Document: JAM-3-49-3

Induced versus constitutive ethanol tolerance in larvae of Drosophila melanogaster .

FRY, J.D.* ¹ and M.GRIGGS ²

University of Rochester, Rochester NY, 14627, U.S.A. ¹
Utah State University, Logan UT U.S.A. ²

Abstract:
Ethanol can reach toxic levels in breeding sites of wild Drosophila melanogaster, and there is widespread genetic variation for ethanol tolerance within and among populations. An hypothesis for the maintenance of this variation is that ethanol-tolerant genotypes are selected against in the absence of ethanol. To investigate this possibility, we compared two populations selected for ethanol tolerance (E populations) with two control populations (S populations) in survival and development rate in the presence and absence of ethanol. Because ethanol tolerance in larvae can be induced by exposing eggs to ethanol, eggs were pretreated by soaking for 15 hours in solutions either containing (18%) or lacking ethanol. On ethanol food, egg-to-adult survival and development rate of eggs not pretreated with ethanol were higher in the E populations than in the S populations. Pretreating eggs with ethanol dramatically increased the survival of eggs from all populations on ethanol food, with the magnitude of this induction response being greatest in the E populations. On standard food, survival and development rate of eggs not treated with ethanol did not differ among the populations, giving no evidence that adaptation to ethanol resulted in lower fitness in its absence. However, the mechanisms responsible for ethanol tolerance are not fully activated unless eggs are exposed to ethanol, suggesting that ethanol-tolerant genotypes may largely avoid the potential fitness costs of expressing those mechanisms when they are not needed.

Keywords: adaptation, genetic variation, selection

This abstract is being presented at: 10:15 AM in session:
Oral Session #26: Invertebrate Herbivore - Plant Interactions.