Increased mutation in crosses between geographically separated strains of Drosophila melanogaster.

Mutator activity associated with the common male recombination (MR) chromosomes in Drosophila melanogaster appears to be suppressed in natural populations. Crosses between geographically separated populations, however, lead to the release of mutator activity as measured by a significant increase in visible mutations. Such an increase in mutation in hybrid individuals may be a powerful factor in inducing or releasing variation in nature, and in more extreme instances may contribute to the separation of microdifferentiated populations.