P elements and the determinants of hybrid dysgenesis have different dynamics of propagation in Drosophila melanogaster populations.

Intraspecific hybrid dysgenesis (HD) appears after some strains of D. melanogaster are crossed. The predominant idea is that the movement of transposable P elements causes HD. It is believed that P elements appeared in the D. melanogaster genome in the middle of the last century by horizontal transfer, simultaneously with the appearance of HD determinants. A subsequent simultaneous expansion of HD determinants and P elements occurred. We analyzed the current distribution of HD determinants in natural populations of D. melanogaster and found no evidence of their further spread. However, full-sized P elements were identified in the genomes of all analyzed natural D. melanogaster strains independent of their cytotypes. Thus, the expansion of P elements does not correlate with the expansion of HD determinants. We found that the ovaries of dysgenic females did not contain germ cells despite the equal number of primordial germ cells in early stages in dysgenic and non-dysgenic embryos. We propose that HD does not result from DNA damage caused by P element transposition, but it would be the disruption in the regulation of dysgenic ovarian formation that causes the dysgenic phenotypes.