Hybrid dysgenesis inDrosophila melanogaster: the evolution of mixedPandMpopulations maintained at high temperature

Abstract

SUMMARY: The ability of hybrid dysgenesisPfactors to survive and multiply under conditions of strong negative sterility selection was studied in mixedPandMlaboratory cultures. Eight populations were initiated with varying proportions ofPandMstrains. Mixed populations and controls were maintained for seventeen generations at 27 °C, a temperature sufficiently high to induce maximum frequencies of sterility in dysgenic hybrids. The two components of dysgenesis,Pfactor activity and cytotype, were monitored every generation for the first ten generations and intermittently thereafter. With one exception, all the mixed populations evolved to thePtype indicating thatPfactors can survive and multiply, despite low initial frequency and strong negative selection against dysgenic hybrids. However, the average level ofPfactor activity attained at equilibrium was considerably lower than that of thePstrain control population maintained under the same conditions. It was also lower than the equilibrium level ofPfactor activity attained in a similar experiment carried out at a lower temperature, suggesting that selection favouredPfactors with weak rather than strong sterility potential.