Development and testing of microsatellite loci for the study of population genetics of Ixodes ricinus Linnaeus, 1758 and Ixodes inopinatus Estrada-Peña, Nava and Petney, 2014 (Acari: Ixodidae) in the western Mediterranean region

Abstract

Ixodes ricinus is an important vector of several human and veterinary infectious agents. Its wide geographical distribution and permissive feeding behaviour have prompted earlier studies on its population genetics. Results were, nevertheless, not conclusive. Furthermore, no research has fully focused on the south-western distribution range of I. ricinus, where exchanges between European and North African populations are more likely to occur. The presence of an additional species, Ixodes inopinatus, in the area further confuses the topic, as the two species are hard to differentiate morphologically. The present work describes the testing of microsatellite markers previously described for I. ricinus using Portuguese and Tunisian tick populations of both species. In addition, new microsatellite loci were developed to complement the available marker toolbox. Loci showed different amplification successes across subpopulations, with Tunisian DNA less readily amplified. Altogether, 15 loci were considered suitable for genetic analyses of Portuguese subpopulations, 10 for Tunisian samples, and seven, common to both populations, were considered to be informative at the inter-continental level. A preliminary analysis of both datasets revealed two isolated populations, which can correspond to two different species. Furthermore, Tunisian specimens identified by sequencing of 16S rDNA as having I. ricinus or I. inopinatus sequence profiles all clustered together in one single population using the proposed microsatellites. This confirms that taxonomic decisions based only on 16S rRNA gene sequencing can be misleading. The application of the proposed set of microsatellite markers to a larger sample, representative of the south-western Ixodes’ distribution range, will be crucial to clarify the distribution of both species.