Draft Genome Assembly of Parnassius epaphus Provides New Insights into Transposable Elements That Drive Genome Expansion in Alpine Parnassius butterflies

The expansion of genomes is a major evolutionary force, yet its role in facilitating adaptation to extreme environments remains enigmatic. Here, we investigate alpine Parnassius butterflies, a rare genus characterized by exceptionally large genomes, to unravel the interplay between genome architecture and high-altitude colonization. We present a new, 1.46 Gb draft genome assembly for Parnassius epaphus and perform a comparative analysis across six species. Our findings reveal a massive 3- to 5-fold genome expansion driven predominantly by Long Interspersed Nuclear Elements (LINEs). Counterintuitively, we discover that larger genomes possess a proportionally smaller fraction of young, active transposable elements (TEs), challenging the prevailing paradigm that recent TE proliferation is the primary driver of genome size. Instead, our temporal analysis demonstrates that this expansion is a legacy of two ancient TE waves (~8 and ~14 Mya), which remarkably coincide with major uplift phases of the Tibetan Plateau. We propose a model where the selective retention of these ancient TEs, mechanistically linked to major geological upheavals, provided the crucial genomic plasticity for colonizing Earth’s most extreme terrestrial habitats. This study re-frames TEs not merely as genomic parasites but as pivotal architects of adaptive genome evolution in response to profound environmental change.