Chromosome-level genome assembly of Scathophaga stercoraria provides new insights into the evolutionary adaptations of dung flies

The yellow dung fly Scathophaga stercoraria is a widely distributed species in high-altitude regions of the Northern Hemisphere. It plays important roles as a decomposer, predator, and pollinator in the ecosystem. As a staple model organism, S. stercoraria serves as a standard test species for assessing the toxicity of drug residues in livestock dung and has been the focus of numerous studies. The genetic mechanisms underlying the ecological adaptability of S. stercoraria remain poorly understood. To fill the gap, we first assembled a high-quality chromosome-level genome of S. stercoraria, resulting in a final assembly size of 549.64 Mb, with a contig N50 of 4.06 Mb, and 92.53 % of the sequence anchored to six chromosomes. Gene family analysis revealed an expansion of Toll (Toll1), GNBP3, Cyp303a1, Cyp4d14, Cyp6g1, OR67d, and yolk protein genes in the S. stercoraria genome. Transcriptome analysis indicated that most genes in the trypsin and carboxypeptidase gene families are predominantly expressed during the larval stage, whereas the alpha-Amylase gene family is mainly expressed during the adult stage. Additionally, PGRP-SC is highly expressed during the larval stage, OBPs are primarily expressed during the adult stage, and yolk protein genes exhibit female-biased expression. Our study not only provides a new resource for the dung flies genomic pool, but also identifies the expression patterns of key ecologically adaptative genes and gene families at the developmental stages, which provides new insights into the ecological adaptive evolution of dung flies.