Nectar, parasitism and flight in butterflies

When animals have unlimited access to food, they can often tolerate parasite infection and maintain high levels of growth and reproduction – but under food shortages, infected animals suffer more severe harm from parasites. This study examines the interactive consequences of food resources and parasitism for flight in a migratory insect, the monarch butterfly.  Migratory animals face extreme energetic demands during long migratory journeys, and some studies show that infected animals are less likely to survive long-distance migrations, in part owing to lower energy reserves of infected animals.  Monarchs are famous for undergoing a long-distance two-way bird like migration from breeding grounds as far north as Canada to wintering sites in southern Mexico.  Monarchs fuel their migration by accumulating lipid reserves from nectar resources during the fall. Monarchs are infected by a debilitating protozoan that replicates internally in caterpillars and pupae, and forms dormant spores on the outside of adults’ bodies. These parasites can lower monarch survival and reproduction, and past work showed that infected monarchs migrate less well than healthy butterflies. The proposed project test the flight performance of experimentally infected and healthy monarchs, fed different nectar diets. This study will examine the hypothesis that the flight performance of infected monarchs will suffer more under caloric restriction than the flight performance of healthy butterflies.

Mentors: Ashlew Ballew, Paola Barriga, Sonia Altizer
Type of project: Empirical, lab-based

Parasitism and Stress

Research in the Davis lab is broadly focused on animal “ecophysiology”, with study subjects ranging from birds, to butterflies, to beetles. REU students can make many contributions to these ongoing projects, with a combination of field work and laboratory experiments.  A recent thematic area involves asking, how can animals cope with the daily stressors in their lives while being parasitized? A useful study subject for these experiments is a common forest-dwelling beetle (horned passalus, pictured), which is naturally-parasitized by a seemingly benign nematode (pictured). This parasite appears to cause little outward harm to its host, but during times of duress or heightened activity, there is in fact an observable cost to being parasitized.

In the summer of 2020, an REU student will conduct an experiment that tests the behavioral and physiological reactions of parasitized and unparasitized beetles to a mild, non-lethal stressor, to further understand how parasites impact their hosts. The details of this project will depend in part on the interests of the student. The ideal applicant for these projects is someone who is OK with traipsing through chigger-infested forests, is able to work with (handle) bugs, and who is not squeamish about icky dissections.

Mentor: Andy Davis
Type of project: Empirical, Lab- or field-based

Understanding hydrogen peroxide employment by honeybees as an anti-parasitic social immunity tool

Hydrogen peroxide has immunological function across a broad suite of life on earth, and is still used in the US as a common antiseptic. Honeybees are another self-medicating social animal also known to use hydrogen peroxide manipulation – mostly in honey production; this in part makes it the only naturally occurring foodstuff to never spoil and underpins part of its medical applications in wound healing. Previous undergraduate work with UGA and Emory University investigated whether hydrogen peroxide content in honey poses a toxicity risk to a macroparasite, the small hive beetle, in addition to its antimicrobial effects. Dr Lewis Bartlett is currently trialling novel small hive beetle control methods, and this project will integrate with that work to further establish: ranges of hydrogen peroxide content in naturally occurring honey across different nectar sources, honeybee tolerance of hydrogen peroxide consumption and whether it exceeds that of other insects, and toxicity of hydrogen peroxide to juvenile and adult small hive beetles with the potential for it to be employed as a parasite control agent. The study will further be framed in the context of floral diversity and pollinator health, by determining whether different plants favour the production of honey with different antiparasitic or antiseptic properties through. The student will undertake empirical entomological toxicity trials and basic entomological rearing at the UGA honey bee lab, as well as data analysis and visualisation focussed on assessing survivorship, with the aim to produce a concise scientific publication; they will also have the opportunity to learn field skills in apicultural research if they wish. The student will also be given the option to attend (for free – including transport from Athens, meals and accommodation) a leading honeybee conference in North Georgia ( as an introduction to the system in the week of May 11th – 16th, prior to the official REU start date of May 18th.

Mentor: Lewis Bartlett
Project Type: Empirical, lab- and field-based

Specific Requirements: Student cannot have a known allergy to honeybees, and must have no objection to euthanasia or experimental destruction of live insects for research purposes.

Honeybees in a hive

How parasites influence ecosystems: studying the varied effects of a trematode parasite on its environment

Historically, parasites have been primarily studied for their negative effects on human and animal health. However, the scientific community is becoming increasingly aware that parasites can have complex effects on their ecological communities (Dunn et al. 2012, Mischler et al. 2016), and in some cases can benefit the ecosystem (Davis and Prouty 2019). How parasites alter ecosystem processes and nutrient cycling remains relatively unexplored, despite calls to address this question (Raffel et al. 2008, Hatcher et al. 2012). However, this question is vital because such research could provide novel insights into both human and ecosystem health.  In addition to the direct impacts of parasites on host mortality and population growth, parasites can indirectly impact their communities and environments in subtle, but equally important ways (Buck and Ripple 2017). For example, parasites can alter ecosystem processes through changes in host physiology (Bernot and Lamberti 2008), nutrient excretion stoichiometry (Bernot 2013) and behavior (Lafferty and Ecology 1996) that have population and community-wide effects. For this project, we will investigate how a trematode parasite influences its snail host, Helisoma trivolvis, in terms of various host changes such as nutrient excretion, metabolism, respiration, foraging and behavior. The REU student will investigate these effects by comparing infected and uninfected snails in the lab. The majority of the work will be done in the lab, but there is possibility for field work and field manipulations given time and interest.

Mentors: Emlyn Resetarits and Jeb Byers
Type of project: Empirical, lab-based

Population Genetics of the Lyme Disease vector, Ixodes scapularis

The tick species Ixodes scapularis (Acari: Ixodidae) is the main vector in the United States for Borrelia burgdorferi, the causative agent of Lyme Disease. Previous research has identified behavioral differences between northern and southern populations of I. scapularis with northern nymphs spending more time above leaf litter increasing the likelihood for human contact. This difference in behavior is observed despite the environment, suggesting an unknown genetic driver to these behavioral patterns. This study will expand on a pilot study using ticks from Connecticut, South Carolina, and Minnesota that identified 99,187 SNPs distributed across 14,168 polymorphic loci using triple-enzyme restriction-site-associated DNA sequences (3RAD). This illustrates that I. scapularis populations have large amounts of intra- and inter-population variation. In this upcoming study we plan to assess 27 populations across the range of I. scapularis to elucidate the genotypes driving behavioral differences and Borrelia transmission. We are also interested in microbiome disparities across this range as it could have an impact onBorrelia transmission. The student will be trained and involved across the pipeline of this study: tick ID, DNA extraction, 3RAD and 16S library prep, and bioinformatics analysis.

Project mentors: Julia Frederick and Travis Glenn
Type of project: Combination of Empirical (lab-based) and Quantitative (computer-based)

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.