Phylogenetics of Dracunculus Nematodes in North America

Madeline Giner, from the University of Texas at San Antonio, studied the phylogenetics of Dracunculus in the lab of Dr. Christopher Cleveland.

The Dracunculus genus contains parasitic nematodes that infect a variety of hosts, including reptiles and mammals. Dracunculus medinensis, the Guinea worm, has gained much attention due to its history of infecting humans. Less studied are other dracunculids, including Dracunculus insignis and D. lutrae which are native to North America. D. insignis can infect a variety of mammalian hosts, whereas D. lutrae specifically infects North American river otters (Lontra canadensis). The goal of this project was to investigate the genetic diversity of Dracunculus in wildlife species from the Eastern USA and investigate spatial and host patterns of infection. Phylogenetic relationships were examined using the cytochrome c oxidase I (COI) gene targets. We hypothesized otters would predominantly have D. lutrae, and D. insignis would be identified from other hosts. Our experimental methods included DNA extraction, gene-specific amplification (PCR), Sanger sequencing, and phylogenetic analysis using the software Geneious. Our results indicate that a majority of worms from otters (19/65), raccoons (Procyon lotor, 22/22), and Virginia opossums (Didelphis virginiana, 2/2) were D. insignis. However, a worm from an otter from Florida had 100% identity to a novel Dracunculus sp. previously detected in Georgia, and a Georgia otter worm is closely related to another novel dracunculid species from Florida. In conclusion, D. insignis was present in most locations and hosts, D. lutrae is absent, and an additional host is now known for two novel Dracunculus species. These data provide new information about Dracunculus diversity in US wildlife, but additional investigation is required.


What’s The Buzz Around Hydrogen Peroxide? An analysis of honey bee preference and mortality to differing hydrogen peroxide concentrations

Carlos Martinez-Mejia from New York University worked with Dr. Lewis Bartlett.

Abstract Hydrogen peroxide has proven antimicrobial benefits and is created in honey when honeybees add glucose oxidase. This behavior makes honey bees another self-medicating animal and gives honey the longevity and antiseptic properties that we see. Hydrogen peroxide has been tested for toxicity in honeybees as well as parasites found in colonies. Honeybees have previously been seen to withstand higher concentrations of hydrogen peroxide than their insect counterparts. However, the exact toxicological limit of hydrogen peroxide that honeybees can withstand has not been officially established. Likewise, understanding if honeybees can identify these different concentrations and if this changes their preferences is still under investigation. Here we show that honeybees avoided hydrogen peroxide solutions in both sucrose and glucose when compared to the control sugar solution- differences in concentration and sugar were found to be significant in preference behavior. In addition, as hydrogen peroxide concentration increases- as does the proportional death of honey bees. At 4% H2O2 less than 40% of honey bees died. Knowing that hydrogen peroxide production for honey bees is a very metabolically taxing process- the hypothesis was that honey bees would rather have higher concentrations than go through the tiring process themselves. The results instead showed that on average honey bees avoided hydrogen peroxide when compared to the control sugar solution. Similarly, although honey bees have a higher tolerance toward hydrogen peroxide than other insects- 10% H2O2 was believed to be fully lethal but in some cases as many as 30% of honey bees survived at this dose. These results shed light on the relationship that honey bees have with hydrogen peroxide both regarding possible preference and toxicity threshold. We anticipate these trials to be a starting point for future pollinator health and pest control studies. Understanding the robustness of honey bees to such high concentrations of hydrogen peroxide opens the door for pesticide research that can effectively terminate pests while leaving the mass majority of honey bees unscathed.


Effects of parasites and predators on heart rates of Daphnia laevis using an innovative electronic stethoscope

Lutchie M. Carrasquillo, a student at the University of Puerto Rico at Arecibo, worked with Christian Hurd and Dr. Andy Davis to study the effects of parasitism on Daphnia heart rate using a new methodology.

Abstract: Daphnia are a model organism often used in investigations of chemical toxicity, and for biology classes. Measuring changes in heart rate is a commonly-used approach to assess responses to toxins. However, these assessments are usually done manually, which is time consuming and tedious. We developed a novel apparatus for monitoring changes in Daphia heart rates in real-time, without harming the animals. We used this approach to investigate how heart rate changes in response to naturally-occurring parasites (epibionts) and a natural Daphnia predator (glassworms). Our results showed Daphnia heart rates were not greatly affected by these, but we did discover an unusual diurnal effect, where the heart rate response differed between the morning trials and the evening trials.


Wolbachia and its effects on mating preference in two Drosophila species

Kareena Collins, a students at the University of Maryland Eastern Shore, worked with Paul Ginsberg and Dr. Kelly Dyer.

Abstract: Wolbachia is a maternally inherited intracellular endosymbiont that can manipulate reproduction in many different species of arthropod hosts, enabling its invasion into novel host populations. The most common types of reproductive manipulation is cytoplasmic incompatibility (CI), where mating between an uninfected females and infected males results in embryonic mortality.  Two Drosophila species, D. recens and D. subquinaria, were used to investigate whether Wolbachia can affect mating preference in a native versus non-native host species. D. recens is the infected species of Wolbachia with a frequency ~ 98%, while D. subquinaria is the uninfected host of Wolbachia. In the geographic region where both species overlap there is gene flow between species. We introgressed Wolbachia from D. recens into D. subquinaria in the laboratory. Both species show the CI phenotype in the lab when there is a cross with an uninfected female and an infected male. We conducted no choice mate trials for all crosses among infected and uninfected individuals for each species (all intraspecific crosses), and watched for mating for a three hour observation period. We found that Wolbachia had no effect on mating preference in the native host, D. recens. However, in the non-native host, D. subquinaria, Wolbachia had a huge effect on mating preference, with a significant reduction of mating rate in the cross between an uninfected female and an infected male ( the “incompatible” cross). Because Wolbachia had such a significant effect on mating preference only in the non-native host of D. subquinaria, it has potential implications for Wolbachia’s inability to become established as a native host in the population and/or species.


Reproduction and immunity trade-offs in Aedes aegypti mosquitoes

Jillian Dunbar, a student at the University of Alabama, worked with Ellen Martinson and Vincent Martinson in the lab of Dr. Michael Strand.

Reproduction and immunity are metabolically expensive systems; therefore, organisms with a limited amount of resources have to invest carefully (Schwenke et al. 2016). With the goal of producing offspring, organisms must invest resources into reproduction, yet also reserve resources for protecting themselves. In many cases reproduction and immunity are not directly linked. However, it has been shown in Aedes aegypti mosquitoes that, in addition to inducing egg production, a blood meal also increases the number of circulating immune cells called hemocytes (Castillo et all. 2011; Castillo et al. 2006). These findings elicit the question, does reproduction (blood-feeding) result in lower immunity for the mosquito? Through a variety of bacterial injections into blood-fed and non-blood-fed mosquitoes, this project worked to understand the possible tradeoffs between immunity and reproduction. We found an inverse relationship between immunity and reproduction, in that mosquitoes laid fewer and smaller eggs when injected with both live and heat-killed bacteria, but only for the more virulent species and higher doses. Interestingly, the results also showed that blood-fed mosquitoes were more successful in clearing or tolerating less virulent bacterial infections, suggesting resources gained from a blood meal are used to produce an anticipatory immune response. These preliminary findings are essential for continuing research and strengthening our understanding of the A. aegypti immune system with hopes of controlling or preventing diseases propagated by A. aegypti in the future.


Castillo, J, Brown, MR and Strand, MR (2011) Blood feeding and insulin-like peptide 3 stimulate proliferation of hemocytes in the mosquito Aedes aegypti. PLoS pathogens 7: e1002274.

Castillo, J, Robertson, A and Strand, M (2006) Characterization of hemocytes from the mosquitoes Anopheles gambiae and Aedes aegypti. Insect biochemistry and molecular biology 36: 891-903.

Schwenke, RA, Lazzaro, BP and Wolfner, MF (2016) Reproduction–immunity trade-offs in insects. Annual Review of Entomology 61: 239-256.


Virulence-related characteristics of Bordetella pertussis mutants deficient in intracellular survival

Callie Effler, a student at Lee University, worked in the lab of Dr. Eric Harvill.

Abstract: Intracellular survival is a common trait among human pathogenic bacteria that has advantages for the bacteria’s protection from the host immune response, persistence, and dissemination within the host. Bordetella pertussis, the gram-negative bacteria that causes whooping cough in humans, is commonly regarded as an extracellular pathogen. However, it has been recovered from macrophages in in vitro experiments, and reported anecdotally in clinical samples. It is unknown what contribution to pathogenicity the intracellular population has, if any, on the host. In this work, our broad objective was to evaluate the impact of B. pertussis’ intracellular survival and its role in pathogenicity. To do so, we planned to identify mutants similar to the wild type in general measured aspects of virulence, but that failed to survive inside of macrophages. A transposon library of B. pertussis UT25 was screened, resulting in the identification of several putative mutants that were deficient in intracellular survival. These strains were further screened for intracellular deficiency as a confirmatory measure, and went through further in vitro assays screening for cytotoxicity, hemolytic activity, resistance to serum complementation, and general fitness (growth). Based upon these assays, mutant strain G4 was the best candidate among those tested for an intracellularly-deficient mutant with similar virulence-related characteristics to the wild type. Preliminary C57 mouse infection studies suggest that the mutant strain behaves similarly to the wild type in vivo, indicating that intracellular survival may not be contributing to virulence. It is hypothesized that intracellular survival may be a phenotypic remnant of an ancestral strain of B. pertussis that transitioned from the environment to a become a human pathogen using this trait.


Effects of larval density on the fitness of the Asian tiger mosquito (Aedes albopictus)

Courtney Schreiner, a student at the University of Idaho, collaborated with fellow REU student Taryn Waite, along with Nicole Solano, Dr. Courtney Murdock, and Dr. Craig Osenberg.

Abstract: We were interested in studying the effects of larval density on the fitness of the Asian tiger mosquito (Aedes albopictus)­­. Aedes albopictus live all around Georgia and in various types of habitats that can support varying amounts of larvae. This creates competition which can effect downstream traits like fitness and disease transmission. Our experiment took place in a semi-field enclosure. We had 7 different larval density treatments that ranged from 5 to 240 larvae in each jar, for a total of 92 jars. Daily emergence, sex ratio and wing size were all recorded for all emerged mosquitoes. Overall we found that the proportion that survived, proportion female, fecundity, and wing size all decreased as density increased. We calculated the intrinsic growth rate using these estimates and found that lower densities have a higher intrinsic growth rate than those at lower densities. This told us that mosquitoes have a higher fitness at lower densities. Which also means that higher disease transmission would also be found in lower densities.


Spiders as a gauge for change: linking spider density to riparian habitat structure

Lily Tanner, a student at New College of Florida, worked with Denzell Cross and Dr. Krista Capps.

Abstract: Urbanization often compromises the diversity and abundance of native species living in watersheds (Rodrigues et al., 2015). Research has shown that riparian spiders are susceptible to land use change associated with urbanization (Sanchez-Ruiz et al., 2017).  We conducted  a spider density survey in riparian habitats in and around Atlanta as a metric to assess the impact of urbanization on regional spider populations. We hypothesized that if overhanging vegetation was important web-building substrate for some taxa  and vegetation provided cover for ground-dwelling species, then the highest density of spiders would be found in transects with vegetation hanging over the stream. Our results indicate that overhanging vegetation was related to higher densities of web-weaving species. Increasing amounts of overhanging vegetation was also related to increasing bank slope, suggesting there may be potentially important interactions between physical and biological characteristics of riparian areas that mediate spider population structure.


To skip or not to skip: exploring the connections between orviposition behavior and density –dependence in Aedes albopictus mosquitoes

Taryn Waite, a student at Colby College, collaborated with REU student Courtney Schreiner, Nicole Solano, Dr. Craig Osenberg, and Dr. Courtney Murdock.

Abstract: Conspecific density in larval habitats is an important factor affecting adult fitness in Aedes albopictus mosquitoes, as it drives competition for food and space. We conducted a larval density experiment wherein mason jars containing leaf infusion and varying numbers of larvae were placed in a field enclosure, developmental stage was recorded daily, and emerged adults were collected. Nonlinear regressions were performed on the data for survival to adulthood, sex ratio of adults, and wing length of females, and fecundity was inferred from wing length. Using these regressions, an equation was created to predict short-term population dynamics in habitats with varying conspecific densities. What determines the densities that will actually occur in various larval habitats is where females choose to lay their eggs. Female mosquitoes have the ability to skip-oviposit, which entails spreading their eggs out among multiple habitats instead of dumping them all in one habitat. The population dynamics equation was used to evaluate the theoretical consequences of skip- versus non-skip- oviposition, using scenarios with varying numbers of egg-laying females and a fixed number of available larval habitats. We found that at low densities of ovipositing females, skip-oviposition produces more short-term population growth than non-skip-oviposition. At higher densities, non-skipping becomes more productive than skipping, though there is less divergence between the outcomes. This simulation demonstrates a way in which patterns of density-dependence could act as a link between oviposition behavior and population dynamics. Due to the effects that we found of density dependence in larval habitats, individual females’ oviposition behavior could have consequences for short-term population dynamics.


Extreme heat reduces fitness of monarchs and their parasites

Maya Sarkar, a student at the University of Minnesota, worked with Isabella Ragonese, Dr. Sonia Altizer and Dr. Richard Hall.

Abstract: It is important to understand the consequences of a warming climate, especially in organisms that are more sensitive to temperature changes and where the outcome of warming may not be intuitive. This project used the Monarch-OE system to study how temperature may affect host-parasite interactions. The monarch butterfly (Danaus plexippus) is an iconic North American migratory species and the specialist protozoan parasite OE (Ophryocystis elektroscirrha) is present in all monarch populations. It has been shown that monarch development proceeds faster with increasing temperatures and that increased temperature exposure lowers OE spore infectivity over time. However, the effect of temperature on the host and parasite during active infection is not known. This project examined how temperature affects the monarch-OE system, focusing on the interaction between monarch immune function and parasite replication. Monarchs were inoculated with strains of OE parasite and placed in different temperature treatments. Three lineages (B,F, and D) of migratory monarch were used to test genetic effects, while 2 spore lines (E3 and E10) were used to study virulence effects within 5 different temperature treatments (18, 22, 26, 30, and 34°C). The results of this study provide novel insight to how extreme temperatures affect the fitness of a host and its parasite.


Copepod survival in water bowls exposed to typical Chadian ambient temperatures

Zavier Eure, a junior from North Carolina A&T, worked with the lab of Dr. Michael Yabsley to study copepod survival in different types of water bowls.

Abstract:  Guinea Worm Disease (GWD), caused by the nematode Dracunculus medinensis, has been detected with increasing incidence among dogs in Chad, Africa. Cyclopoid copepods (freshwater crustaceans) are intermediate hosts for D. medinensis. Currently the route(s) of D. medinensis transmission to dogs is still unknown but drinking from unprotected water sources would pose a risk. Dogs have access to water dishes provided for domestic animals and depending on the source of water, these dishes could harbor infected copepods, thereby acting as a source of transmission. To determine how long copepods survive in water dishes when exposed to Chadian ambient temperatures (41.1ᵒC), copepods were placed in three different container types (plastic, glass, and metal) and heated to 40ᵒC. Our results indicate that under simulated Chadian temperatures, metal dishes result in the highest rate of copepods death in the shortest period of time (2hrs) and were the only container to reach 100% copepod mortality. Conversely, plastic dishes exhibited the lowest mortality of copepods. These results indicate that the type of dish used when supplying water for animals in Chad is an important consideration in terms of preventing or interrupting transmission of D. medinensis among dogs.



Download (PDF, 1.38MB)

Using long-term science data to examine relationships of wastewater infrastructure and water quality

Sarah Williamson, a junior from Baylor University, worked with Denzell Cross in the lab of Dr. Krista Capps.  They used community-collected data to examine spatial and temporal changes in water quality in a local watershed.

Abstract:  The integrity of freshwater systems throughout the world is threatened by increasing concentrations of gut bacteria, such as E. coli. In urban watersheds, increases in bacterial concentrations are associated with intentional municipal wastewater discharge and aging and obsolete wastewater infrastructure (e.g., sewage leaks and failing septic systems). Tracing sources of bacterial contamination in surface waters is often difficult due to the need for long-term monitoring. Moreover, long-term monitoring can be time intensive and costly.
Community science organizations can be a cost-effective way to collect large amounts of environmental data across broad spatial and temporal scales. However, data collected by community scientists are often criticized due to concerns about scientific rigor, data fragmentation, and inaccuracy. Other work has demonstrated that groups employing robust protocols can produce data that align with data collected by professionals, and can be used reliably in decision-making processes pertaining to environmental health and watershed management. The purpose of this study was to examine spatial and temporal changes in water quality using data collected by community scientists of the Upper Oconee Watershed Network, and use community data to investigate relationships between water quality metrics and wastewater infrastructure in Athens-Clarke County (ACC). Specifically, we wanted to ask if water quality metrics (i.e., conductivity and turbidity) correlated to fecal bacteria concentrations in ACC surface waters and if there are relationships between site- and watershed-specific concentrations of E. coli and the proximity and density of wastewater infrastructure. We found that turbidity may be a strong predictor in bacteria concentrations however, the relationship between bacteria and conductivity was not clear. Our data also suggests that there may be important links between wastewater infrastructure and reduced water quality.

What’s the buzz? An investigation on how urbanization impacts mosquito species distribution

Lilith South, a junior from the University of Georgia, worked with Mike Newberry in the lab of Dr. Courtney Murdock to study the relationship between urbanization and distribution of mosquito species.

Abstract:   Impervious surfaces, mainly paved roads and buildings, significantly impact microclimate by making an area hotter and less humid. For this reason, urban areas are warmer than less developed rural areas. Heat associated with high impervious surface coverage impacts mosquito development and decreases larval survival in Aedes albopictus. Although many species of mosquitoes are present in Athens, Georgia, the most prominent species and most important species for human health, Ae. albopictus, is one of few species that dominate the area. Ae. albopictus has shown potential vectoral capacity for diseases such as Zika, Dengue, and Chikungunya. Fortunately, it does not yet transmit these diseases in the south eastern United States, but with changing climate and urbanization these diseases have potential to spread. The impact that impervious surface coverage has on mosquito community composition was not previously known. To investigate this effect, sites were classified and selected by their impervious surface coverage. Rural sites had impervious surface coverage ranging from 0-5%, suburban had 5-55%, and urban had 55-100% coverage.  Larval samples from each site were identified to species and the proportion of occupied habitats for each species in each site was noted. Overall, species richness decreased in suburban and urban areas with higher impervious surface coverage. Diversity was highest and there was a more even spread of species in rural areas. Contrary to what was expected, the percentage of Ae. albopictus occupied habitats did not significantly change with impervious surface coverage. Although previous studies suggest that Ae. albopictus is sensitive to hotter urban areas, this species may be more resilient than other mosquito species to the effects of urbanization. Knowing how urbanization impacts mosquito community composition can help researchers better understand disease transmittance and develop solutions for potential viral outbreaks.

Download (PDF, 1.07MB)

How does the proportion of sugar fed Aedes albopictus mosquitoes vary across land use?

Alyssa Slicko, a junior from the University of Arkansas Little Rock, worked with Nikki Solano in the lab of Dr. Courtney Murdock to look at sugar-feeding and its relationship to land use in an invasive mosquito.

Abstract:  The Asian tiger mosquito, Aedes albopictus, is a non-native species to North America and is known to be highly invasive with an ability to vector up to 27 different arboviruses. Since female mosquitoes feed on both sugar and blood to survive, understanding the tendencies for sugar feeding could explain the differences in the abundance of invasive mosquito populations. Past studies have shown that temperature plays an important role in the distribution of vector borne diseases, but it has not been discovered whether other environmental factors such as sugar availability is a limiting resource for mosquito populations. Some species have evolutionarily adapted to low sugar resources, meaning they primarily feed on blood. However, little is known about the sugar feeding habits of Aedes albopictus. We collected A. albopictus from nine field sites classified as suburban, urban and rural based on percentage of impervious surface. A backpack aspirator was used to collect mosquitoes that were then frozen and identified by sex and species. A total of 90 female A. albopictus mosquitoes were collected, 30 from each land use type. Using homogenized solution of each individual mosquito, colorimetric sugar assays were performed with serial dilutions to determine relative sugar content per mosquito. The absorbance values of these solution were read through a spectrophotometer. At the 1:4 dilution values, urban sites have the greatest overall amount of sugar followed by rural and suburban land uses. There is evidence that mosquitoes in Aedes albopictus females do sugar-feed and that there are differences between sugar contents across land use types. However, a negative relationship was found between absorbance and concentration values across sites. This could be due to a potential chemical inhibitor formed with highly concentrated mosquito dilutions not allowing complete reading of absorbance values and determination of sugar content.

Download (PDF, 876KB)

The world’s smallest escape artists: manipulation of the host innate immune response by Bordatella bronchiseptica

Margaret Dedloff, a junior at Clarkson University, worked with Dr. Monical Gestal in the lab of Dr. Eric Harvill to study the role of a sigma factor by bacteria in manipulating host immune response.

Abstract:  During the course of infection, some pathogens are able to sense and respond to the host immune system. This can cause prolonged pathogenesis, high transmission rates, and vaccine failure. One group of bacteria known to manipulate the immune response in varied ways is the Bordetella spp. B. pertussis, B. bronchiseptica and B. parapertussis are able to inhibit complement and suppress B and T-cell functions [1].  The BvgAS two-component system is understood to be a regulator of many virulence factors and is known as the master virulence regulon, however this is most likely an oversimplification. We hypothesized that pathogens like bordetellae should be under strong selective pressure to sense and respond to signals in blood and serum, in order to modulate immune defenses. When studying blood and serum responsive genes, we identified a putative sigma factor up-regulated in both conditions, and we hypothesized that this might be a regulator that dictates adaptation to pressure from the immune system. Here we identified the role of this sigma factor, the Bordetella Sigma Factor, or bsr, in manipulating the immune response. Through the use of a B. bronchiseptica bsr knockout and in vitro assays, we have found that bsr interferes with the innate response. bsr inhibits survival in macrophages by changing the dynamics of phagocytosis, causing macrophage death, and causing bacterial death and replication within the macrophage by interfering with cytokine and chemokine expression as well as differentially interacting with TLR receptors. This suggests that subsequent cell recruitment will be different within the host. Our results demonstrate that the bsr gene plays a critical role in Bordetella interaction with the innate immune system. A better understanding of this gene and its function will be valuable in efforts to create successful vaccines and treatments not only for Bordetella spp. but also for other bacterial species.

[1] Gestal M.C., Whitesides L.T., and Harvill E.T. “Integrated Signaling Pathways Mediate Bordetella Immunomodulation, Persistence & Transmission”. In revision, Current Trends in Microbiology.

Download (PDF, 1.88MB)

Identifying bacterial pathogens in natural Drosophila populations

Kailene Richbow Dozier, a junior at Virginia Union University, worked with Dr. Kelly Dyer to examine the pathogens present in wild populations of Drosophila.

Abstract: An estimated 70% of the world’s insects are infected with the gram-negative bacteria, Wolbachia pipientis. Wolbachia is known to protect organisms against viral pathogens, however little is known about how it interacts with bacterial pathogens. The aim of this study was to isolate and identify bacterial pathogens within wild, mushroom feeding Drosophila. With this knowledge, we hope that we can aid future research studies trying to understand how Wolbachia increases host resistance to bacterial pathogens as compared to viral pathogens. Two species of flies, Drosophila Putrida and Drosophila Tripunctata were captured from Oconee State Park located in Athens, GA. The captured flies were separated by gender. Female flies were put aside to generate Iso-Female lines, while male flies were homogenized and streaked onto LB agar plates for bacteria growth. Once colonies began to grow after incubation, they were isolated and morphologically identified. 35 bacterial isolates were obtained from the 18 D. Tripunctata flies streaked. 20 bacterial isolates were obtained from the 20 D. Putrida flies streaked. A total of nine bacterial species were identified morphologically, seven of which were shared between the two species of wild flies. Similarities between the abundance of Micrococcus luteus and Enterococcus within both species of flies were observed. D. Tripunctata was seen to slightly differ from D. Putrida by carrying the bacterium Bacillus subtilis and Bacillus megaterium. For future exploration, 16S gene sequencing is needed to accurately confirm the identification of the bacterial pathogens discovered. Afterwards, testing for pathogenicity of the bacterial pathogens needs to be conducted as well as testing for Wolbachia’s interaction with the pathogens.

Download (PDF, 1.02MB)

Influence of mosquito gut microbiota on susceptibility to dengue infection

Robert Manuel, a junior from California State Polytechnic University, Pomona, worked with Ruby Harrison in the lab of Dr. Mike Strand to examine the relationship between mosquito gut biota and dengue infection.

Abstract: The mosquito Aedes aegypti is the primary vector of dengue virus (DENV). Prior studies report increased susceptibility of A. aegypti to DENV infection, and higher pathogen burden when adult females are treated with antibiotics. This suggests a role for the microorganisms that colonize the digestive tract of mosquitoes (gut microbiota) in susceptibility to DENV infection. We tested the hypothesis that microbe-depleted A. aegypti are more susceptible to DENV infection by comparing three treatments: axenic mosquitoes with no gut microbiota, gnotobiotic mosquitoes harboring only Escherichia coli, and conventional mosquitoes with a natural community of gut microbes. We validated the status of these mosquitoes using both culturing methods and PCR. We then assessed DENV presence/absence in each treatment fourteen days after feeding adult females an infected blood meal. Consistent with our working hypothesis, a larger proportion of axenic mosquitoes were infected with DENV than conventional mosquitoes. Proportions of axenic and gnotobiotic mosquitoes infected with DENV were nearly identical. However, our treatments had no effect on DENV dissemination among females that were infected. In summary, these results suggest A. aegypti with a more diverse gut microbiota are more resistant to DENV infection than axenic females but E. coli alone provides no increase in resilience.

Download (PDF, 709KB)

Behavioral and environmental determinants of parasite transmission in a butterfly host

Chastity Ward, a senior from Fayetteville State University, worked on a project with Dr. Sonia Altizer, Dr. Richard Hall and Dr. Paola Barriga to examine how parasites of the Monarch butterfly are transmitted.

Abstract:  Many pathogens can be transmitted when infectious stages shed into the environment are later encountered by susceptible hosts. Environmental transmission is common among insect parasites, and also occurs for human diseases such as cholera and polio. Understanding how host behavior and environmental variables affect the shedding of infectious stages is crucial for predicting patterns of infection risk. Monarch butterflies Danaus plexippus are commonly infected by the protozoan Ophryocystis elektroscirrha (OE); this parasite is transmitted environmentally when infected adults deposit spores onto host plants (milkweed) that are consumed by monarch larvae. To quantify host contact with milkweeds as an estimate of parasite transmission, we set up outdoor flight cages with adult monarchs and milkweed plants. Cages varied in the number of adult monarchs and milkweed plants, and were assigned to one of two milkweed species. We used captive-raised monarchs from several genetic lineages, and marked the monarchs with unique number and color codes to track activity. We observed cages for replicate intervals over a week-long period, during which we noted observed monarch contacts with plants, and recorded monarch and plant identity, activity type, temperature, weather, and time of day. Our results showed strong heterogeneity in plant visitation rates among monarchs that was best explained by monarch sex (females had 4.7 times higher visitation rates than males, owing to frequent oviposition on milkweeds).  We also found wide variation among individual plants in the number of visits by monarchs. Milkweed species, plant flowering status and plant leaf number did not affect visitation rates, but plants in cages with a higher number of monarchs were visited more frequently. In sum, our findings provided evidence for individual monarch’s serving as superspreaders of infection, and for some milkweed plants serving as hotspots of infection. This study provides a starting point for estimating environmental parasite transmission in wild milkweed patches, and suggests that individual-level heterogeneity might be more important than environmental variation in driving parasite transmission in this system.


Download (PDF, 4.56MB)

Nematode parasite reduces the fight or flight reaction in its host

Felicia Ebot-Ojong, a junior from the University of Georgia, worked with Dr. Andy Davis to study the effect of nematode parasites on the fight-or-flight reaction of infected beetles.

Abstract:  Parasites cause a range of unfavorable effects on host fitness, including reducing available energy. This could be detrimental in situations where the host needs to escape a harmful situation (in a “fight-or-flight” situation), though this is rarely studied in parasitology research. The bess beetle (Odontotaenius disjunctus) inhabits forests in the eastern United States and is host to a naturally-occurring nematode parasite (Chondronema passali), which can be extremely abundant within hosts. The goal of this project was to evaluate the how nematode infection affects the fight-or-flight responses of the beetles under simulated predator attack. A total of 150 beetles were collected locally and stored individually in plastic containers for 3 weeks. Each week, we assessed and video-recorded behavioral reactions to a series of “pokes and prods”, then scored level of the reactions in the videos. We assessed the number of vocalizations during attack, plus levels of physical resistance using a scoring system (Fig. 2). Beetles were later dissected and their level of nematode infection and gender was recorded. We found that beetles with nematode infections tended to have reduced fight-or-flight reactions to the predator attack compared to unparasitized individuals. The level of nematode infection had no effect on the amount of vocalization made by each individual during an attack. These results show that nematode infection has an energetic cost during situations where the host needs to respond quickly.

Download (PDF, 644KB)