HOST MOVEMENT AND THE GENETIC-STRUCTURE OF POPULATIONS OF PARASITIC NEMATODES

Mitochondrial DNA (mtDNA) sequence data were used to compare the popul ation genetic structures of five species of parasitic nematodes from t hree different hosts: Ostertagia ostertagi and Haemonchus placei from cattle, H. contortus and Teladorsagia circumcincta from sheep, and Maz amastrongylus odocoilei from white-tailed deer. The parasites of sheep and cattle showed a pattern consistent with high gene flow among popu lations. The parasite of deer showed a pattern of substantial populati on subdivision and isolation by distance. It appears that host movemen t is an important determinant of population genetic structure in these nematodes. High gene flow in the parasites of livestock also indicate s great opportunity for the spread of rare alleles that confer resista nce to anthelmintic drugs. All species, including the parasite of deer , had unusually high within-population diversities (averages of 0.019- 0.027 substitutions per site between pairs of individuals from the sam e population). Large effective population sizes (Ne), perhaps in combi nation with rapid mtDNA evolution, appear to be the most likely explan ation for these high within-population diversities.