Of genes and ticks: The population genetics of Dermacentor variabilis and Ixodes texanus infecting a wildlife host
Abstract
Ticks, major vectors of diseases affecting humans and animals, are increasingly becoming the focus of population genetic research. The major objective of this thesis was to elucidate the population genetic patterns exhibited by two ticks, Dermacentor variabilis and Ixodes texanus , at the scale of the host population (component population, CP) and individual host (infrapopulation, IP). I isolated novel microsatellites from these two species and preliminary analyses of the data revealed significant deviations from Hardy-Weinberg Equilibrium (HWE) expectation at the scale of the CP in both species. Through a quantitative review I found that deviations from HWE was common in parasites, since the probability of deviating from HWE as well as magnitude of such deviation was higher in the case of microsatellites isolated from a wide taxonomic array of parasites vs. mammals. I thus tested four hypotheses that could explain deviations from HWE in D. variabilis and I. texanus, these were: the presence of null alleles, Wahlund effect, kin group structure or inbreeding. These findings are discussed with respect to parasites in general and the life-history characteristics of two ticks in particular. ^ Finally, I evaluated two hypotheses at the scale of the I. texanus IP. First, using Monte-Carlo simulation I found evidence for the hypothesis that small IPs could be viewed as subsamples of larger IPs with regard to two genetic parameters: FISi (extent of deviation in HWE at the IP scale) and μAR (average allelic richness). Using a second Monte-Carlo simulation, I rejected the hypothesis that the pattern of FISi and μAR across individual hosts could be explained by panmixia at the scale of the CP. However, I found evidence that a single global level of inbreeding could explain the statistical patterns of the two genetic parameters at the IP scale. These findings are discussed in terms of general parasite biology and the life-history characteristics of I. texanus.^
Degree
Ph.D.
Advisors
Olin E. Rhodes, Purdue University.
Subject Area
Biology, Entomology|Agriculture, Forestry and Wildlife|Biology, Parasitology
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