The Ixodes ricinus group of ticks in the western Mediterranean region and north Africa: new insights in to their population genetics and microbiome fauna.

In Europe and northern Africa, the tick Ixodes ricinus is the most important arthropod vector of diseases. It transmits several agents of medical and veterinary importance. Among the most important human tick-borne diseases associated with I. ricinus are Lyme borreliosis, Spotted Fever Group rickettsiosis, Human Anaplasmosis, Human Babesiosis and Tick-borne Encephalitis. For each of these diseases, I. ricinus is known to carry different pathogenic genospecies, strains or geographic variants. I. ricinus is considered a classic example of an extreme generalist vector, known for being unspecific in terms of host choice. During its life, several vertebrates are used as feeding hosts like mammalian, including humans, avian and reptilian species. Previous studies, have indicated that I. ricinus and other tick species are subdivided in genetically identifiable subpopulations: depending on the tick species, populations may be geographically structured or they may differ in their association to hosts, sex and/or pathogens. These populations, depending on their different interaction with the environment and their hosts, are also not all equally competent vectors for the different pathogens. Previous enzymatic and genetic studies on I. ricinus from Europe showed a relative lack of genetic structure within European populations, and a distance between European and African populations of I. ricinus. Genetically distant North-African populations might correspond to the recently described, Ixodes inopinatus, a species belonging to the I. ricinus complex, from southern Spain,Portugal and northern Africa. The real distribution of this new taxon and if they transmit distinct groups of pathogens needs to be determined, as this tick has probably been incorrectly identified as I. ricinus in past studies. The studies on genome organization and population structure will advance research aiming at determining the genetic basis of tick phenotypic and behavioral differences. Also, ongoing research efforts are targeting the microbiome of ticks to find a possible way of using micro-organisms to disrupt transmission cycles. A more thorough understanding of the microbiota composition and of the dynamic interactions between microbial elements within tick species, might allow the future implementation of innovative biological strategies for tick control. In this project, we propose a study I. ricinus/I. inopinatus population from Portugal, Spain and Tunisia using next generation sequencing NGS in analyzing the intraspecific genetic variability of tick species and the analysis of microbiota composition. Also, we propose laboratory cross-breeding experiments to verify whether the two species can produce viable offspring. The clear identification of tick species/subpopulations is a crucial step towards a better understanding of the transmission cycles of pathogens occurring in nature and for an informed evaluation of the epidemiological risk factors in the studied area.