Asexual reproduction drives the reduction of transposable element load

Theory predicts that sexual reproduction can both facilitate and restrain transposable element (TE) accumulation by providing TEs with a means of spreading to all individuals in a population and facilitating TE load reduction via purifying selection. By quantifying genomic TE loads over time in experimental sexual and asexual Saccharomyces cerevisiae populations, we provide direct evidence that asexual reproduction drives a reduction of TE loads. We show, using simulations, that this reduction occurs via evolution of TE activity, most likely via increased excision rates. Thus, sex is a major driver of genomic TE loads and at the root of the success of TEs.