Selection for higher fitness in populations of Drosophila pseudoobscura

Four laboratory populations, each consisting of flies homozygous for a wild second chromosome, were maintained in population cages. Three of them were initially characterized by low fecundity of the females; the fourth was a control. After 15 months, in all three populations with low fecundity this character was much improved; two of them, have reached the control level. The changes observed were presumably due to mutation and selection under highly competitive conditions.