Experimentally evolving Drosophila erecta populations may fail to establish an effective piRNA-based host defense against invading P-elements

Length distribution of small RNAs mapping to the P-element during the invasions. Data are shown for naive flies and the three replicates (top panel) at all five generations (right panel). We extracted small RNAs, either from whole bodies of female flies (light gray panels) or from ovaries (dark gray panels). For each sample, we show the percentage of the small RNAs mapping to a given size category (hence the total number of reads adds up to 100% in each sample). Sense RNAs are on the positive y-axis, and antisense RNAs are on the negative y-axis. The total number of siRNAs (20–22 nt) and piRNAs (23–29 nt) mapping to the P-element are shown (antisense piRNAs are in parentheses).