# Arms races between selfish genetic elements and their host defence in termites

## TL;DR

This study shows an evolutionary arms race between selfish genetic elements and DNA methylation in termites, similar to host-parasite dynamics.

## Contribution

The study provides strong evidence for co-evolution between transposable elements and DNA methylation in termites.

## Key findings

- Transposable element methylation reduces their success and spread.
- Older transposable elements are less harmful and less active.
- DNA methylation defense is strongest against young transposable elements.

## Abstract

Arms races between parasites and hosts are key drivers of evolution. Selfishly replicating transposable elements (TEs) are thought to follow similar dynamics, but strong evidence is missing. We test this in termites, social insects in which TEs have been linked to ageing. Sequencing genomes and profiling DNA methylation across the termite phylogeny reveal corresponding phylogenetic signals in TEs and TE methylation, indicative of co-evolution. TE methylation reduces TE success, as both TE abundance and spreading efficiency decrease with increasing methylation. TEs also become less harmful with TE age: evolutionarily older TEs spread less, insert less into exons, and erode into short remnants. Correspondingly, defence through methylation is strongest against young TEs. Yet, as in typical host–parasite arms races, some TEs persist, implying resistance or recurrent invasions. Our results reveal arms races between TEs and DNA methylation, positioning TEs as drivers of genome evolution similar to symbionts in organismic evolution.

Termite reproductives are long-lived and their genomes have abundant selfish genetic elements. Using long-read sequencing to profile transposable elements and DNA methylation, Qiu et al. uncover evolutionary arms races between TEs and host defences.