Enzymatic and molecular bases of trade-offs in lipid metabolism that underlie a life history trade-off.

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Enzymatic and molecular bases of trade-offs in lipid metabolism that underlie a life-history trade-off Anthony J. ZeraUniversity of Nebraska The ultimate goal of this project is to identify genetically-based modifications in intermediary metabolism that underlie genetically-based variation in life history traits. Experiments will be undertaken in the wing-polymorphic cricket, Gryllus firmus, which exists as a flight-capable morph that delays egg production and a flightless morph with substantially enhanced egg production. Previous studies demonstrated that egg production in the flight-capable morph is reduced because a large amount of triglyceride flight fuel must accumulate. Previous studies also have documented that the increased accumulation of triglyceride results from increased fatty-acid biosynthesis and increased diversion of fatty acids into the production of triglyceride as opposed to phospholipid. Proposed research will build on this extensive data base and has two goals: The first is to identify the enzymological characteristics and gene-regulatory mechanisms in the flight-capable morph responsible for the increased biosynthesis of fatty acid. The second goal is to identify functional modifications of enzymes at the triglyceride/ phospholipid biosynthetic branch point that result in the preferential diversion (i.e. trade-off) of fatty acid into triglyceride flight fuel in the flight-capable morph. Four key lipid-biosynthetic enzymes will be purified to homogeneity, antibodies will be raised against them, and then used to measure enzyme concentration. This will test the hypothesis that elevated enzyme activity of lipid-biosynthetic enzymes is due to elevated enzyme concentration. Purified enzymes will be characterized kinetically to test the alternate hypothesis that morph-differences in enzyme activities result from changes in catalytic efficiency, due to factors such as differential phosphorylation. Message abundance of genes encoding the four lipogenic enzymes will be compared to determine the extent to which morph-differences in enzyme activity/concentration result from differences in gene expression. Finally, five enzymes controlling flux through the triglyceride/phospholipid biosynthetic branch point will be compared between flight-capable and flightless morphs with respect to a variety of functional characteristics such as specific activity, differential phosphorylation, and binding to membranes. The goal will be to identify differences in the enzymes that are responsible for the morph-specific trade-off in the diversion of fatty acid into triglyceride (flight fuel) vs. phospholipid (key egg component) in flight-capable vs. flightless morphs.This study will contribute significantly to our understanding of the functional causes of life history evolution, a poorly understood topic in evolutionary biology. It will comprise the most detailed analysis of alterations in intermediary metabolism that give rise to life history variation and trade-offs that occur in natural populations. This will be the first study to identify specific enzymatic alterations at a branch point (triglyceride/phospholipid) in intermediary metabolism that underlies a life history trade-off. This project will contribute to the development of a deep integration of life history evolution and evolutionary biochemistry, which was initiated in the previous NSF-funded study. This project will also contribute to the development of human resources by providing integrative training for a postdoctoral associate in evolutionary biology, enzymology, and molecular biology, and will also provide numerous significant undergraduate research opportunities.