Evolutionary genetics of energetic performance

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Evolutionary genetics of energetics | Evolutionary genetics of stress tolerance

Environmental ethanol and acetic acid present a toxic challenge to species that inhabit rotting fruit, but efficient catabolism of these compounds yields a valuable pool of acetyl-CoA to fuel metabolic processes. D. melanogaster has evolved a remarkable ability to tolerate and utilize ethanol and acetic acid, presumably allowing for niche expansion. This project characterizes how ethanol metabolism and membrane physiology interact in the evolution of toxin and temperature tolerance.

A. Modeling physiological performance as a function of biochemical flux. A model of biochemical flux through the three-step ethanol metabolic pathway reveals a ridge of high ethanol tolerance in the phenotypic landscape relating ADH and ACS activities to tolerance. Genotypes with high ADH activity can nonetheless have low tolerance when paired with low ACS activity, presumably due to accumulation of toxic intermediates. This suggests an interesting evolutionary dynamic that we are modeling and empirically testing, where the selective effects of genetic variants that enhance ADH activity depend upon the genetic background and activity of Acs.

B. Interactions between membranes, temperature and toxins. Organisms in nature do not experience single, isolated selection pressures. A remaining challenge is to describe phenotypic evolution as the integrated outcome of multiple selection pressures. Ethanol disrupts membrane function by making membranes more fluid. Because flies are ectotherms, their survival depends upon adjusting membrane fluidity in response to both environmental temperature and ethanol. Membrane fluidity can significantly affect ethanol tolerance. Moreover, a gene regulating membranes, the dSREBP transcription factor, also regulates expression of ethanol metabolism genes! We are combining experimental and lab-evolution manipulation of ethanol, acetic acid and temperature to link expression differences within candidate pathways to toxin and temperature tolerance. Of particular interest are gene/enzymes, such as Pld, that respond to cold acclimation but also affect ethanol tolerance. Investigating gene/enzymes with pleiotropic effects on multiple physiological traits is key to understanding,

1) how multiple functions of a single gene constrain or enhance trait evolution, and
2) how enzymes with conserved function evolve new roles in particular species.