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Upper Respiratory Microbes in North American Tortoises (Genus Gopherus)
AuthorWeitzman, Chava Leah
AdvisorTracy, Richard C.
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Infectious disease can play a vital role in species conservation, as some diseases can cause massive population die-offs. In North American tortoises, population declines have been attributed to an upper respiratory tract disease, but the importance of this disease within and among tortoise hosts is controversial. In this dissertation, I use samples from the upper respiratory tract of wild tortoises representing multiple species in the genus Gopherus to answer questions regarding pathogen prevalence and co-infection, pathogen genetic diversity, and the ecology of pathogens within the upper respiratory tracts of tortoises. Using genetic methods including polymerase chain reaction (PCR), quantitative PCR, Sanger sequencing, and 454-pyrosequencing, the data presented herein supports hypotheses that pathogens in this disease system interact with each other and with other microbes in the respiratory tract differently in different tortoise host species.In this system, both transmission and disease progression are found to be extremely slow in these long-lived hosts. Though pathogens were widespread among the sampled tortoises, few individuals were found with clinical signs of disease. Few individuals capable of transmitting disease (requiring nasal mucus and pathogen), along with few opportunities for pathogen transmission (requiring long periods of direct contact), indicate that it is unlikely for tortoises to fully clear themselves of these microbes without risk of the pathogen’s extinction. If this is the case, then it is likely that more tortoises than we can detect have these microbes in their upper respiratory tracts. With this in mind, and considering the abundance of visibly healthy tortoises over ill tortoises, my collaborators and I suspect that pathogens in this system likely form commensal relationships with their hosts much of the time, until a stressor alters the system and leads to a parasitic interaction.The results of this dissertation indicate that this disease is context dependent, depending on the host and likely other microbes in the community. Our understanding of the ecology of this disease system would greatly benefit from experimental inoculation and long-term resampling studies.