Genetic diversity and haplotype distribution of Dermacentor reticulatus ticks across Europe, including new data from the Baltic States region

<i>Dermacentor reticulatus</i> is a widely distributed tick species in Europe, whose rapid range expansion and importance as a vector of multiple pathogens have increased scientific interest in its genetic diversity and population structure. The Baltic States region, which has been experiencing <i>D. reticulatus</i> tick migration into northern areas over the last two decades, with its unique ecological and climatic conditions, could offer valuable insights into tick distribution patterns and their genetic structure in northern European ranges. This study aimed to investigate the genetic variation of <i>D. reticulatus</i> across its European range, including new data from the Baltic States. Genetic variability of 83 <i>D. reticulatus</i> tick samples from 42 locations across the Baltic states, central, western, and southeastern Europe was assessed using mitochondrial (12S rRNA, 16S rRNA) and nuclear (ITS2) markers. The study revealed low genetic variability in <i>D. reticulatus</i> populations across Europe, characterized by a dominant haplotype present in the Baltic states as well as central and western Europe. Unique haplotypes discovered in the Baltic region may be associated with environmental factors and the recent range expansion of the species. The presence of unique haplotypes and genetic variability among northern <i>D. reticulatus</i> populations suggests ongoing local adaptation driven by environmental pressures, including regional climate and landscape heterogeneity in newly colonized habitats.