Indirect Costs of Parasitism are Shaped by Variation in the Type of Immune Challenge and Food Availability
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Parasites can inflict indirect fitness costs to their hosts by eliciting costly immune responses. These costs depend on the type and amount of immunostimulants presented to the host immune system but also on the amount of resources available to fuel host immune responses. Here, we investigated how the relative costs of two different types of immune challenge are modulated by variation in food availability. We injected nestling tawny owls (Strix aluco) with either 10 μg of phytohaemagglutinin (PHA) or 20 μg of lipopolysaccharide (LPS), and subsequently raised them under two different food regimes (food-restricted vs. ad libitum). After controlling for food consumption, we found that LPS-injected nestlings lost more body mass than PHA-injected ones only when food-restricted. We also found that body mass gain of owlets fed ad libitum decreased with the intensity of the skin swelling response against LPS, but not PHA. These experimental and correlative results suggest that nestling tawny owls suffered greater immune costs when treated with LPS than PHA, and that variation in the costs of two different types of immune challenge can be exacerbated under conditions of low food availability. Our study highlights the importance of taking into consideration the interplay between host immunity and nutrition in the study of indirect costs of parasitism.
KeywordsCondition-dependent Food availability Immunocompetence Immunopathology Tawny owl
This study was supported by the Swiss National Science Foundation (grant no. PPOOA-102913 and 31003A-120517 to AR, PPOOA-109009 to PB and PBLAP3-124279 to RP) and the Roche Research Foundation (grant no. Mkl/stm 14-2008 to RP). The experiment was approved by the veterinary services of Canton de Vaud (licence no. 1508) and birds were ringed under the legal authorization of the Swiss Agency for the Environment, Forests and Landscape.
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