Transposable Elements (TEs) are fragments of selfish DNA that multiply and propagate throughout the genome. These transposition events can lead to DNA damage, which severely impacts the germ-line integrity of the host, and the fitness of their offspring. While the evolution of resistance via the suppression of TE replication has been well characterised, it has been suggested that tolerance— where germ-line fitness is maintained regardless of transposition—could also potentially evolve in the aftermath of a new TE invasion.
The P-element, which first appeared in Drosophila melanogaster mid-way through the 20th century, is one of the best characterised eukaryotic TEs. As D. melanogaster had already been long established as a model organism by the time the P-element incursion occured, this particular host/TE system provides us with an excellent opportunity to study potential variation in TE tolerance both pre- and post invasion. Previous quantitative trait locus (QTL) analysis utilizing variation in natural strains lead to the identification of 22 SNPs associated with greater P-element tolerance in bruno, a gene thought suppresses P-element induced ovarian atrophy. As founder strains were all established in research labs prior to the P-element invasion, this suggests that the observed variation in tolerance is due to standing variation.
In order to develop a historical picture of TE tolerance over time, we performed whole genome sequencing of a panel of D. melanogaster lines collected from different points across the 20th century. We are using these data to determine what alleles were segregating at both the bruno locus and number of genes involved in double-strand break (DSB) repair prior to the invasion of the P-element, and how these allele frequencies changed in the aftermath. In addition to characterising TE tolerance, these historical genomes also give us the opportunity to track and compare other variants that have changed in frequency over the same time period due to other selection pressures, such as climate change and insecticide resistance.