THE PHYSIOLOGY OF LIFE-HISTORY TRADE-OFFS - EXPERIMENTAL-ANALYSIS OF A HORMONALLY INDUCED LIFE-HISTORY TRADE-OFF IN GRYLLUS-ASSIMILIS

Adult Gryllus assimilis given an analog of juvenile hormone exhibited reduced flight muscles and enlarged ovaries similar to those found in naturally occurring flightless individuals of species that are polymor phic for dispersal capability. Control and hormone-treated (flightless ) G. assimilis did not differ in the amount of food consumed or assimi lated on any of three diets that differed in nutrient quantity. Thus, enhanced ovarian growth of flightless individuals resulted from increa sed allocation of internal nutrients to reproduction (i.e., a trade-of f) rather than from increased acquisition of nutrients. Compared with flight-capable controls, flightless G. assimilis also had reduced whol e-organism respiration, reduced respiration of flight muscles, and red uced lipid and triglyceride (flight fuel) reserves. These differences are remarkably similar to those between naturally occurring flightless and flight-capable morphs of other Gryllus species. Results collectiv ely suggest that the increased allocation of nutrients to ovarian grow th in flightless G. assimilis and other Gryllus species results from r educed energetic costs of flight muscle maintenance and/or the biosynt hesis or acquisition of lipids. Reduction in these energetic costs app ears to be an important driving force in the evolution of flightlessne ss in insects. Respiratory metabolism associated with flight capabilit y utilizes an increasing proportion of the energy budget of crickets a s the quantity of nutrients in the diet is decreased. This leads to a magnification of greater ovarian growth of flightless versus flight-ca pable individuals on nutrient-poor diets.