Concerted transpositions of mobile genetic elements coupled with fitness changes in Drosophila melanogaster

In an inbred low-activity (LA) strain of Drosophila melanogaster with a lowlevel of fitness and a complex of inadaptive characters, in situhybridization reveals an invariant pattern of distribution of threecopia-like elements (mdg-1, mdg-3, and copia). Rare, spontaneous, multipletranspositions of mobile elements in the LA strain were shown to be coupledwith a drastic increase of fitness. A changed pattern of various types ofmobile elements was also observed on selecting the LA strain for higherfitness. High-fitness strains show transpositions of mobile elements todefinite chromosomal sites ("hot spots"). Concerted changes in the locationof three different mobile elements were found to be coupled with anincrease of fitness. The mdg-1 distribution patterns were also examined intwo low-fitness strains independently selected from the high-fitness ones.Fitness decrease was accompanied by mdg-1 excision from the hot spots oftheir location usually detected in the high-fitness strains. The resultssuggest the existence of a system of adaptive transpositions of mobileelements that takes part in fitness control.