Paternally inherited P-element copy number affects the magnitude of hybrid dysgenesis in Drosophila simulans and D. melanogaster

Transposable elements (TEs) are repetitive regions of DNA that are able to self-replicate and reinsert themselves throughout host genomes. TEs rapidly propagate throughout populations once introduced, despite the potentially deleterious nature of their spread. Since the discovery of TEs, one of the questions that has been posed is what determines when TEs affect the fitness of their hosts and whether copy number is a cause. P elements (PEs) in Drosophila provide an ideal system through which to study whether the number of PEs, and TEs generally, are an important factor in determining phenotypic defects that within-species F1s suffer. We address this question by inferring the number of PEs in individual isofemale line genomes and measuring whether there is an effect of the P-element copy number on multiple phenotypes associated with the hybrid dysgenesis (HD) syndrome in two species of Drosophila. Consistent with previous reports, we find strong evidence for this effect and a significant increase in fitness defects in F1 females and males as the number of P-element copies in the genome increases. Nonetheless, the effect of the copy number is modulated by temperature and the identity of the species.