Comparison and complete mitogenomes of two morphologically similar but ecologically different tick species, Ixodes arboricola and Ixodes lividus (subgenus Pholeoixodes)

Ixodes arboricola and Ixodes lividus are ornithophilic tick species. The former is typically associated with tree-hole dwelling birds, while the latter is a host-specific parasite of sand martins (Riparia riparia). These two tick species share important morphological characters that make them difficult to identify when they are collected from atypical hosts, such as birds of prey. Despite this, high resolution digital pictures have not been reported to compare I. arboricola and I. lividus, nor was their complete mitogenome reported. The aim of this study was to compensate for this lack of illustrations and sequence data. Nymphs and females of I. arboricola and I. lividus were used for morphological comparison, and one specimen of each species to generate mitogenome sequences. The results showed that females of these two species are different in the shape of their scutum, porose areas, the length of basis capituli, palps, coxae, genital pore, anal groove and tarsus I. On the other hand, nymphs of I. arboricola and I. lividus can be distinguished according to their cervical grooves, cornuae, auricular ridges and spiracular plates. The mitochondrial genome size was 14,539 and 14,536 bp, for I. arboricola and I. lividus, respectively. The mitogenome sequences of I. arboricola and I. lividus were 91.1% identical to each other. Phylogenetic analysis of Ixodes species showed that I. arboricola and I. lividus are sister species, and cluster together with Ixodes crenulatus/canisuga under strong support. In conclusion, results of this study confirmed that the front of the basis capituli is crucial in distinguishing Ixodes species, especially in the subgenus Pholeoixodes where these two species are phylogenetically closest related to I. canisuga. Another phylogenetically relevant morphological character is the scutal surface which is wrinkled (rugose) as a common feature of Pholeoixodes species in the clade of I. arboricola and I. lividus (including I. canisuga, I. rugicollis and I. ariadnae). Although the host ranges of I. arboricola and I. lividus do not substantially overlap, they may transmit some of the shared pathogens. Relevant data indicate that the eco-epidemiological significance of the two ornithophilic tick species studied here may in part be similar and they may play a role in the transmission of rickettsiae, borreliae and viruses of which birds act as reservoirs.