The genetic structure of Ixodes scapularis Say 1821 revisited

Although the genetic structure of Ixodes scapularis, the vector of Lyme disease in the eastern U. S., has already been the subject of several studies, none of the published information combines the analysis of maternally inherited (mitochondrial), and bi-parentally inherited (nuclear and microsatellite) markers on the same set of ticks. In addition, the geographical distribution of the analyzed samples was often partial and did not cover the whole range of I. scapularis. We collected a sample of 350 ticks from 17 states. The small ribosomal subunit (12SrRNA), the control region (d-loop) and the ribosomal internal transcribed spacer regions (ITS2) of each tick were sequenced and compared in order to establish if mitochondrial and nuclear gene sequences provide the same information. In addition, 9 microsatellite markers were genotyped. Our preliminary data are showing that the tick is subdivided in 5 mitochondrial clades, which can be tracked back to biogeographical events of the Quaternary.  The ITS2 sequences are very conserved and do not differentiate the same groups, while further suggesting a very recent dispersal of this tick species. The microsatellite markers corroborate nuclear data by showing very little geographical differentiation, persistent gene flow between populations, and no support for the mitochondrial clade subdivision.