COII variation within and among populations of black-tailed prairie dogs (Cynomys ludovicianus) and their fleas (Pulex simulans): A case for coevolution?
Prairie dog (Cynomys ludovicianus) colonies have been significantly reduced and fragmented in Texas within the past 100 years, due to encroaching urbanization and agricultural domination. Isolation resulting from this fragmentation is reinforced by the harem polygynous behavior of prairie dogs and their coterie structure. These interactive factors have created habitat islands (isolation-by-distance) among what were once contiguous demes.
Migration among the colonies is no longer feasible, creating a potential for genetic diversification in the prairie dog coteries and also in their parasitic associates. The genetic consequences of habitat islands, as measured by mitochondrial COII gene variance, were examined in black-tailed prairie dogs and their most common ectoparasite, Pulex simulans.
The entire COII gene from C. ludovicianus and P simulans was sequenced and found to be 684 and 687 bp in length, respectively. While the 5' and 3' ends of the gene were highly conserved, there was substantial variation in the middle portion of the gene that was informative about these relationships at the populational level.
The majority of the variation in the COII gene in Cynomys and Pulex was attributable to within-population variation (Fs,= 0.12 and Fst= 0.07, respectively). The level of variation within colonies was high, indicating that the response to recent habitat fragmentation has not lead to allelic fixation. The possibility of recolonization cannot be ruled out, however, as an explanation for the maintenance of polymorphic alleles within these populations.
Using a combination of tree construction methods (consensus tree and neighbor-joining tree) and multidimensional scaling, the center of dispersions of the metapopulation could be assigned for both prairie dogs and fleas.
In addition to assessing the amount of COII variation within and among populations, this dissertation focused on the assessment of coevolutionary patterns in this complex host-parasite system. Although the COII host-parasite topologies are not completely congruent, a Mantel's test indicated that there is a significant correlation (p=0.04) in host-parasite genetic divergence.