Population genetic structure of G asterophilus pecorum in the K alamaili N ature R eserve, X injiang, based on mitochondrial cytochrome oxidase ( COI ) gene sequence

Gasterophilosis is a significant threat to equids in the desert steppe of X injiang, C hina, where G asterophilus pecorum ( F abricius) ( D iptera: G asterophilidae) is the dominant botfly species. A population analysis was conducted on 195 individual G . pecorum larvae from three host species, P rzewalski's horse, the domestic horse and the A siatic wild ass. The distribution of haplotypes of the maternally inherited mitochondrial cytochrome oxidase subunit I ( COI ) gene was analysed to assess the population differentiation of G . pecorum . High haplotype diversity was observed among G . pecorum populations from all host species, indicating that the G . pecorum infecting one host had multiple maternal ancestors. A phylogenetic tree showed six clades, suggesting a high degree of genetic differentiation. A constructed haplotype network described both the origin of the haplotypes and the population structure. The findings indicated that G . pecorum infections within P rzewalski's horses were mainly transmitted from A siatic wild asses. Clade 1 was found to be the most primitive group and to have evolved to be highly adaptable to the desert steppe. Clade 2 originated from C lade 1, potentially as a result of the annual migration of domestic horses. Revealing the differentiation of the G . pecorum population is important for elucidating the aetiology of G asterophilus infection in X injiang and for planning appropriate control measures.