Effects of macronutrient balance on immune-reproductive trade-offs in the tropical house cricket Gryllodes sigillatus

All organisms must allocate finite energy resources to a variety of physiological systems, which often leads to trade-offs between them. The quality of food that is available, particularly the macronutrient composition, impacts energy allocation in complex ways. In insects, the effect of protein and carbohydrate levels have been particularly well studied, with less focus on the effect of excess lipids. In this experiment, we examine the effect of high carbohydrate, high protein, and high lipid diets on mass, egg-laying, immune function, and survivorship in female Gryllodes sigillatus. Our results support past findings, demonstrating that high protein concentration increases female reproductive output. The high lipid diet had similar effects, with significantly more eggs produced than any other treatment group. Two weeks into the experiment, we injected half of the surviving crickets with lipopolysaccharides to initiate an immune challenge, while the other half received a sham injection. Our data suggests that crickets fed on the high lipid or high protein diets made a terminal reproductive investment following the immune challenge. However, the crickets fed the high lipid diet who received a sham injection had low lytic activity and survivorship, suggesting that their investment in reproduction led to trade-offs with immune function and lifespan. This suggests that nutrient imbalances can directly impact an organism's energy allocation, though additional research is needed to understand the mechanisms.