Species Diversity and Host Specificity in Flea Communities from the Two Subspecies of the Gunnisonu27s Prairie Dog (Cynomys gunnisoni)

摘要

In 2008, Gunnison’s prairie dog (Cynomys gunnisoni) (GUPD), became a candidate species for listing under the Endangered Species Act (ESA) within the montane (2,300 to 3660m) region of its range due to a higher prevalence of plague and unstable population structures. The geographic division of the GUPD range into the montane and prairie regions also serves to divide the GUPD into two historically defined subspecies: the Gunnison (Cynomys gunnisoni gunnisoni) in the montane region and the Zuni (Cynomys gunnisoni zuniensis) in the prairie region. To help evaluate why there is a difference in the prevalence of plague, it is important to look at the fleas that serve as vectors of plague. The fleas that persist on GUPD serve as vectors for pathogens, including Yersinia pestis (the causative agent of plague) and Bartonella spp., among individual prairie dogs and colonies. Analysis of the sequence of a key mitochondrial gene, cytochrome oxidase subunit II (COII), for 63 sampled fleas was used to characterize the number and type of flea species, or flea diversity, occurring on GUPD and whether these fleas tend to specialize on a particular GUPD subspecies. The level to which a parasite, such as a flea, specializes on a host is called host specificity. This evaluation of species diversity indicates the occurrence of a new subspecies of Oropsylla hirsuta, three genetically undescribed Oropsylla species, and one undescribed Pulex species that all occur on GUPD. The evaluation comparing the frequency of the flea species occurring on each GUPD subspecies showed that there is not significant differentiation of fleas species between the two subspecies. This suggests that fleas do not discriminate between the two subspecies. This lack of host specificity may have important implications for the spread of plague between subspecies. An Analysis of Molecular Variance (AMOVA) revealed that most of the genetic variation in the COII sequences exists among fleas occurs within a colony, and that there is also significant variance among colonies. Thus, there appears to be no genetic break in the fleas that corresponds to the subspecies distinction in GUPD. The colonies differed greatly in the amount of genetic diversity that was estimated to be present and it was found that the number of prairie dog hosts sampled from each colony was the best explanation of the genetic diversity observed. The more prairie dog host sampled from a colony, the more genetic diversity was measured in that colony. The new undescribed flea species and the lack of host specificity of fleas on the two species are important in understanding the apparent differences in susceptibility to plague between the two GUPD subspecies, and the movement of fleas and the pathogenic bacteria between the two subspecies. Subsequent studies that evaluate the presence of pathogenic bacteria in the fleas sampled need to be completed to know the full implications of these results and how they may inform conservation efforts.