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Genetic Characterization of Baylisascaris Procyonis and Related Species

出版	University of California, Davis, 2016
ISBN	13696167839781369616781
URL	http://books.google.com.hk/books?id=Na6FtAEACAAJ&hl=&source=gbs_api

註釋Baylisascaris spp. are nematode parasites that primarily use carnivorans as definitive hosts. Eleven species have been described, and the most studied species is B. procyonis, or raccoon roundworm. The focus on B. procyonis is because this parasite occurs in raccoons throughout their native range, often at high prevalence, and because numerous small mammals, birds, and accidentally infected humans are susceptible to pathogenicity following infection due to aggressive larval migration through host tissues. Research on Baylisascaris species often focuses on determining lifecycle characteristics or estimating prevalence in nature based on necropsies or fecal samples. However, limited work has been done on genetic characteristics of B. procyonis or other Baylisascaris species, meaning that we do not have a full picture of the evolutionary relationships among species, nor do we have information on baseline genetic structure for the most common species, B. procyonis. In Chapter 1, evolutionary relationships within the genus Baylisascaris were examined using eight genetic markers, including three single- or low-copy nuclear loci. Seven species of Baylisascaris were included in this analysis, with two species - B. devosi and B. tasmaniensis - having no previously published genetic data. Results supported monophyly of Baylisascaris, but two closely related species, B. columnaris in skunks and B. procyonis in raccoons, could not be reliably distinguished based on the genetic markers used. Analysis using a Bayesian species delimitation program provided weak evidence to support B. columnaris and B. procyonis as separate species. Chapters 2 and 3 focused on population genetic analyses of the most common species, B. procyonis at microgeographic and macrogeographic scales. In Chapter 2, B. procyonis specimens from 18 raccoon hosts collected from southeast Santa Barbara County, CA were analyzed. Worms within hosts (infrapopulations) were found to be more related than expected based on the composition of the component population. Comparing infrapopulations of related worms creates biased samples that affect analyses of population genetic structure. The degree of relatedness of parasites within infrapopulations needs to be tested prior to conducting population genetic analyses. In Chapter 3, samples of B. procyonis obtained from 12 states and two Canadian provinces were analyzed for population genetic structure at a macrogeographic scale. Due to characteristics of B. procyonis and its hosts, reduced structure may be expected, even at a large scale. Results supported two major genetic clusters separated by the Rocky Mountains, with some support for additional clusters based on geographical separation. Pairwise FST values for a pattern of six clusters were significant, and ranged from 0.078 to 0.364. Gene flow among inferred clusters may be due to raccoon movement or to movement of infected bird and small mammal paratenic hosts.