Eating in a losing cause: limited benefit of modified macronutrient consumption following infection in the oriental cockroach Blatta orientalis

Abstract

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.

Testing evolutionary explanations for the lifespan benefit of dietary restriction in fruit flies ( Drosophila melanogaster )

“…However, there are some exceptions to the pattern (Table 1). Other than several methodological differences between studies ( Sieksmeyer et al 2019;Ponton et al 2020;Roberts and Longdon 2020), these differences may be driven by the particular host-pathogen pair, as diet alters various components of the host response and pathogen performance, and these relationships vary between systems (e.g., Lee et al 2006;Povey et al 2009, Povey et al 2014Miller and Cotter 2018;Cotter et al 2019;Wilson et al 2020). Further evidence for host-pathogenspecific effects of diet comes from a meta-analysis of the effect of host nutrition on pathogen virulence, which found both positive or negative effects on virulence depending on the system (Pike et al 2019).…”

“…2019; Sieksmeyer et al. 2019; Ponton et al. 2020; Roberts and Longdon 2020), these differences may be driven by the particular host‐pathogen pair, as diet alters various components of the host response and pathogen performance, and these relationships vary between systems (e.g., Lee et al.…”