9) Evaluating the transmission mode of a nematode parasite within horned passalus beetles, Odontotaenius disjunctus

Horned passalus beetles live in decaying logs, where they excavate cavities for rearing young. They are commonly parasitized by a nematode, Chondronema passali

Mentor: Dr. Andy Davis
Abstract: Horned passalus beetles are a common forest insect in the eastern United States, and are host to a variety of naturally-occurring parasites, including a nematode that lives in the abdomen (Chondronema passali). Beetles can be heavily parasitized, sometimes with thousands of these worms, though there are many questions about how these nematodes transmit to other beetles. Ongoing work in the Davis lab has sought to determine the impact of these parasites to the host physiology and behavior. Recent projects have revealed how female beetles can be affected more so than males, including influencing their willingness to explore. This implies that the nematode could be causing a behavioral change to its host, to promote its own transmission during oviposition activities. This will be the focal question that will be explored in summer 2023.
A student will be tasked with conducting one or more lab-based experiments designed to help elucidate this question. This will include collecting beetles from local forests, housing them in the lab, overseeing behavioral experiments, and performing dissections to determine parasite loads. The details of the projects will be fleshed out when the program starts.
The ideal student for this project is someone who is interested in insects, animal behavior, parasites, and who is completely fine with looking for icky, squiggly worms in soil samples or within beetle carcasses.
Is the project computational, empirical, or both? Empirical.

Sensing Your Friends Getting Eaten is Stressful, Having a Parasite Makes it Worse

Helen Gloege, a student in Mount Holyoke College, worked in the lab of Dr. Andy Davis

Abstract Daphnia and other animals face a multitude of different stressors in their daily lives. Parasites can cause various physiological changes in animals, yet few prior studies have looked at the combination of parasitism and stress in animal models. This study used Daphnia which are microscopic plankton that may have ectoparasite-like organisms attached to their surface. Vorticella, a single-celled ectoparasite, is one of these organisms that can be found attached to Daphnia. During this experiment, when Daphnia ambigua were exposed to a “stressor” the vorticella parasite led to an increased heart rate in the Daphnia. The “stressor” was made of macerated Daphnia and aimed to simulate a predation event. Daphnia without vorticella present appeared to have no discernable reaction to the stressor. While Daphnia with vorticella increase the heart rate and physiological stress reaction in Daphnia. When over twenty vorticella were present on the daphnia the heart rate continued to increase during the study period.


Scared stiff: Effects of a nematode parasite on fearfulness in bess beetles

Anna Shattuck, a student from Tulane University, worked in the lab of Dr. Andy Davis.

Abstract Freezing is a defensive behavior seen in many different animals as a response to extreme threats such as predators. While research on freezing behavior is widespread, there is little known about how parasites may influence it. A non-lethal nematode parasite, Chondronema passali, can be found in the hemocoel cavity of bess beetles, Odontotaenius disjunctus. A single beetle can carry the burden of hundreds of these nematodes. Previous research has shown that parasitized beetles eat more and are more active, suggesting they are bolder and may be less prone to freezing. This experiment tests whether the nematode parasite influences fearfulness in beetles by exposing a population of bess beetles to different stressors and observing their freezing behavior in response to each. Following the trial period, beetles were dissected, and parasite load and sex were assessed. Out of 161 beetles, 14% were unparasitized by C. passali. We found that heavier parasite loads increase freezing durations in males and decrease freezing durations in females in response to a stressor. We suspected that female beetles experienced greater energy loss from being parasitized and laying eggs, making them more inclined to move and forage. To test this idea, we deprived 22 beetles of food for 48 hours in hopes they would display freezing behavior less when responding to a stressor. After being starved, only 4 beetles displayed freezing behavior, indicating fearfulness is tied to hunger.  Further investigation is needed in order to elucidate this relationship.


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.


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.

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A protozoan parasite weakens the stress reaction of monarch butterflies

Jovani Raya, a student from Abaraham Baldwin Agricultural College, worked with Dr. Sonia Altizer and Dr. Andy Davis to study the effect of infection on the stress reaction of monarch butterflies.

Abstract:  The protozoan parasite Ophryocystis elektroscirrha (OE) affects the adult mortality, longevity, body size, and flight ability of monarch butterflies (Danaus plexippus). However, very little research on how the parasite influences the stress response in monarchs has been conducted. We examined the effects of parasite infection and larval rearing densities on the monarch stress response. Monarch larvae were inoculated with parasite spores and reared in low (2 larva) or high (10 larva) densities. When the monarch larvae reached pupation, we assessed their stress reactions. To produce the stress response in the pupae, physical disturbance was applied for 20 seconds. After the disturbance, the pupa was placed on a device that detects movement within animal tissue and can record the movements of the heartbeat. This recording allowed us to count the number of beats per minute. The result showed that infection was a significant predictor of the magnitude and duration of pupa HR; infected monarchs had lower reactions. Lower reactions would negatively affect how well infected monarchs could cope with daily stressors, especially during the arduous fall migration.

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Can Internal Parasites Affect Wound-healing Rates in Insects?

Lexi Calderon, a student from the University of Redlands, worked with Dr. Andy Davis and members of his lab to study parasites affect wound-healing in bess beetles.

Abstract: By definition, parasites depend on the resources of their host to survive. This relationship can result in a decrease of energy and fitness for the host. The parasitic nematode Chondronema passali resides in the hemocoel cavity of the bess beetle, Odontotaenius disjunctus. Although this parasite is non-lethal, a single beetle can harbor thousands of nematodes. Previous research has demonstrated this parasite affects the stress reaction of beetles, but very little research has investigated the effect parasites have on the host’s ability to heal a wound. Wound healing can be thought of as an indicator of the effectiveness of the immune system and by studying healing we can infer the effect this parasite has on the fitness of its host. We conducted a series of experiments where beetles were wounded with a dremel rotary drill and observed every hour for 12 hours after initial wounding. Each hour beetles were given a value from 1-5 to measure their status in the wound healing process, and values were summed to generate a ‘wound healing score’ for each beetle. Beetles were killed and dissected following the experiment to define gender and parasite abundance. Out of 188 beetles, 83% were infected with C.passali. Wound healing scores were not significantly predicted by parasite status. Beetle weight was a predictor of wound healing scores where heavier beetles had higher scores. Oxygen consumption was also measured in a subset of beetles after wounding, and we found parasitized beetles tended to have higher respiration (10% higher) than non-infected beetles.

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Do Parasite Infections Effect Fighting Ability in Beetles

David Vasquez, a student from Virginia Tech, worked with Andy Davis in the Odum School of Ecology to examine the effect that parasite infections have on the fighting ability of beetles.

David Vasquez1, Andy Davis2

1Virginia Polytechnic Institute and State University,

2Odum School of Ecology, University of Georgia

Parasites, by definition, subsist off their host’s resources, which can drain energy. This can have negative consequences for the host, especially during energy-intensive activities. Fighting is common in most animals that are territorial, or that are protective of young. Few studies have examined the effect of parasites on fighting capacity in animals. The bess beetle (Odontotaenius disjunctus) is a saprolytic insect common in forests within the eastern United States, and it is susceptible to a naturally-occurring nematode parasite (Chondronema passali). We examined the effect of infections on the outcome of staged fights in this beetle. Beetles were selected based on weight (so that each pair contained similarly-sized individuals), then placed in a small wooded arena to observe fighting behavior. A video camera recorded 3 minutes of fighting. Afterwards, beetles were killed and dissected to determine gender and parasite status. From the videos, an external observer recorded the number of bouts, wins and losses for each pair, and the overall winner. A total of 78 beetles were used in the experiment; 40% were infected with C. passali. 31 infected beetles were the overall winner in 52% of their matches, while uninfected beetles won 48% of fights (this was not significantly different X2 test). However, when fights were grouped by infection severity, we found that beetles with the highest infection score (thousands of nematodes) won 71% of their battles, while the least-infected beetles only won 25% of the time. This is counter-intuitive to the idea that infection has a negative energetic effect on host fitness.

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