Abstract
BackgroundMany theoretical models predicting the dynamics of transposable elements (TEs) in genomes, populations, and species have already been proposed. However, most of them only focus on populations of sexual diploid individuals, and TE dynamics in populations partly composed by autogamous individuals remains poorly investigated. To estimate the impact of selfing on TE dynamics, the short- and long-term evolution of TEs was simulated in outcrossing populations with various proportions of selfing individuals.ResultsSelfing has a deep impact on TE dynamics: the higher the selfing rate, the lower the probability of invasion. Already known non-equilibrium dynamics (complete loss, domestication, cyclical invasion of TEs) can all be described whatever the mating system. However, their pattern and their respective frequencies greatly depend on the selfing rate. For instance, in cyclical dynamics resulting from interactions between autonomous and non-autonomous copies, cycles are faster when the selfing rate increases. Interestingly, an abrupt change in the mating system from sexuality to complete asexuality leads to the loss of all the elements over a few hundred generations. In general, for intermediate selfing rates, the transposition activity remains maintained.ConclusionsOur theoretical results evidence that a clear and systematic contrast in TE content according to the mating system is expected, with a smooth transition for intermediate selfing rates. Several parameters impact the TE copy number, and all dynamics described in allogamous populations can be also observed in partly autogamous species. This study thus provides new insights to understand the complex signal from empirical comparison of closely related species with different mating systems.
Highlights
Many theoretical models predicting the dynamics of transposable elements (TEs) in genomes, populations, and species have already been proposed
TE dynamics from the first generation after introduction to their long-term evolution were explored by individual-based simulations
The selective impact si of each TE insertion can vary from highly deleterious to advantageous according to the distribution probability of selective impacts
Summary
TE dynamics from the first generation after introduction to their long-term evolution were explored by individual-based simulations. The invasion of a TE family is a stochastic process and is partly driven by genetic drift, but contrary to the well-known influence of population size on the fixation probability of deleterious mutations, the invasion frequency of TEs is virtually insensitive to the number of individuals. As the probability of adaptive insertions increases, advantageous elements can be fixed more often (Figure 2B), provided that their positive effect is strong enough to overcome genetic drift These beneficial insertions do not need to maintain their transposition activity to survive, and they eventually become inactive. Genetic drift affects TE sequences, and increases the chances to lose all active copies in the population when the average copy number is low This observation confirms previous findings [22], and highlights a mechanism acting in a direction opposite to the improved purging efficiency in large population-size species [35,36].
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