The geometry of nutrient-space based life-history trade-offs: sex-specific effects of macronutrient intake on the trade-off between encapsulation ability and reproductive effort in decorated crickets

Life-history theory assumes that traits compete for limited resources resulting in trade-offs. The most commonly manipulated resource in empirical studies is the quantity or quality of diet. Recent studies using the Geometric Framework for nutrition, however, suggest that trade-offs are often regulated by the intake of specific nutrients but a formal approach to identify and quantify the strength of such trade-offs is lacking. We posit that trade-offs occur whenever life-history traits are maximised in different regions of nutrient space, as evidenced by non-overlapping 95% confidence regions of the global maximum for each trait, and large angles (θ) between linear nutritional vectors and Euclidean distances (d) between global maxima. We then examined the effects of protein and carbohydrate intake on the trade-off between reproduction and aspects of immune function in male and female Gryllodes sigillatus. Female encapsulation ability and egg production increased with the intake of both...