COS 120-10
Frequency-dependent selection on Borrelia burgdorferi is not supported by a mechanistic model and temporal infection data

Friday, August 9, 2013: 10:50 AM
L100A, Minneapolis Convention Center
Kimberly Tsao, Colorado State University, Fort Collins, CO
Durland Fish, Epidemiology of Microbial Diseases, Yale School of Public Health and Yale School of Medicine, New Haven, CT

Genetic diversity in the bacterium Borrelia burgdorferi, particularly at the outer surface protein C locus (ospC), has been proposed to be maintained by negative frequency-dependent selection. To test this hypothesis, in which host populations mediate selection by acquired immunity, we constructed a mechanistic model to simulate transmission of and selection on ospC genotypes in a community of vertebrate hosts. We also collected temporal field data from B. burgdorferi-endemic host populations to support model assumptions. 


Two necessary conditions that also determine the strength of negative frequency-dependent selection are: the duration of host immunity must last over three years, and these hosts must be responsible for 90% or more of all transmission. Comparisons of these conditions to our empirical observations suggest that frequency-dependence is not a strong selective mechanism in this system.