Genetic Variation in the Tick \u3cem\u3eIxodes scapularis\u3c/em\u3e Detected Using SSCP

Blacklegged tick (Ixodes scapularis) is the primary vector of the Lyme disease agent, Borrelia burgdorferi. It is hypothesized that the amount of genetic variations in the spirochete Borrelia burgdorferi may be correlated with the amount of variations in the tick vectors. In order to test this hypothesis, the genetic variations of Ixodes scapularis among populations from the barrier islands in South Carolina, Georgia, and Florida were investigated using DNA single strand conformation polymorphism (SSCP). The SSCP targeted two DNA regions, one from the ribosomal internal transcribed spacer 1 (ITS1) in the diploid nuclear genome and the other from the cytochrome b in the haploid mitochondrial genome. A total of 768 adult ticks were collected from 10 islands along the Atlantic coast in three states and were investigated by SSCP. Seven haplotypes were identified using a 276 bp region of the CTB gene, and 13 genotypes were identified using 340 bp region of ITS1. The largest genetic distance was found to be between Edisto Island, SC and Pritchard\u27s Island, SC, indicating that the ticks in this state have undergone much more divergence than those ticks found in Georgia and Florida. Ticks from three islands in Florida clustered together and ticks from both islands in Georgia clustered together with ticks from one island in Florida. Significant variation was shown to exist in the haplotypes and genotypes of the ticks from South Carolina, Georgia, and Florida. These results also indicate that gene flow is or was occurring in the populations; however there was also an indication of a high amount of inbreeding. Genetic clinal variation was suggested by the data. These results may suggest that the population of ticks in South Carolina are older than those in Georgia and Florida due to the greater amount of variation found in tick populations in South Carolina