Post-Plague Recolonization in Black-Tailed Prairie Dogs

Due to the recent introduction of pathogens such as Yersinia pestis, the causative agent of the plague, natural populations of black-tailed prairie dogs (Cynomys ludovicianus) are increasingly threatened. Prairie dogs are extremely vulnerable to plague, and colonies may be extirpated following exposure to the bacterium. Repopulation of extinct colonies allows immigrants to leave nearby crowded colonies, and leads to questions about the influence of plague on the evolution of prairie dog populations. The goal of this project is to explore the genetic effects of re-colonization after plague in prairie dogs. Specifically, I will determine the colony of origin of all founders, which will allow estimates of the degree of inbreeding in newly founded colonies. I will also estimate the extent of founder effects, which arise from small populations with low genetic diversity that are subject to inbreeding, disease, and a suite of other stochastic environmental and genetic processes. Finally, I will examine the effect of plague on genetic diversity by comparing heterozygosity of colonies before and after plague events. Prairie dogs were trapped at 10 colonies in Boulder County, and blood, tissue and ectoparasites were collected. Each animal was marked with a unique tag for future identification and estimates of survival and dispersal. All individuals were genotyped at 18 microsatellite loci. Comparisons will be made among colonies founded since extirpation in 2005 or 2006, populations re-colonized after a plague epidemic in 1994, and those that have no record of being affected by plague. Introduction Highly social species such as prairie dogs are hypothesized to have higher disease transmission, thus suggesting an important role of disease in the evolution of social species (). More (). Introduced pathogens offer a unique opportunity to examine how naïve species will respond to a novel threat, and whether social species are indeed more vulnerable to pathogens. The existence of plague in prairie dogs thus provides a means of testing whether a novel pathogen provokes an evolutionary response in a colonial species. The dynamics of plague are poorly understood, but what is clear is the rapidity with which it extirpates prairie dog colonies. Plague is transmitted by fleas, which prairie dogs may harbor in high numbers, and once the first prairie dog contracts the disease, it is only a matter of weeks before the entire colony dies out. Given that plague decimates entire colonies in such a short time, it seems likely that plague can be considered an evolutionary force in prairie dogs. Because plague eliminates entire populations, which are then recolonized, populations undergo extreme bottlenecks as a result. Plague is therefore expected to have genetic consequences on the affected colonies, including a decrease in genetic diversity both at the colony level due to the bottleneck and founder effects, and at the individual level due to inbreeding that likely results from a founder effect. This depression of genetic diversity may be exacerbated if continued immigration occurs from only one or few source colonies. Populations that have been subjected to repeated plague outbreaks are expected to possess lower diversity than those that have undergone bottlenecks only once, and colonies that have never experienced plague should be unaffected. The aim of this study is to determine the extent to which plague influences the evolution of prairie dogs on short time scales. To answer this question, I will investigate changes in genetic diversity after recolonization following plague extirpations. I will also determine the origin of population founders and immigrations rates to estimate the degree of inbreeding expected in recolonized populations.