Host-transposable element coexistence: a matter of resistance, tolerance and trade-off.

Transposable elements (TEs) are ubiquitous, mobile DNA elements that often exist as multiple copies within host genomes. To persist despite ongoing mutational decay, these genomic parasites must continuously generate new insertions into the germline genome, a process that risks compromising host reproductive capacity by disrupting coding regions and regulatory sequences and by reshaping chromosomal architecture. Accordingly, hosts have evolved mechanisms to repress TE activity and reduce its fitness costs. In principle, however, such antagonism could lead to lineage-specific TE extinction, which may be suboptimal for hosts, as TEs possess aspects that confer beneficial functions to them. Therefore, hosts not only resist but also tolerate and even exploit the presence of TEs. In parallel, TEs themselves have acquired and deployed unique strategies that promote their own persistence while limiting harm to the host. This review explores how "peaceful" coexistence between hosts and TEs is achieved, focusing on resistance, tolerance, and the associated trade-offs from both host and TE perspectives.