Nutrient regulation strategies differ between cricket morphs that trade-off dispersal and reproduction

Nutrient regulation should covary with life history, but actual demonstrations of this connection are rare. Here, we use a wing-polymorphic cricket, Gryllus firmus, that trades off dispersal and reproduction; the long-winged morph with functional flight muscles [LW(f)] is adapted for dispersal at the expense of egg production, while the short-winged (SW) morph is adapted for egg production at the expense of flight. We explore the extent to which these two morphs differentially regulate macronutrient intake to best match their life-history strategy. In a choice' experiment, we offered female crickets of each morph [LW(f) and SW] two nutritionally complementary foods varying in protein and digestible carbohydrate content. In a second no-choice' experiment, we confined crickets to one of five foods, each with a different protein/carbohydrate ratio. In both experiments, and for both morphs, we measured food intake, mass gain and lipid concentration. In the choice' experiments, LW(f) females selected a more carbohydrate-biased diet than SW females. The two morphs gained similar total mass, but the LW morph had higher lipid concentration. In the no-choice experiment, the two morphs practised different nutrient consumption rules'. SW females ate similar total nutrient amounts (protein plus carbohydrate) across diets, while LW(f) females decreased intake as the protein/carbohydrate ratio of the available food became increasingly imbalanced. Overall mass gain was marginally higher in the SW morph and lowest for both morphs on the diets that were extremely carbohydrate biased. LW(f) and SW females had similar lipid concentrations across the diets, even though LW(f) crickets ate less carbohydrate on the two carbohydrate-biased diets. Our data suggest that for LW(f) females, there are costs of overeating nutrients in excess of requirements, but they are efficient at utilizing ingested nutrients. Our results shed new light on how the nutritional environment interacts with the direct trade-off between dispersal and reproduction occurring in adult G.firmus crickets. Dispersal is linked to heightened diet selectivity and an emphasis on nutrients promoting flight fuel (lipid) storage over protein acquisition for egg laying, such that nutritional regulation complements the metabolic mechanisms that generate this trade-off. Lay Summary