Genome assembly for the Sierra Nevada Parnassian (Parnassius behrii) and a brief review of butterfly genome sizes.

The Sierra Nevada Parnassian (Parnassius behrii W.H. Edwards, 1870) (Lepidoptera: Papilionidae) is a high-elevation specialist butterfly endemic to the Sierra Nevada, California. We present a genome assembly for P. behrii, representing the first major genomic resource for the species and greater Parnassius phoebus species complex. The assembly consists of two haplotypes, 1.59 Gb and 1.46 Gb in length, with contig N50 values of 10.93 Mb and 11.84 Mb, scaffold N50 values of 52.56 Mb and 51.90 Mb, scaffold L50 values of 13 and 14, and BUSCO completeness scores of 98.7% and 94.4%, respectively. Both haplotypes are highly contiguous, with 31 chromosome-length scaffolds, including putative Z and W sex chromosomes. We annotated the genome with National Center for Biotechnology Information's (NCBI's) EGAPx pipeline, integrating database and novel transcript alignment with Hidden Markov Model-based gene predictions, yielding 17,191 genes with a BUSCO score of 98.1%. RepeatMasker identified that 26.68% (424.97 Mb) of the genome consists of repetitive elements. We also assembled a mitochondrial genome for P. behrii (15,391 bp) containing 2 rRNAs, 22 unique transfer RNAs, and 13 protein-coding genes. We finally reviewed 514 high-quality butterfly genomes available from the National Center for Biotechnology Information (NCBI). Parnassius species were observed to have the largest genomes, with P. behrii being the largest. This assembly provides a foundational resource for whole-genome research on P. behrii and the broader P. phoebus complex, enabling analyses of evolutionary differentiation, local adaptation, inbreeding, gene flow, taxonomy and conservation practices.