than were M. sexta force-fed nutrient broth. (4) Force-feeding infected M. sexta during illness-induced anorexia did not increase mortality and short-term food deprivation did not enhance survival. However, force-feeding M. sexta with a high lipid diet (linseed oil and water) resulted in an increase in mortality when challenged with S. marcescens. Force-feeding sucrose or water did not reduce resistance. Force-feeding a high lipid diet into healthy animals did not reduce weight gain, suggesting that it was not toxic. We hypothesize that there is a conflict between lipid metabolism and immune function, although whether this conflict has played a role in the evolution of illness-induced anorexia remains unknown. The adaptive function of illness-induced anorexia requires further study in both vertebrates and invertebrates.
Adamo
Shelley A
SA
Department of Psychology and Neuroscience, Dalhousie University, Halifax, NS, Canada. sadamo@dal.ca
Fidler
Tara L
TL
Forestell
Catherine A
CA
D000222:Adaptation, Physiological; D000818:Animals; D000855:Anorexia / Q000209:etiology* / Q000276:immunology; D001522:Behavior, Animal / Q000502:physiology*; D004195:Disease Models, Animal; D004734:Energy Metabolism; D005247:Feeding Behavior / Q000502:physiology*; D018402:Manduca / Q000276:immunology* / Q000378:metabolism / Q000382:microbiology; D015213:Neuroimmunomodulation / Q000276:immunology / Q000502:physiology; D016868:Serratia Infections / Q000150:complications* / Q000276:immunology; D012706:Serratia marcescens / Q000276:immunology*