Transposable element landscape in Drosophila populations selected for longevity

Transposable elements (TEs) inflict numerous negative effects on health
and fitness as they replicate by integrating into new regions of the host
genome. Even though organisms employ powerful mechanisms to demobilize
TEs, transposons gradually lose repression during aging. The rising TE
activity causes genomic instability and was implicated in age-dependent
neurodegenerative diseases, inflammation and the determination of
lifespan. It is therefore conceivable that long-lived individuals have
improved TE silencing mechanisms resulting in reduced TE expression
relative to their shorter-lived counterparts and fewer genomic insertions.
Here, we test this hypothesis by performing the first genome-wide analysis
of TE insertions and expression in populations of Drosophila melanogaster
selected for longevity through late-life reproduction for 50-170
generations from four independent studies. Contrary to our expectation, TE
families were generally more abundant in long-lived populations compared
to non-selected controls. Although simulations showed that this was not
expected under neutrality, we found little evidence for selection driving
TE abundance differences. Additional RNA-seq analysis revealed a tendency
for reducing TE expression in selected populations, which might be more
important for lifespan than regulating genomic insertions. We further find
limited evidence of parallel selection on genes related to TE regulation
and transposition. However, telomeric TEs were genomically and
transcriptionally more abundant in long-lived flies, suggesting improved
telomere maintenance as a promising TE-mediated mechanism for prolonging
lifespan. Our results provide a novel viewpoint indicating that
reproduction at old age increases the opportunity of TEs to be passed on
to the next generation with little impact on longevity.