Macronutrient regulation of a polymorphic insect differing in morphological, physiological and life history traits

Among insects, differences in morphological, physiological and life history traits may require intake of dietary macronutrients (proteins and carbohydrates) at disparate levels. Active regulation of these resources may be necessary if natural diets are imbalanced in macronutrient content. The polymorphic cricket Gryllus assimilis exists in two morphs – either short-winged or long-winged. Associated with this polymorphism is a trade-off in reproduction – short-winged morphs have increased ovarian mass compared to long-winged morphs. Accompanying these morphological and life history differences, morphs are likely divergent in their regulation and physiological requirements for macronutrients. Here we studied macronutrient regulation in two morphs by providing newly molted adult females with one of two choice treatments, or one of five different no-choice treatments. The diets used differed in their macronutrient profiles. The choice experiments revealed that long-winged morphs, compared to short-winged morphs, self-selected diets richer in carbohydrates, and that the two morphs gained equal mass, but that long-winged morphs converted more of their ingested carbohydrates to body fat. The no-choice experiments revealed that the two morphs employ different macronutrient regulatory rules, with short-winged morphs being more able to tolerate ingesting nutrients in excess of requirements. The no-choice experiments also suggest that long-winged morphs maintain constant body fat across a range of diets, while short-wing morphs have body fat levels that correlate with diet digestible carbohydrate levels. These results indicate that these two morphs have evolved unique nutrient regulatory responses that are under genetic control and are specifically adapted to suit their particular life-styles.