PMC

Map displays collections sites for I. scapularis from the Northeastern (NY1; MA, CT, LI2), Southeastern (NC1; NC2; SC98) and Midwestern US (Stockton, Colfax, Marinette); and for B. burgdorferi populations from the Northeastern (NY1; VA) and Midwestern US (Stockton, Colfax, Marinette). Approximate glacial maximum of the Pleistocene ice sheet is drawn, after Church (2003) and .

Bayesian posterior probability surface of the estimate of the population growth rate (g) for I. scapularis and B. burgdorferi populations. The Most-Probable Estimates (MPE) of g lie at apex of each curve. A. Estimates of g for individual I. scapularis populations from each region. Growth estimates for Northeast and Southeast populations coincide with previous reports (). B. Estimates of g for B. burgdorferi populations grouped by region. The lower chart displays estimates of g for Northeastern B. burgdorferi with RST-I haplotypes removed (n=15) and RST-I haplotypes alone (n=15).

Cladogram and frequency distribution of B. burgdorferi IGS haplotypes collected from Virginia (VA), New York (NY), and three Midwestern sites (Sto, Mar, Co). A. Bayesian cladogram of IGS haplotypes with posterior probability values reported for each node. B. Haplotype frequency distribution with gray shading indicating types shared between Northeastern and Midwestern sites. C. Previously described haplotypes in . Haplotypes found only in our Midwestern samples but previously found in Northeastern samples () are marked with an asterisks. The haplotype of the B31 type strain is marked with a cross.

Minimum Spanning Tree (MST) of I. scapularis and B. burgdorferi haplotypes. Each line connecting haplotypes represents one mutational change. Haplotype size reflects relative sampling frequency. A. I. scapularis haplotype MST. SE=Southeast, NE=Northeast, MW=Midwest. Haplotypes 10 and 22 from the Midwest, haplotypes K, L, LI-4; LI-9; and NY-11 from the Northeast, and haplotypes NC2-22 and NC2-29 from the Southeast are each one mutation away from 1/F and are not shown. B. B. burgdorferi IGS haplotype MST. Haplotype named according to where possible. VA=Virginia, NY=New York, MW=Midwest. Haplotypes 16 (2d), 3 (6a), 1 (7a) are not present in the Northeastern sample although initially described in a previous Northeastern sample are marked with an asterisks ().