Morphological traits and mitogenome of Thaumapsylla breviceps orientalis endemic to China provide insight into the evolution of the order Siphonaptera

The Thaumapsylla breviceps orientalis is endemic to China and exhibits extreme host specificity (monoxenous). This study reports the first mitogenome sequenced for the family Ischnopsyllidae and provides comprehensive analysis of both the morphological characteristics and mitogenome of T. b. orientalis. The assembled mitogenome is 15,631 bp in length with a high AT content (78.5%), and its codon usage bias is predominantly shaped by natural selection. Evolutionary analysis based on evolutionary rates and nucleotide diversity across different families within Siphonaptera revealed that Pulicidae has the fastest evolutionary rate and the highest nucleotide diversity, a pattern likely driven by differences in their hosts and habitats. We observed that early-diverging flea lineages are predominantly polyxenous, whereas later-diverging lineages are primarily pleioxenous or monoxenous. Phylogenetic results indicate that the taxonomic status of the families Ctenophthalmidae, Vermipsyllidae, and Hystrichopsyllidae requires further study and revision. This research addresses a key knowledge gap in Ischnopsyllidae mitogenomics and clarifies the phylogenetic relationships within the order Siphonaptera.