Work

Population genetics of active transposable elements: overdispersion arises naturally from transposition-deletion-selection balance

Year: 2026

Type: article

Abstract: Active transposable element (TE) families often show overdispersion (variance greater than the mean), which is in contrast to the predictions of classical Poisson-based models and related theories built on the same approximation. To address this gap, we develop a diploid stochastic model of TE dynamics under free recombination, based on a biparental Moran model with transposition, excision, purifying selection, and derive mean and variance dynamics of TE copy numbers at two stages of the life cycle: before and after transposition and excision. We show that overdispersion arises naturally through transposition generating positive linkage disequilibrium between TE insertion sites with the disequilibrium persisting even under free recombination. The higher the transposition rate, the stronger the resulting overdispersion. Underdispersion and Poisson-like variation are instead stage-dependent: neither is expected after transposition and excision, while both remain possible beforehand, governed by the curvature of the fitness function. We further show that maintaining positive equilibrium copy numbers, and thus sustaining overdispersion, requires the net transposition rate to remain below roughly 0.5 insertions per copy per generation, a constraint satisfied by observed natural populations to maintain genome stability. A qualitative comparison with the DPGP3 Zambian Drosophila melanogaster dataset, focusing on TE insertions in high-recombination euchromatic regions shows that most TE families are overdispersed and that many also exhibit the predicted right-skewness and excess-kurtosis patterns, which are predicted by our model. These results identify overdispersion as a natural outcome of active TE dynamics and provide a mechanistic framework for understanding the full distribution of TE copy numbers in highly recombining regions. Statement of significance This study addresses a mismatch between population genetic theory and empirical data on transposable elements (TEs). A detailed analysis of the stochastic model underlying the classical population genetics theory of TEs provides new predictions on the mean and variance of TE copy numbers that accurately match simulation results, and provide an explanation for the right-skewed, heavy-tailed distributions seen in real data. Importantly, we show that the pronounced variability in TE copy numbers, i.e. overdispersion, observed in natural populations emerges naturally from ongoing TE dynamics, even in highly recombining genomic regions. How much overdispersion is predicted further depends on the stage of the life cycle at which copy numbers are counted, before or after transposition and excision.

Source: Genome Biology and Evolution

DOI: 10.1093/gbe/evag244

Authors: Adekanmi Daniel Omole, Peter Czuppon

Institutions: University of Münster, Institute for Biodiversity, Aix-Marseille Université

Language: English

Topic: Chromosomal and Genetic Variations

Subfield: Plant Science

Field: Agricultural and Biological Sciences

Domain: Life Sciences

Open Access status: gold

Estimated APC paid: $2,850

Funder: Deutsche Forschungsgemeinschaft