Population genetic structure and demographic history of Dermacentor marginatus Sulzer, 1776 in Anatolia

Dermacentor marginatus is a medically important tick species due to its preference humans and domestic animals as hosts and its vectorial competence, yet it remains understudied in many regions. This study aimed to examine the population structure and demographic history of D. marginatus using the cox1 and ITS2 genes, focusing on populations from Central and Northeast Anatolia-two regions on either side of the Anatolian Diagonal, a natural biogeographical barrier. A total of 361 host-seeking adult D. marginatus ticks from 31 sampling sites were analyzed, revealing 131 haplotypes for cox1 and 104 genotypes for ITS2. Neutrality tests and mismatch distribution patterns rejected the null hypothesis of the neutral theory, indicating that the population of D. marginatus in Anatolia has undergone a recent demographic expansion. Significant genetic differentiation and population structuring were observed between the Central and Northeastern Anatolian populations of D. marginatus, correlating with geographic distance and suggesting that the Anatolian Diagonal acts as a potential barrier to gene flow. Intrapopulation gene flow was higher in Central Anatolian populations compared to Northeastern Anatolian populations. Bayesian phylogeny revealed a highly divergent D. marginatus haplotype within the Northeastern Anatolian population, clustering into a Central Asian clade. Additionally, phylogenetic trees of the subgenus Serdjukovia revealed taxonomic ambiguities, including the absence of a distinct clade for D. niveus and potential misidentifications of D. marginatus and D. raskemensis specimens. Furthermore, the monophyletic relationship between D. marginatus and D. raskemensis supports the likelihood of sympatric speciation. These findings enhance our understanding of the genetic structure, phylogeography, and evolutionary dynamics of D. marginatus while providing a framework for future research on tick populations.

Dermacentor reticulatus - a tick on its way from glacial refugia to a panmictic Eurasian population

The ornate dog tick (Dermacentor reticulatus) shows a recently expanding geographic distribution. Knowledge on its intraspecific variability, population structure, rate of genetic diversity and divergence, including its evolution and geographic distribution, is crucial to understand its dispersal capacity. All such information would help to evaluate the potential risk of future spread of associated pathogens of medical and veterinary concern. A set of 865 D. reticulatus ticks was collected from 65 localities across 21 countries, from Portugal in the west to Kazakhstan and southern Russia in the east. Cluster analyses of 16 microsatellite loci were combined with nuclear (ITS2, 18S) and mitochondrial (12S, 16S, COI) sequence data to uncover the ticks' population structures and geographical patterns. Approximate Bayesian computation was applied to model evolutionary relationships among the found clusters. Low variability and a weak phylogenetic signal showing an east-west cline were detected both for mitochondrial and nuclear sequence markers. Microsatellite analyses revealed three genetic clusters, where the eastern and western cluster gradient was supplemented by a third, northern cluster. Alternative scenarios could explain such a tripartite population structure by independent formation of clusters in separate refugia, limited gene flow connected with isolation by distance causing a "bipolar pattern", and the northern cluster deriving from admixture between the eastern and western populations. The best supported demographic scenario of this tick species indicates that the northern cluster derived from admixture between the eastern and western populations 441 (median) to 224 (mode) generations ago, suggesting a possible link with the end of the Little Ice Age in Europe.

Borrelia and Other Zoonotic Pathogens in Ixodes ricinus and Dermacentor reticulatus Ticks Collected from the Chernobyl Exclusion Zone on the 30th Anniversary of the Nuclear Disaster

Background: The 26th of April 2016 marked 30 years since the Chernobyl accident has occurred in Ukraine. As a result, the uninhabited Chernobyl region has been directly exposed to ionizing radiation for >30 years. Most work has focused on identifying associations between levels of radiation and the abundance, distribution, and mutation rates of plants and animals. Much less, however, is known about microbial communities in this affected region. To date, there are no reports on the prevalence of any tick-borne pathogens in Ixodes ricinus ticks from the Chernobyl exclusion zone (CEZ). The objective of our study was to examine the abundance of I. ricinus and Dermacentor reticulatus ticks in the CEZ and to investigate the prevalence of Borrelia burgdorferi sensu lato (s.l.) and other zoonotic agents in these ixodid ticks. Methods: A total of 260 questing I. ricinus and 100 D. reticulatus adult ticks were individually polymerase chain reaction analyzed for the presence of Anaplasma phagocytophilum, Babesia spp., Bartonella spp., Borrelia burgdorferi s.l., Francisella tularensis, and/or Rickettsia spp. Results: The respective infections rates were identified and compared with those of ixodid ticks that were concurrently collected from Kyiv. The significant differences between the infection rates of the CEZ and Kyiv ticks were observed for Rickettsia raoultii in D. reticulatus ticks (53.0% vs. 35.7%, respectively; p < 0.05) and Bartonella spp. (8.1% vs. 2.7%; P < 0.05) in I. ricinus ticks. Conclusions: Although the current data clearly demonstrated that the prevalence of some zoonotic pathogens were significantly higher in the ixodid ticks from the CEZ, a more comprehensive systematic approach is required to examine the causal effect of long-term ionizing radiation on adaptive changes of tick-borne pathogens.