Nutrient absorption and utilization by wing and flight muscle morphs of the cricket Gryllus firmus: implications for the trade-off between flight capability and early reproduction

Absorption efficiency (AD, approximate digestibility, assimilation efficien cy) of various macronutrients and conversion of absorbed nutrients to bioma ss (ECD) were compared among the two types of flightless morph and the flig ht-capable morph of the cricket, Gryllus firmus. No biologically significan t phenotypic or genetic difference in AD for carbohydrate, protein or lipid was observed among morphs fed either a high-nutrient (100%) or a low-nutri ent (25%) diet. Thus, previously-documented differences among adult morphs in carbohydrate and lipid content must be caused by processes other than va riation in nutrient absorption by morphs during adulthood. Relative absorpt ion efficiency of total dry mass of food by morphs of G. firmus appears to be a valid indicator of relative AD of total calories. Morphs did not diffe r phenotypically or genetically in the excretion of end products of nitroge n metabolism (uric acid, hypoxanthine plus xanthine) on either the high nut rient or the low nutrient diet. Nutritional indices corrected for excreted nitrogenous metabolites were very similar to uncorrected indices, and the p attern of variation among the morphs was the same for corrected or uncorrec ted values. Each of the two types of flightless morph converted a greater p roportion of absorbed nutrients into body mass, mainly ovaries, and allocat ed a smaller proportion of assimilated nutrients to respiration than did th e flight-capable morph. Moreover, the trade-off between respiration and ear ly reproduction was substantially magnified on the low nutrient diet. These results extend previous findings of a trade-off between flight capability and early reproduction in wing-polymorphic Gryllus species (1) to diets of very different nutrient quantity, and (2) to flightlessness arising from di fferent causes: blockage of flight muscle development in juveniles vs histo lysis of fully-developed flight muscles in adults. (C) 2000 Elsevier Scienc e Ltd. All rights reserved.