Complete Mitochondrial Genome of Melophagus ovinus from Qinghai-Tibet Plateau Provides Evidence for D-Loop Length Polymorphism

Background/Objectives: Melophagus ovinus is an economically important ectoparasite of small ruminants with a broad global distribution. Although mitochondrial genomes are widely used in population genetic studies, the D-loop region of M. ovinus remains poorly characterized because its high AT content and repetitive structure complicate amplification, assembly, and sequencing. Methods: We sequenced the mitochondrial genome of M. ovinus collected from Qinghai using an integrative approach combining Illumina paired-end sequencing, targeted PCR amplification, and Nanopore long-read sequencing. Comparative genomic analysis was performed against published mitogenomes from Gansu (MH024396) and Xinjiang (NC_037368). Results: The Qinghai mitochondrial genome contained the typical 37 mitochondrial genes within a 14,728 bp conserved region. Comparative analysis revealed exceptionally high conservation (>99.6% sequence identity) among Qinghai, Gansu, and Xinjiang isolates outside the D-loop region. Notably, the D-loop exhibited length polymorphism, with different assembly strategies or samples yielding lengths ranging from 317 bp to 2385 bp. Targeted long-read sequencing of ten individuals identified a predominant D-loop variant of approximately 844 bp in nine samples and a markedly shorter variant of approximately 164 bp in one sample. The short variant was characterized by extensive deletions and a novel 45 bp insertion. Support for this variant was obtained from independent Illumina DNA-seq, RNA-seq, Nanopore sequencing, and de novo assembly analyses. Conclusions: This study provides preliminary evidence for D-loop structural heterogeneity in M. ovinus, suggesting remarkable length polymorphism and complex indel patterns that require further validation. These findings significantly expand the genomic resources available for this important veterinary parasite and establish a foundation for future population genetic and evolutionary studies.