Dispersal from the Qinghai-Tibet plateau by a high-altitude butterfly is associated with rapid expansion and reorganization of its genome.

Parnassius glacialis is a typical "Out of the QTP" alpine butterfly that originated on the Qinghai-Tibet Plateau (QTP) and dispersed into relatively low-altitude mountainous. Here we assemble a chromosome-level genome of P. glacialis and resequence 9 populations in order to explore the genome evolution and local adaptation of this species. These results indicated that the rapid accumulation and slow unequal recombination of transposable elements (TEs) contributed to the formation of its large genome. Several ribosomal gene families showed extensive expansion and selective evolution through transposon-mediated processed pseudogenes. Additionally, massive structural variations (SVs) of TEs affected the genetic differentiation of low-altitude populations. These low-altitude populations might have experienced a genetic bottleneck in the past and harbor genes with selective signatures which may be responsible for the potential adaptation to low-altitude environments. These results provide a foundation for understanding genome evolution and local adaptation for "Out of the QTP" of P. glacialis. The butterfly Parnassius glacialis experienced vast environmental transition when it dispersed out of the Qinghai-Tibet plateau. Here, the authors find that P. glacialis has an unusually large genome with rapid accumulation of transposable elements possibly facilitating its evolutionary adaptation. [ABSTRACT FROM AUTHOR]