The metabolic basis of life history variation: genetic and phenotypic differences in lipid reserves among life history morphs of the wing-polymorphiccricket, Gryllus firmus

The flight-capable morph of the wing-polymorphic cricket, Gryllus firmus, a ccumulated a substantially greater quantity of total lipid and triglyceride , compared with the obligately flightless morph, during the first five days of adulthood. Increased lipid accumulation in the flight-capable morph was genetically based, and was produced when ovarian growth is substantially r educed in that morph. Temporal changes in lipid levels suggest that the hig her triglyceride reserves in the flight-capable morph fed a high-nutrient d iet were produced by elevated lipid biosynthesis. By contrast, on a low-nut rient or high carbohydrate diet, increased lipid levels in the flight-capab le morph appeared to result primarily from decreased lipid utilization. Inc reased biosynthesis or retention of triglyceride (the major flight fuel in Gryllus) by the flight-capable morph may significantly divert nutrients fro m egg production and hence may be an important physiological cause of its r educed ovarian growth. The obligately flightless morph allocated a greater proportion of total lipid to phospholipid than did the flight-capable morph . No functionally-significant differences in total lipid or triglyceride we re produced between morphs during the last nymphal stadium. A second flight less morph, derived from the flight-capable morph by histolysis of flight m uscles during adulthood, also had reduced amounts of total lipid and trigly ceride but increased ovarian growth compared with the flight capable morph on the standard (high-nutrient) diet. Important qualitative and quantitativ e aspects of lipid metabolism differ genetically between the flight-capable and flightless morphs of G. firmus and likely contribute importantly to th eir respective adaptations for flight capability vs. reproduction. This is the first study to document genetically-based differences in energy reserve s between morphs of a complex (phase, caste, flight) polymorphism in which morphs also differ genetically in key life history traits. (C) 2001 Elsevie r Science Ltd. All rights reserved.