High rate of movement of one (mdg3) out of four transposable elements in a natural population of Drosophila melanogaster.

We have analysed by in situ hybridization the insertion site polymorphism of the copia, mdg1, mdg3, and P transposable elements in diploid genomes of wild males from a natural population of Drosophila melanogaster. The values of observed average degree of individual heterozygosity for all elements except mdg3 deviate statistically from the values expected by site frequencies, revealing a tendency toward homozygosity as if drift or a structuration in the population was operating. The high degree of heterozygosity for mdg3 which in addition does not deviate from the expected value, suggests that recent high rate of movements has strongly countered the population host effect on this element. Hence, heterozygosity for TEs may well reflect the history of the population, and reveals temporary high rate of site movement existing in natural populations.