Oral Presentation Society for Molecular Biology and Evolution Conference 2016

Rapid establishment of a piRNA based defense system – evidence from the P-element invasion dynamics in experimentally evolving D. simulans populations (#224)

Robert Kofler 1 , Viola Nolte 1 , Kirsten-Andre Senti 1 , Christian Schloetterer 1
  1. VetMedUni Wien, Wien, --- SELECT A STATE ---, Austria

The P-element, one of the best understood eukaryotic transposable elements (TEs) recently invaded natural D. simulans  populations. We captured a natural D. simulans population from Florida at an early stage of the invasion and set up a replicated experimental evolution study in hot and cold environments. This opens the unprecedented opportunity to study a natural invasion of a TE with the aid of high throughput sequencing technologies in replicated populations evolving in different environments.We show that in all replicate populations of a given environment the P-element rapidly spreads with a remarkable consistency.  In the hot environment P-element copy numbers increased 16-fold up to generation 20 and attained a stable copy number of about 30 per haploid genome. No further increase could be noted during the next 40 generations of experimental evolution. By contrast, at cold conditions the speed of the invasion is much slower, the P-element multiplied 4-fold by generation 30. Interestingly, the P-element invasion only results in a modest reactivation of resident TE families in D. simulans.The leveling out of the P-element invasion at hot conditions could be due to i) a balance between transposition events and negative selection against TE insertions ii) non-autonomous truncated copies of the P-element, which have been shown to down-regulate transposition activity and iii) piRNAs. RNA-seq and small RNA-seq analysis argues that the dominant factor containing the spread of the P-element is the emergence of piRNAs complementary to the P-element.