Critical Role of Insertion Preference for Invasion Trajectory of Transposons

Abstract

Transposable elements (TEs) are mobile DNA sequences that have been highly successful at invading eukaryotic genomes. It is unclear how TE families reach high copy number given the expectation that some novel insertions will be deleterious. It has been hypothesized that TE families may evolve to target and insert into specific DNA sequences to adjust the underlying distribution of fitness effects for new insertions. Preferentially inserting into neutral sites could minimize the cumulative deleterious load of a TE family, allowing the mean TE copy number to increase with less risk for host population extinction. To test this hypothesis, we constructed simulations to explore how the transposition probability and insertion preference of a TE family influence the evolution of mean TE copy number and host population size, allowing for extinction. We find that extinction is most common in our simulations under high transposition probabilities, but, as we reduce transposition rates, the risk of extinction persists while the preference for neutral insertion sites is high. In the absence of mechanisms that regulate TE transposition, a preference for neutral insertion sites is not protective and, in fact, actively accelerates both an increase in TE copy number and the time to population extinction.