HEAT-SHOCK RESISTANCE IN DROSOPHILA POPULATIONS - ANALYSIS OF VARIATION IN RECIPROCAL CROSS PROGENY

Genetic variation for resistance to high temperature stress was studie d in populations of D. melanogaster and D. buzzatii from different geo graphic regions. Drosophila melanogaster individuals were presented wi th either a direct short exposure to a high temperature or exposure to high temperature after receiving a pretreatment, which increased resi stance. Heat-stress resistance varied among populations, with one much more resistant than all others under both treatments. Another possess ed low stress resistance when exposed without the heat pretreatment; b ut with pretreatment, resistance increased relative to the other popul ations. Evidence from reciprocal crosses suggests that the X chromosom e of the more resistant population carries alleles that greatly increa se resistance, and that one or more factors on the autosomes also affe ct resistance. Non-additive interaction effects among the three less r esistant populations, were suggestive that all differ for various elem ents that contribute to stress resistance, and that some clearly chang e inducible resistance more than basal levels. In D. buzzatii, the two least resistant populations were genetically very similar. Crosses to the more resistant population gave results suggesting that the low re sistance to heat is dominant. A small X-chromosome effect that increas ed resistance, and a dominant enhancer of male resistance also may hav e contributed to variation in resistance.