Intralocus sexual conflict over optimal nutrient intake and the evolution of sex differences in lifespan and reproduction

Despite widespread variation in lifespan across species, three clear patterns exist: sex differences in lifespan are ubiquitous, lifespan is commonly traded against reproduction, and nutrition has a major influence on these traits and how they trade-off. One process that potentially unites these patterns is Intralocus Sexual Conflict (IASC) over the optimal intake of nutrients for lifespan and reproduction. If nutrient intake has sex-specific effects on lifespan and reproduction and nutrient choice is genetically linked across the sexes, IASC will occur and may prevent one or both sexes from feeding to their nutritional optima. Here we determine whether this process is operating in the cricket Gryllodes sigillatus. We show that protein and carbohydrate intake have contrasting effects on lifespan and reproduction in the sexes and that there are strong positive intersexual genetic correlations for the intake of these nutrients under dietary choice. This divergence in nutrient effects, combined with the genetic architecture for nutrient choice is predicted to accelerate the evolutionary response of nutrient intake in males but constrain it in females, suggesting they are losing the conflict. Supporting this view, males and females were shown to regulate nutrient intake to a common ratio that was not perfectly optimal for lifespan or reproduction in either sex, especially in females. Our findings show that IASC over the optimal intake of nutrients is likely to be an important process generating sex differences in lifespan and reproduction and may help explain why females age faster and live shorter than males in G. sigillatus.