The Genome of the American Dog Tick (Dermacentor variabilis)

Abstract

The American dog tick (Dermacentor variabilis) is a vector of zoonotic pathogens in North America that poses emerging threats to public health. Despite its medical importance, genomic resources for D. variabilis remain scarce. Leveraging long-read nanopore sequencing, we generated a high-quality genome assembly for D. variabilis with a final size of 2.15 Gb, an N50 of 445 kb, and a BUSCO completeness score of 95.2%. Comparative BUSCO analyses revealed fewer duplicate genes in our assembly than in other Dermacentor genomes, indicating improved haplotype resolution. The mitochondrial genome, assembled as a single circular contig, clustered monophyletically with D. variabilis isolates from the Upper Midwest, corroborating regional phylogenetic relationships. Repetitive element analysis identified 61% of the genome as repetitive, dominated by LINEs and LTR elements, with 24% remaining unclassified, underscoring the need for further exploration of transposable elements in tick genomes. Gene annotation predicted 21,722 putative genes, achieving a protein BUSCO completeness of 80.88%. Additionally, genome-wide methylation analysis revealed 9.9% global 5mC methylation, providing the first insights into epigenetic modifications in D. variabilis. Further, nanopore sequencing detected Rickettsia montanensis and a non-pathogenic Francisella-like endosymbiont. These findings expand our understanding of tick genomics and epigenetics, offering valuable resources for comparative studies and evolutionary analyses.