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The energetic/metabolic basis of life history trade-offs. The energetic basis of life history trade-offs has been a central topic in evolutionary biology for over six decades. However, this aspect of life history evolution is still poorly understood [see Zera and Harshman (2001) for review]. For the past 10 years we have been using wing polymorphism as a model to investigate this topic. The most general finding derived from a variety of studies is that flight-capable females must allocate a significant proportion of their energy budget to maintenance metabolism of the large flight muscles, and accumulation of large quantities of lipid flight fuels. This, in turn, reduces nutrients available for egg production and is the energetic cause of the reduced fecundity of flight-capable vs. flightless females. These studies are the first to directly identify energetic costs of flight capability, a subject of speculation for many decades, and are the most detailed investigations to date of the energetic causes of a life history trade-off.
Ongoing research is breaking new ground by investigating the metabolic causes of the increased lipid accumulation in the flight-capable morph (NSF-funded, 10/98-9/03). Experiments involve radiotracer studies of metabolism and characterizations of enzymes of lipid biosynthesis and catabolism. The main goal is to identify the specific aspects of intermediary metabolism that have been modified during adaptive evolution, leading to morphs that are genetically-programmed to primarily biosynthesize yolk protein for eggs versus lipid for flight fuels. We also plan to identify the specific mechanisms by which hormones control the flow of nutrients into egg yolk vs. lipid biosynthesis in alternate wing morphs. These studies are resulting in the first detailed synthesis of evolutionary genetics, metabolic biochemistry, and endocrinology.