Globally spreading ticks evolved asexual reproduction multiple times

A new study has revealed that the Asian longhorned tick, Haemaphysalis longicornis, has independently evolved the ability to reproduce asexually, known as parthenogenesis, multiple times throughout its global expansion. This adaptation, according to researchers, likely plays a crucial role in the tick’s rapid spread across continents and its increasing impact as a disease vector. The findings, published in PNAS Nexus in August 2026, challenge previous assumptions about the genetic uniformity of these invasive arthropods. The Asian longhorned tick is a significant public health concern due to its capacity to transmit several serious pathogens, including the SFTS virus, Rickettsia bacteria, and Theileria parasites. Its bites can also trigger allergic reactions in humans, particularly those sensitive to red meat. Initially restricted to parts of East Asia and Russia, the tick has since established itself in Oceania and was first identified in the United States in 2017. Researchers believe that the ability of certain female ticks to reproduce without mating contributes significantly to their proliferation beyond traditional habitats. Ryo Nakao and his team conducted a comprehensive genomic analysis of both native Japanese populations and introduced populations in regions such as Fiji, New Caledonia, and Australia. They employed advanced techniques involving whole mitochondrial genomes and genome-wide single nucleotide polymorphism (SNP) data derived from MIG-seq technology. Their sample set included five laboratory strains, two of which reproduced sexually while the other three relied solely on parthenogenesis. Initial phylogenetic trees based on mitochondrial DNA suggested two main clades corresponding to different reproductive strategies. One clade predominantly consisted of parthenogenetic females, which appeared to have dispersed globally. However, the discovery of three male ticks within this otherwise all-female group complicated the narrative. Additionally, SNP analyses indicated gene flow between the clades, implying that parthenogenesis did not arise once but rather evolved independently on multiple occasions. These results suggest that the evolutionary flexibility of H. longicornis allows it to adapt rapidly to diverse environments. The ability to switch between sexual and asexual reproduction could provide a survival advantage in new territories where finding mates might be difficult. Such plasticity would enable the ticks to colonize new areas more effectively, reinforcing their status as a formidable invasive species. The study also highlights the complexity of tracking invasive species through genetic markers alone. While the initial assumption was that parthenogenetic ticks represented a distinct lineage, the presence of males within that group indicates a more intricate evolutionary history. Furthermore, the observed gene exchange between clades suggests that the boundaries between reproductive strategies are not rigid, allowing for potential hybridization or genetic reassortment. Researchers emphasize that understanding the mechanisms behind the tick’s dispersal is essential for developing effective control measures. Given the tick’s role in transmitting diseases, insights into its reproductive biology could inform targeted interventions aimed at curbing its spread. The study underscores the importance of continued genomic surveillance of invasive species to anticipate future ecological impacts. The implications extend beyond entomology, influencing fields such as epidemiology and conservation biology. As climate change continues to alter ecosystems, the adaptive capacities of organisms like H. longicornis will become increasingly relevant. Monitoring how these traits emerge and persist across different populations will be critical for predicting and mitigating their effects on human and animal health.