Positive association betweencopiatransposition rate and copy number inDrosophila melanogaster

Rates of copia transposition were determined directly, by cytological in situ hybridization analysis of sites of copia insertion in progeny of males from sublines of an inbred strain with different genomic copia copy numbers. Copia transposition rate was positively and nonlinearly associated with copia copy number. This relation cannot be simply explained by mutations in a single host factor that normally suppresses transposition, or by mutations in copia elements themselves. We postulate that the number of copia virus-like particles, necessary for copia transposition, could depend nonlinearly on copia copy number. Deleterious side-effects of the transposition process may be an important force controlling copia copy number in natural populations.