Host-associated differentiation (HAD) in Dermacentor variabilis and the examination of HAD in two other common tick species in the US (Acari: Ixodidae)

The American dog tick, Dermacentor variabilis, is the primary vector of tularemia and Rocky Mountain spotted fever in its’ range. D. variabilis feeds on a wide variety of hosts. Usually the immature stages feed on small mammals while adults feed on medium-sized mammals. Previous population genetic studies on this tick focused on geographic differentiation. However, genetic variation can be associated with host species. The existence of genetically distinct populations associated with host species is called host-associated differentiation (HAD). In this study, ticks were collected from different vertebrate hosts to test for HAD using SNPs. 1,326 D. variabilis ticks were collected from 15 mammal species out of 570 individual mammal hosts that were caught in the field. DNA extractions were optimized for ddRADseq Illumnia sequencing and bioinformatic analyses completed. It was found that D. variabilis is exhibiting HAD. D. variabilis had the highest amount of differentiation when comparing ticks from opossums to ticks from harvest mice. In addition, we hypothesize that the HAD patterns also correlate with host nesting habits as the genetic differentiation varied accordingly. Ixodes scapularis and Amblyomma americanum ticks from hosts were also sequenced to test for HAD, and results will be discussed. Characterizing genetically distinct populations of vectors is essential for understanding disease transmission and the implementation of targeted control efforts.