Population genetic analyses of chewing lice parasitizing pocket gophers

Lice (Ischnocera: Trichodectidae) are relatively well-known ectoparasites that parasitize only mammals, specifically pocket gophers in the rodent family Geomyidae. Because parasites depend upon their hosts for survival, they often have complex ecological interactions with their hosts that persist over long evolutionary timescales. Host-parasite systems and their histories between can be used to analyze a variety of ecological and evolutionary questions. Due their conservative morphology and resulting limited dispersal ability, pocket gophers have been documented to have long-term associations with their parasites, specifically lice. This research is concentrated on the population genetics of louse populations, and to determine the microevolutionary processes driving macroevolutionary patterns such as cospeciation in gopher-louse assemblages. Chewing lice (Geomydoecus ewingi) parasitizing the Baird’s pocket gopher (Geomys breviceps) were examined. Ten gophers and their lice were collected from three localities in College Station, Texas. A novel genomic microsatellite library was constructed from G. ewingi  lice for the purpose of creating loci specific primers. Ten to 20 lice were sampled from three gophers at each of the three geographic localities. DNA was isolated from each louse using louse-specific protocols.  Lice were screened for each of the 13 polymorphic loci using PCR reactions. Out of the 13 polymorphic loci, 10 were analyzed. Population structure was assessed using F_ST statistics, as well as analysis of molecular variance. The patterns of population clustering among G. ewingi individuals was obtained using STRUCTURE. AMOVA analyses indicated the majority of the genetic variation existed within individuals. STRUCTURE analyses identified two genetic clusters. The findings suggest there is hierarchical structuring of louse genetic diversity, which generally corresponds to geography rather than host individuals.