2017 REU Projects

Blair, Craig (Oberlin College), Mentor: Courtney Thomason (Virginia Tech).
Testing the dilution effect: Exploring correlations between species richness and parasite infection in a small mammal community
Abstract:  The precipitous decline of global biodiversity, coupled with an increase in infectious disease spread, has led disease ecologists to propose hypotheses that explain the ecological factors influencing disease transmission. One of the best-known of these hypotheses is the Dilution Effect, which suggests that biodiversity protects against disease by diverting parasites from competent to incompetent reservoir hosts. Though widespread and well-known, the validity of the Dilution Effect is highly debated, and critics often argue that it fails to consider additional ecological factors that may influence disease transmission. With its long history of disease studies in Peromyscus mice, Mountain Lake Biological Station (MLBS) is an ideal system to study the effects of host species richness on the parasite loads of mice and other small mammals. Over the course of 10 weeks, I analyzed the fecal samples of small mammals at sites across MLBS and tested for correlations between biodiversity and infection levels. Additionally, I explored the effects of anthelmintic medication of mice on the infection levels of other mammals, and I measured habitat characteristics to look for covariates with overall infection prevalence. These data revealed a significant negative correlation between species richness and infection intensity of mice, indicating that more specious sites had lower infection levels. Furthermore, anthelmintic treatment of mice decreased the infection intensity of other mammals, indicating that mice are an important contributor to the host community’s parasite pool. Finally,  habitat data (driven mostly by percent of rock and log cover) is strongly correlated with overall infection prevalence, suggesting the possible influence of habitat characteristics on disease transmission. These results demonstrate broad support for the Dilution Effect, and provide an impetus for further examination of this hypothesis to better understand the relationship between habitat conservation and disease risk in natural systems.

Lawhorn, Kane (University of Tennessee), Mentors: Robin Costello and Butch Brodie (University of Virginia).
Analyzing the effects of mating behaviors on female dispersal in the forked fungus beetle, Bolitotherus cornutus
Abstract:  Dispersal is a fundamental process throughout ecology that entails an individual leaving one range and establishing in another. It is essential for the flow of genetic material and the reduction of intraspecific competition, and it can be motivated for environmental and social factors. Various studies, ranging across different systems, mention habitat suitability, social interactions, mating interactions, and behavioral factors that all influence dispersal. Although dispersal has been observed in the forked fungus beetle, Bolitotherus cornutus, the driving forces of dispersal are not understood. This study aims to determine the underlying factors that drive female dispersal in particular. We performed a mark/recapture study of forked fungus beetles at peripheral populations within a 60-meter radius of nine focal populations at Pond Drain at Mountain Lake Biological Station in Giles County, VA. By combining behavioral data collected in 2016 with movement data from 2017, we were able to determine if the frequency of mating behaviors, including mate guarding and courting, influences female dispersal. In addition, population characteristics and morphology were analyzed to see if they influence female dispersal. Using multivariate logistic regressions, we determined that mating behaviors do not influence female dispersal. Similarly, population characteristics and morphology did not have a significant effect on female dispersal between populations These results indicate the male mating behaviors do not influence female dispersal. Further research is needed to accurately determine the drivers of female dispersal between populations.

Collazo Perez, Stephanie (University of Puerto Rico - Río Piedras), Mentor: Adriana Herrera Montes (University of Puerto Rico - Río Piedras).
Relationship between disturbances and morphological traits in salamanders
Abstract:  Disturbance is any event that causes a disruption to the current event of an ecosystem (Pickett 1988). Perturbations in the landscape, whether natural or anthropogenic, can alter the ecosystem causing stress affecting the populations by eliminating foraging and breeding sites, disrupting the connectivity of habitats, and affecting the dispersal and modifying microhabitats (Delgado-Acevedo & Restrepo 2008). This stress can also affect the individual altering their morphological traits and at the same time the fitness or performance and the ability to inhabit disturbed areas. Based on previous studies of changes in morphological traits in amphibians when compared to different habitats and disturbances (Maerz et al. 2006, Delgado-Acevedo 2008) and the history of perturbance in the region of Mountain Lake in Giles County, Virginia, I want to determine the relationship between disturbances and morphological traits using the salamanders as my model organism; this group has been subjected to disturbances which have already affected its abundance (Petranka et al. 1992, Marsh & Beckman 2004). For this study, I measured and compared the total length and body mass of 150 individuals from five different disturbed areas using the Scaled Mass Index (SMI). Data suggests changes in body mass and length associated to different disturbances.   This variations in morphology between disturbances can help us understand the impact anthropogenic disturbances have on the ecosystem and the effects it may have on the species.

Finn, Sylvana (Skidmore College), Mentors: Robin Costello and Butch Brodie (University of Virginia).
The effects of social network position on dispersal in the forked fungus beetle (Bolitotherus cornutus)
Abstract:  Dispersal from one habitat to another is a fundamental ecological process that occurs throughout all taxa. An individual’s social environment may be one of many factors that determines if and when an individual disperses. Social network analysis is one way to holistically quantify a social environment an individual experiences. Although social environment has been studied extensively in relation to dispersal, there has been little research on how an individual’s position in a social network may influence dispersal. Social network position can have varying fitness consequences at varying sized populations. This study examines the effect of social network position on dispersal from populations of varying sizes in the forked fungus beetle, Bolitotherus cornutus. The study was conducted at Mountain Lake Biological Station, by surveying 121 populations for marked individuals from last year’s breeding season. We used multivariate logistic regressions to analyze movement probabilities in response to social network metrics and population size. We discovered that the social network metric, betweenness, predicts movement, such that in small populations, individuals with greater betweenness are less likely to disperse, whereas in large populations, betweenness does not predict movement. These results illustrate that social network position may be one aspect of the social environment that influences dispersal, and furthermore, that this dispersal may be in response to some fitness consequence associated with the network metric. Furthermore, the movement of individuals with small betweenness in small populations corresponds to a movement away from small populations where an individual might possess lower fitness as a consequence of low betweenness.

Martin, Bruce (Skidmore College), Mentor: Chloe Lash (University of Tennessee).
Strength in numbers? Examining the effect of colony size on social immune systems in Aphaenogaster ants
Abstract:  Many studies assume that eusocial insects are particularly vulnerable to disease because they live in large, dense groups, which may facilitate the rapid spread of pathogens between infected and susceptible individuals. However, empirical research has failed to confirm such a pattern, often showing that higher group sizes instead confers immunological advantages due to the highly evolved social immune systems of eusocial insects. These insects seem to prevent epidemics in part through contact-based, social transfer of immunity (i.e. immune priming), increasing overall colony immunocompetence. However, the effect of group size on immunocompetence in eusocial insects at large, colony-level scales, and the relationship between group size and immune priming remain relatively unexplored. In this study, I characterize the effects of group size and immune priming on survivorship in Aphaenogaster colonies exposed to the generalist entomopathogenic fungus Beauvaria bassiana. Relative risks of death for adult workers were analyzed using a Cox proportional hazard regression. I provide strong evidence that priming Aphaenogaster ants with a sublethal dose of B. bassiana elicits a positive effect on survivorship. I also show that colony size interacts with priming treatment and pathogen exposure in complex ways, extending and qualifying the results of previous experiments. This adds to a growing body of evidence that immune priming is a widespread and significant phenomenon in invertebrates, and demonstrates that small-scale trends in the social immune function of ants cannot be reliably extrapolated to larger scales. These results have implications for both managing pest eusocial insects and the field of wildlife epidemiology in general.

Orengo Rolon, Juan Luis (University of Puerto Rico - Río Piedras), Mentor: Adriana Herrera Montes (University of Puerto Rico - Río Piedras).
Ecosystem services provided by woody vegetation and salamanders in disturbed areas
Abstract:  The main objective of this study was to evaluate if there is a relationship between ecosystem service provision and different types of disturbances. I worked in the Appalachian forest region, specifically Mountain Lake Biological Station (MLBS) and surrounding areas. The disturbances under study will be: forest fires, presence of deer, construction of housing and roads, and an old growth forest as a control area. In order to study alterations to service provision on behalf of the ecosystem, two model taxonomic groups were selected, woody vegetation and terrestrial salamanders. The woody vegetation service that we focused on was habitat provision for terrestrial salamanders. To evaluate services provided by salamanders, I estimated the relative abundance of salamanders after cover object surveys were performed in each study site. At the end of the study I found that the most permanent disturbances (road and housing) differed from the least permanent one (deer and fire) in the habitats structure. We also found that the minimally disturbed control sites contained more sensitive species (Plethodon glutinosus) when compared to the disturbed sites.

Sturiale, Samantha (University of Virginia), Mentor: Chloe Lash (University of Tennessee).
Elaiosome collection as a potential mechanism of self-medication in Aphaenogaster ants
Abstract:
  Some animals supplement their own immune system with ingestion (pharmacophagy) or topical application (pharmacophory) of secondary plant metabolites, a behavior known as self-medication. This response can be classified as prophylactic if it is exhibited preventatively in both presence and absence of the pathogen or as therapeutic if practiced exclusively during pathogen challenges. Much self-medication literature has focused on mammals, but this behavior is also found in caterpillars and even eusocial insects, such as bees and wood ants. For example, wood ants practice prophylactic resin collection and therapeutic collection of hydrogen peroxide. However, the extent of therapeutic self-medication behaviors in ants using natural diet options remains under-studied. Additionally, few have explored pharmacophagy, rather than pharmacophory, in any eusocial insects. Using standard cafeteria preference experiments with insect corpses and S. canadensis diaspores, I show that Aphaenogaster ant colonies, when challenged with an entomopathogen, therapeutically self-medicate by preferentially increasing collection of elaiosomes with antimicrobial chemicals. Furthermore, I show that the presence of brood increases collection of elaiosomes, further supporting the idea that elaiosomes are preferentially fed to brood and supporting the idea of self-medication, as brood are more susceptible to infection. Finally, I study the effects of metapleural gland blockage on foraging preferences. Results showed no evidence that metapleural gland blockage, within its interaction with pathogen presence, increased diaspore collection as was hypothesized.

Tompros, Adrianna (Colorado State University), Mentor: Courtney Thomason (Virginia Tech).
Parasite co-infection and immune response: Composition of the parasite community and its effect on leukocyte profiles
Abstract:  Hosts are rarely infected with only one parasite; rather hosts usually harbor multiple parasites, forming a complex community. Parasites have developed and utilize different, refined mechanisms to adjust the immune response, allowing them to persist and reproduce in their hosts. These mechanisms include immunosuppression, temporary or permanent dysfunction of the immune system, and immunoevasion, counteracting the immune response to a specific pathogen. Due to co-infection, immunosuppression and immunoevasion mechanisms and interactions between parasites and the host are occurring simultaneously, which can have immense effects on the host immune response. The aim of this study was to determine how different intensities of parasites may affect host immune response, which was represented by leukocyte profiles. Then, a “key” parasite, nematodes, was removed from the host to determine its effects on the host immune response. Peromyscus mice were trapped and fecal and blood samples were taken and used to quantify parasites (e.g. infection intensity) and leukocytes (e.g. host immune response). We found that coccidia infection had no significant effect on leukocytes while nematode infection did have a significant effect, expectedly increasing both eosinophils and leukocytes. Co-infection of nematodes and coccidia had lower eosinophil proportions than solely nematode infection and as coccidia burden increased in co-infected individuals, neutrophils decreased and eosinophils increased.  By investigating the effects of parasite intensities on leukocyte profiles, further insight into parasite co-infection and how it corresponds to immune response may be achieved. Understanding which combinations of parasites and what intensities are correlated with specific immune responses, more specifically Th1 versus Th2, is extremely critical in understanding how parasites play a role in disease dynamics, disease outbreak, disease treatments, vaccinations, and animal and human health.