Ecological and Evolutionary Dynamics of Complex Host-Parasite Communities

Parasites are ubiquitous in nature, and embedded in complex communities of hosts and parasites. Most parasite species infect multiple host species, and most host species are infected by multiple parasite species. However, it’s very challenging to study the complex web of host- parasite interactions in natural settings, and controlled lab experiments are often limited to small numbers of host or parasite species. Additionally, parasites can evolve rapidly, so host-parasite interactions change over time. In my dissertation, I used field surveys, network analyses, and lab experiments to understand how different host species influence parasite infections in another host species, how parasites differ in their ability to infect multiple host species, how hosts respond to the threat of multiple parasites, and how parasites evolve over the course of an epidemic. My general aims were to untangle the web of interactions in host-parasite communities and to understand the evolutionary consequences of those interactions. In Chapter 2, I estimated potential cross-species transmission of different parasite species and built networks of hosts and parasites connected by these interactions. In Chapter 3, I investigated the consequences of multiple parasites on host behavior, namely sexual reproduction. Lastly, in Chapter 4, I looked to see if parasites were evolving in response to ecological dynamics such as the growth phase of an epidemic. Overall, I found that particular host and parasite species may disproportionately contribute to cross-species transmission, hosts alter their reproductive behavior in response to biotic factors, and parasite virulence can evolve rapidly over the course of a natural epidemic.PHDEcology and Evolutionary BiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163257/1/cgowler_1.pd

An interactive patient transfer network and model visualization tool for multidrug-resistant organism prevention strategies

Background: The CDC’s new Public Health Strategies to Prevent the Spread of Novel and Targeted Multidrug-Resistant Organisms (MDROs) were informed by mathematical models that assessed the impact of implementing preventive strategies directed at a subset of healthcare facilities characterized as influential or highly connected based on their predicted role in the regional spread of MDROs. We developed an interactive tool to communicate mathematical modeling results and visualize the regional patient transfer network for public health departments and healthcare facilities to assist in planning and implementing prevention strategies. Methods: An interactive RShiny application is currently hosted in the CDC network and is accessible to external partners through the Secure Access Management Services (SAMS). Patient transfer volumes (direct and indirect, that is, with up to 30 days in the community between admissions) were estimated from the CMS fee-for-service claims data from 2019. The spread of a carbapenem-resistant Enterobacterales (CRE)–like MDROs within a US state was simulated using a deterministic model with susceptible and infectious compartments in the community and healthcare facilities interconnected through patient transfers. Individuals determined to be infectious through admission screening, point-prevalence surveys (PPSs), or notified from interfacility communication were assigned lower transmissibility if enhanced infection prevention and control practices were in place at a facility. Results: The application consists of 4 interactive tabs. Users can visualize the statewide patient-sharing network for any US state and select territories in the first tab (Fig. 1). A feature allows users to highlight a facility of interest and display downstream or upstream facilities that received or sent transfers from the facility of interest, respectively. A second tab lists influential facilities to aid in prioritizing screening and prevention activities. A third tab lists all facilities in the state in descending order of their dispersal rate (ie, the rate at which patients are shared downstream to other facilities), which can help identify highly connected facilities. In the fourth tab, an interactive graph displays the predicted reduction of MDRO prevalence given a range of intervention scenarios (Fig. 2). Conclusions: Our RShiny application, which can be accessed by public health partners, can assist healthcare facilities and public health departments in planning and tailoring MDRO prevention activity bundles

Data from: Disease ecology across soil boundaries: effects of below-ground fungi on above-ground host–parasite interactions

Host–parasite interactions are subject to strong trait-mediated indirect effects from other species. However, it remains unexplored whether such indirect effects may occur across soil boundaries and connect spatially isolated organisms. Here, we demonstrate that, by changing plant (milkweed Asclepias sp.) traits, arbuscular mycorrhizal fungi (AMF) significantly affect interactions between a herbivore (the monarch butterfly Danaus plexippus) and its protozoan parasite (Ophryocystis elektroscirrha), which represents an interaction across four biological kingdoms. In our experiment, AMF affected parasite virulence, host resistance and host tolerance to the parasite. These effects were dependent on both the density of AMF and the identity of milkweed species: AMF indirectly increased disease in monarchs reared on some species, while alleviating disease in monarchs reared on other species. The species-specificity was driven largely by the effects of AMF on both plant primary (phosphorus) and secondary (cardenolides; toxins in milkweeds) traits. Our study demonstrates that trait-mediated indirect effects in disease ecology are extensive, such that below-ground interactions between AMF and plant roots can alter host–parasite interactions above ground. In general, soil biota may play an underappreciated role in the ecology of many terrestrial host–parasite systems

Density, parasitism, and sexual reproduction are strongly correlated in lake Daphnia populations

Many organisms can reproduce both asexually and sexually. For cyclical parthenogens, periods of asexual reproduction are punctuated by bouts of sexual reproduction, and the shift from asexual to sexual reproduction has large impacts on fitness and population dynamics. We studied populations of Daphnia dentifera to determine the amount of investment in sexual reproduction as well as the factors associated with variation in investment in sex. To do so, we tracked host density, infections by nine different parasites, and sexual reproduction in 15 lake populations of D. dentifera for 3 years. Sexual reproduction was seasonal, with male and ephippial female production beginning as early as late September and generally increasing through November. However, there was substantial variation in the prevalence of sexual individuals across populations, with some populations remaining entirely asexual throughout the study period and others shifting almost entirely to sexual females and males. We found strong relationships between density, prevalence of infection, parasite species richness, and sexual reproduction in these populations. However, strong collinearity between density, parasitism, and sexual reproduction means that further work will be required to disentangle the causal mechanisms underlying these relationships.Lake populations of Daphnia varied substantially in investment in sex, with some populations reproducing entirely asexually throughout the study period and others shifting almost entirely to sexual reproduction by late autumn. We found that higher Daphnia density and parasitism were associated with greater investment in sex.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/168451/1/ece37847_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/168451/2/ece37847.pd

Hawaii versus Eastern Cross Infection

Data from laboratory infections with monarchs and parasites from the eastern North American and Hawaiian populations. Additional details can be found in the ReadMe file

Data showing effects of AMF on parasite virulence in the main experiment

Plant species: 1: A. curassavica; 2: A. verticillata; 3: A. purpurascens; 4: A. syriaca; 5: latifolia; 6. incarnata. AMF treatment: 0: control; 1: low; 2: high

Miami versus Eastern CrossInfection

Data from laboratory infections with monarchs and parasites from the eastern North American and Hawaiian populations. Additional details can be found in the ReadMe file