Ixodes inopinatus cannot be distinguished from I. ricinus by the sole use of the 16S ribosomal gene

International audienceThe most common and studied tick species in Europe is by far Ixodes ricinus, an exophilous species with catholic feeding behaviour and a major vector for numerous tick-borne diseases. The development of molecular markers has recently improved our knowledge of the intra- and interspecific genetic variability for the different Ixodes species within the ricinus complex and their systematics. In particular, North African populations have revealed marked genetic divergences with European populations of I. ricinus using the sequences from 6 different genes (Noureddine et al. 2011). By using both morphological and molecular data (albeit restricted to partial sequence of the 16S gene only), Estrada-Peña et al. (2014) have described a new species, I. inopinatus, mostly occurring in north Africa but also considered to have been found in a few other locations in Europe. Since this description of a new Ixodes species in western Palearctic, a growing number of publications have reported I. inopinatus in additional locations in Europe (Germany, Romania) identified using 16S sequences. Using the dataset provided in Noureddine et al. 2011, we demonstrate that the 16S gene does not allow recognizing a distinct and robust monophyletic clade gathering all the north African individuals to the exclusion of all European samples. By contrast, the other coding genes (Co1, but even more efficiently Defensin, TROSPA and EF1α) allow clustering all the North African individuals to the exclusion of all European ones. More recently, a set of more than 100 SNPs spread all over the genome (Quillery et al. 2014) has confirmed the marked genetic divergence between I. inopinatus and I. ricinus and suggests that there is no introgression of the genes of the first species into Europe (Poli et al. 2020). Although additional investigations remain to be conducted to identify morphological differences between the two taxa as well as their potential interfertility, we argue that I. inopinatus cannot be distinguished from I. ricinus by the use of the sole 16S ribosomal gene. Likewise, the existing 16S sequences assigned to inopinatus available in GenBank should be taken with caution, especially the European one