Genetic analysis of recently established Ixodes scapularis populations in North Dakota

The blacklegged tick, Ixodes scapularis, is the most medically significant vector of arthropod borne-diseases in North America, including Borrelia burgdorferi, the causative agent of Lyme disease. Tick surveillance in eastern North Dakota has revealed the presence of established I. scapularis populations in habitats previously regarded as unsuitable for this species. Understanding the population structure of this vector is essential to predicting the possible expansion of blacklegged tick populations and the associated pathogens. We investigated the genetic structure of ‘founder’ populations of I. scapularis in North Dakota by comparing the sequences of a 600-base pair region of the COI gene in individual ticks collected in eastern North Dakota with homologous sequences in ticks collected in eastern USA and Canada. Results revealed differences in haplotype frequencies in North Dakota ticks vs. ticks collected in eastern USA and Canada. Few closely related haplotypes accounted for the majority of I. scapularis found within North Dakota, whereas the diversity of haplotypes was higher in tick populations from eastern USA and Canada. Statistical analyses of genetic variance suggest that I. scapularis populations in eastern North Dakota are recently established and currently undergoing expansion. This study provides insight as to the source of founders for these newly established populations and, coupled with an increased understanding of the severity of ecological constraints placed on these populations, will help define the future distribution and epidemiology of tick-borne diseases in north central USA and Canada.