Triploidy drives vector capacity and expansion of the parthenogenetic tick Haemaphysalis longicornis.

The Haemaphysalis longicornis tick, an important arthropod vector native to East Asia, has expanded its range to Oceania and the American continents, where populations are exclusively parthenogenetic females. While the parthenogenetic population possesses a stable triploid genetic system, the absence of a triploid genome assembly has prohibited us from understanding their genetic evolution and biological traits. Here, we present a chromosome-level, haplotype-resolved triploid genome assembly of the parthenogenetic population by integrating ultra-deep long-read high-fidelity, short-read high-throughput chromosome conformation capture, and isoform sequencing technologies. The phylogenetic analysis suggested that triploid genome originated from an autopolyploid event rather than interspecific hybridization. We identified functional genes that enable parthenogenetic ticks to complete embryogenesis without fertilization. Parthenogenetic ticks showed higher tolerance to Rickettsia and virus infections, with more differential expressed genes compared to bisexual ticks. They exhibited lower levels of deleterious mutations across the genome and a broader global distribution predicted by ecological niche modeling.