Evolution of immune function in response to dietary macronutrients in male and female decorated crickets

Although dietary macronutrients are known to regulate insect immunity, few studies have examined their evolutionary effects. Here, we evaluate this relationship in the cricket Gryllodes sigillatus by maintaining replicate populations on four diets differing in protein (P) to carbohydrate (C) ratio (P‐ or C‐biased) and nutritional content (low‐ or high‐nutrition) for >37 generations. We split each population into two; one maintained on their evolution diet and the other switched to their ancestral diet. We also maintained populations exclusively on the ancestral diet (baseline). After three generations, we measured three immune parameters in males and females from each population. Immunity was higher on P‐biased than C‐biased diets and on low‐ versus high‐nutrition diets, although the latter was most likely driven by compensatory feeding. These patterns persisted in populations switched to their ancestral diet, indicating genetic divergence. Crickets evolving on C‐biased diets had lower immunity than the baseline, whereas their P‐biased counterparts had similar or higher immunity than the baseline, indicating that populations evolved with dietary manipulation. Although females exhibited superior immunity for all assays, the sexes showed similar immune changes across diets. Our work highlights the important role that macronutrient intake plays in the evolution of immunity in the sexes. We use ~40 generations of experimental evolution to show that male and female decorated crickets evolve stronger immunity of protein‐biased diets than carbohydrate‐biased diets. Surprisingly, within each level of macronutrient bias, crickets also evolve stronger immunity on low nutrient than high nutrient diets. This latter finding reflects the evolution of compensatory feeding behaviour in crickets maintained on lower nutrient diets.