The Genetic Basis of D. melanogaster-D. simulans Interspecies Difference in Ethanol Resistance
Luna T. Ngo
Mentor: J.J. Emerson
Understanding the genetic basis of adaptation has remained one of the major goals of evolutionary biologists.
Yet, little is known about why a trait that serves as an adaptation in one species does not evolve in its closely
related species. For example, D. melanogaster has the ability to adapt to stressful concentrations of dietary
ethanol, whereas its sibling species D. simulans cannot. Identifying the nature of the genetic changes that are
lacking in D. simulans but allowed D. melanogaster to become resistant to stressful concentration of ethanol is
pertinent to understanding the nature of constraint that prevented evolution of ethanol resistance in D.
simulans. Here I investigated the genetic basis of mel-sim difference in ethanol resistance using interspecies
crosses. In particular, I investigated the effect of Aldehyde dehydrogenase gene, which encodes an enzyme
indispensable for ethanol detoxification in flies, on the mel-sim difference in ethanol resistance. I found that
the hybrids between D. melanogaster and D. simulans are nearly as ethanol resistant as D. melanogaster, suggesting
that genetic changes that increase ethanol resistance in D. melanogaster are dominant over their D. simulans
counterparts. Nonetheless, the difference in Aldh gene of the two species does not account for the difference
in ethanol resistance. Further investigations are being carried out to test the effect of the Alcohol
dehydrogenase enzyme gene, which is also indispensable for ethanol detoxification in D. melanogaster, on the
interspecies difference in ethanol resistance.