Rapid increase in genome size as a consequence of transposable element hyperactivity in wood-white (leptidea) butterflies

Characterizing and quantifying genome size variation among organisms and understanding if genome size evolves as a consequence of adaptive or stochastic processes have been long-standing goals in evolutionary biology. Here, we investigate genomesize variation and associationwith transposable elements (TEs) across lepidopteran lineages using a novel genome assembly of the commonwood-white (Leptidea sinapis) and population re-sequencing data fromboth L. sinapis and the closely related L. reali and L. juvernica togetherwith 12 previously available lepidopteran genome assemblies.Aphylogenetic analysis confirms established relationships among species, but identifies previously unknown intraspecific structure within Leptidea lineages. The genome assembly of L. sinapis is one of the largest of any lepidopteran taxon so far (643Mb) and genome size is correlatedwith abundance of TEs, both inLepidoptera in general andwithin Leptideawhere L. juvernica fromKazakhstanhas considerably larger genomesize than any other Leptidea population. Specific TE subclasses have been active in different Lepidoptera lineages with a pronounced expansion of predominantly LINEs, DNA elements, and unclassified TEs in the Leptidea lineage after the split from other Pieridae. The rate of genome expansion in Leptidea in general has been in the range of four Mb/Million year (My), with an increase in a particular L. juvernica population to 72Mb/My. The considerable differences in accumulation rates of specific TE classes in different lineages indicate that TE activity plays a major role in genome size evolution in butterflies and moths.