COII variation within and among populations of black-tailed prairie dogs (Cynomys ludovicianus) and their fleas (Pulex simulans): A case for coevolution

The effects of habitat islands (isolation-by-distance) on demic variation in the mitochondrial COII gene of Pulex simulans associated with black-tailed prairie dogs (Cynomys ludovicianus) were examined. Prairie dog colonies have been significantly reduced and fragmented in Texas within the past 100 years due to urbanization and agricultural practices. Prairie dog colonies also represent behavioral islands (isolation due to the harem polygynous nature and coterie structure of the host). Migration among the colonies studied is no longer possible, creating a potential for genetic diversification in both the host and parasite.; The entire COII gene from P. simulans and C. ludovicianus was sequenced and found to be 687 bp and 684 bp, respectively. While the 5' and 3' ends of the gene were highly conserved, there was significant variation in the middle portion of the gene that was useful. Most sequences were unique haplotypes. We found that the amount of sequence variation in Pulex, among colonies, was low, indicating that migration of parasites due to transient-host association (e.g. coyotes, etc.) is minimal. The majority of the variation in the COII gene in Cynomys and Pulex was attributable to within-population variation (Fn = 0.1214 and Fn = 0.0770, respectively). Levels of variation, within colonies, were high, indicating that the response to recent habitat fragmentation is not complete. 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 each organism.; 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 gene topologies are not congruent (i.e., not a "one-for-one" relationship), a Mantel test indicates that there is significant correlation (p = 0.04) in the patterns of genetic divergence of Cynomys and Pulex. The concept of colonization is a plausible explanation for the maintenance of polymorphic alleles within these populations that exhibit absent gene flow.