Enzymological and radiotracer studies of lipid metabolism in the flight-capable and flightless morphs of the wing-polymorphic cricket, Gryllus firmus

Abstract

The flight-capable morph of the wing-polymorphic cricket, Gryllus firmus, exhibited significantly higher activities of each of five lipogenic enzymes compared with the obligately flightless morph on a standard and a high-carbohydrate diet during early adulthood. Similarly, the rate of incorporation of [ 14 C] -acetate into total lipid was higher in the flight-capable morph during this time. By contrast, activities of lipogenic enzymes and rates of lipid biosynthesis, in general, did not differ between morphs on a low nutrient diet during early adulthood. Differences in lipid biosynthesis account for previously documented differences in lipid reserves between morphs on some, but not all, diets. Results of the present and previous studies indicate that increased lipid biosynthesis in the flight capable morph on standard and high-carbohydrate diets constitutes an important adaptation for flight (production of lipid flight fuel). Lipid biosynthesis is negatively correlated with ovarian growth, and may be an important biochemical component of the trade-off between flight capability and ovarian growth in G. firmus. Morphs also differed in activities of three enzymes of lipid catabolism. However, the extent to which variation in activities of these enzymes between morphs results in variation in lipid catabolism is unclear. Finally, the flight-capable morph had a substantially higher activity of alanine aminotransferase in the fat body. Amino acids may be utilized for lipid biosynthesis or energy production to a greater degree in the dispersing morph compared with the oligately flightless morph. This study is the first to document differences in intermediary metabolism that underlie adaptations of morphs of a dispersal-polymorphic species for flight vs. egg production.