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Eating in a losing cause: anorexia and macronutrient manipulation by a cockroach fails to boost immunity

By Thorben Sieksmeyer, Shulin He, Benno Kuropka, Christoph Weise, Paul R Johnston, Alejandro Rodríguez-Rojas, Dino P. McMahon

Posted 05 Jun 2019
bioRxiv DOI: 10.1101/652826

Host-pathogen interactions can lead to dramatic changes in host feeding behaviour. One aspect of this includes self-medication, where infected individuals consume substances such as toxins, minerals or secondary compounds or alter their macronutrient consumption to enhance immune competence. Another aspect includes illness-induced anorexia, which is a general mechanism adopted by animals following infection. Anorexia is thought to assist host immunity directly or by limiting the nutritional resources available to pathogens. Here, we recorded macronutrient preferences of the global pest cockroach, Blatta orientalis to investigate how shifts in host macronutrient dietary preference and quantity interact with immunity following sublethal bacterial infection. We compared the survival of uninfected and infected individuals on diets enriched with carbohydrate (C) or protein (P) and conducted food-choice experiments after challenging hosts with the common entomopathogenic soil bacterium Pseudomonas entomophila. We then carried out a quantitative proteomic analysis and an antimicrobial activity assay of hemolymph from infected individuals that had been restricted to diets with defined macronutrient compositions. We find that diets enriched for P reduce cockroach survival. However, following immune challenge by P. entomophila, cockroaches significantly reduced their overall nutrient intake, particularly of carbohydrates, and increased the ratio of protein (P:C) consumed. Surprisingly, these behavioural shifts did not significantly improve cockroach immunity or survival, with negligible differences in immune protein abundance and antimicrobial activity between infected individuals placed on P- or C- rich diets.

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